Synapsida

Why Forest Fires Are Good For You (if you're a big brown bat)

2012-02-26T13:27:00.000Z

Big brown bats

Forest fires are both destructive and spectacular. Not quite up there with volcanoes or tsunamis, perhaps, but nonetheless pretty dramatic, wreaking havoc on the local environment. Human-caused fires, when they get out of control, can be very damaging to the ecosystem, which may take years to recover. Yet forest fires have been around since long before humans, and, for at least some forests, they are just a natural part of the cycle of life. Indeed, there are some plants whose seeds germinate specifically after a local wildfire. But how does this affect animal communities?

One such environment is that of sandhill forests. Sandhills are so named because of their sandy, well-drained soils, often dominated by ash, but (unlike the much more barren sand dunes) they support significant plant communities. In the southeast USA, between Virginia and eastern Texas, the dominant tree in these forests is the longleaf pine. Frequent fires are essential for this species to do well, and, left without fire for too long, the nature of the forests change dramatically, in this case being replaced by denser oak woodland.

That's because, while acorns have no trouble germinating after a fire, the resulting saplings are easily destroyed when the next fire comes along - so if fires are too frequent, they just never get a chance to grow to their full size. Longleaf pine, on the other hand, has no such problem, because their saplings more closely resemble a tussock of spiky grass, with a bush of tightly packed needles sprouting from a very short trunk (it eventually shoots up rapidly to its full height, but this may be several years after it first sprouts). When a fire comes along, it singes the needles, but can't penetrate the dense spiky foliage to get at the heart of the plant, allowing it to survive while the oak trees around it die off.

So this is a plant that positively benefits from fire, and an ecosystem that only works if fires are frequent - too long without fire and the oak trees take over. While the pine trees are the most obvious beneficiaries of conflagration, they aren't the only ones; other plants have also adapted to take advantage of the nature of the environment, such as the wiregrass that dominates the forest floor. Local forestry services are aware of this, and often deliberately set controlled fires at regular intervals in order to preserve the landscape.

Among the many animals that inhabit these forests are bats. These are generally tree-roosting, rather than cave-roosting species, but, compared with other mammals, have the advantage of being able to fly away from, or at least above, any approaching fire. So they aren't too bothered by the immediate effects of fire, so long as things don't get too far out of control. But, longer term, does it really make a difference to them whether the forest burns or not? In a recent study, David Armitage and Holly Ober, of the University of Florida, looked at how bats used local forests that either were, or were not, subject to regular controlled burning.

There are a number of species of bat in these woodlands, but the most common are big brown bats (Eptesicus fuscus). These are members of the vesper bat family, and are a very common and widespread species, being found across the USA, Mexico, the Caribbean, and Central America, as well as parts of Canada, Colombia, and Venezuela. Given that vast range, they clearly aren't very fussy about where they live, and they certainly aren't specifically adapted to fiery sandhill environments.

Yet, what the study found was that big brown bats were significantly more active in forests that were burned every year or two, than they were in those that had left to grow without fire for eight years or more. They weren't alone, because most other common species of bat in the area, such as the northern yellow bat (Laisurus intermedius) showed the same preference. Is there just something about such forests that bats prefer? Evidently not, because there were some exceptions; bat species that really didn't care how frequent the fires were. So what's the difference - what's so good about a forest fire, and why is it only good for some species, and not for others?

Clearly there has to be some difference between the burned and the untouched forests that's affecting the bats. There are many reasons why an animal species might prefer one sort of environment over another. For example, there may be more places to sleep or raise young, there may be more food, or it may have some physical properties that make it easier for them to exploit. So the study looked at how the forests differed from one another.

The results here were, perhaps, not terribly surprising. Untouched forests were well on their way to transforming into dense oak woodland. They had more oak trees, more medium-sized bushes, and a thicker, and lower, forest canopy, due to the wider leaves and lower branches of the oaks compared with the pines. The forest floor also had more leaf litter and less ash, which, in time, would lead to the soil becoming more fertile, and less of the kind of sandy material that longleaf pines prefer. Indeed, since leaf litter is so flammable, if the untouched forests ever did burn, the destruction would probably be greater; the very patchiness of it on the sandhills may mean that the fires do less damage to local plants and wildlife than you might expect.

However, it's unlikely that this gives the bats more places to rest. If anything, the reverse should be the case, and earlier studies have shown that there are less places for bats to sleep in recently burned forest. So what about food? The bats aren't eating the plants, they are, like many bats, hunting for flying insects using their aerial sonar. Indeed, it was these calls that the researchers used to count the bats, identifying the different species by the different sounds that they make while searching for food. But, from trapping studies, it turned out that the insects - mostly beetles and moths, both of which the bats find tasty - were just as common in both types of woodland. The bats might care about how recent the last fire was, but the insects they prey on evidently didn't.

Which clearly gives an advantage to those bats that were equally happy to hunt in either type of forest. In the older, more untouched forests, they could search for food without having to compete with the big brown bats and others that avoided such areas, all of which were otherwise more common throughout the local area. The study found the most common of these bats were eastern pipistrelles (Perimyotis subflavus). Like the big brown bats, they are members of the vesper bat family, and they eat much the same food.

High aspect ratio (common swift)

But there is an important difference between eastern pipistrelles and big brown bats, that turns out to be key: their wings are a different shape. Big brown bats have relatively long, slender wings, described in aerodynamic terms as having a high "aspect ratio". This reduces drag when in flight, allowing the bat to fly more swiftly and to soar through the air with relative ease. As extreme cases outside the world of mammals, birds such as swifts and swallows have particularly high wing aspect ratios, and are noted for their fast, soaring flight.

Eastern pipistrelles, on the other hand, have broader, shorter, wings, relative to their body size. This gives them a low wing aspect ratio, but it also means that the wings are relatively large for the animal's body weight, giving them increased lift. That means that, while they cannot fly as fast, or as effortlessly, they are much more manoeuvrable in the air, able to rapidly change direction by tilting their wings.

The same pattern turns out to be true across all local bat species. Those with medium to high wing aspect ratio, such as big brown bats and northern yellow bats, prefer the recently burned forests, while those with low wing aspect ratios, such as eastern pipistrelles and and evening bats (Nycticeius humeralis), were just at home in the untouched forests. In short, the denser, more oak-dominated forests that had avoided wildfire, were so full of branches and leaves that the big brown bats would have had difficulty avoiding crashing into things all the time. But the eastern pipistrelles, with their more manoeuvrable flight, had no such problem, being able to dodge out of the way of thick underbrush or low hanging branches.

Low aspect ratio (common cuckoo)

In fact, we find that the big brown bats are just as happy to soar above the treetops of the untouched forests as they are above anything else. What they avoid is flying lower down, amidst all the branches. They like the fire-affected woodlands, because they are more open, allowing them to soar away to their heart's content, even below the forest canopy - which is, in any case, rather higher up in such forests.

Such findings can be important for conservation. It was already clear that, to preserve the natural habitat of sandhill forests, every now and then, you have to burn them. But, from this study, it's clear that you don't want to burn all of them. The big brown bats may love the regularly burned forests, but the eastern pipistrelles, among others, need denser forest where they can forage without interference, even though the more open woodland clearly isn't a problem for them. We need diversity, a mixed and complex environment in which a range of different species can prosper.

Burn the forests, every now and then, because, oddly enough, they do need it. Just don't burn all of them.

[Pictures by Jim Conrad, Paweł Kuźniar, and Chris Romeiks, from Wikimedia Commons]

Weasels up Trees: Pine and Beech Martens

2012-02-19T13:45:00.000Z

Pine marten

In my survey of the weasel family, I have so far looked at the mustelines; those members of the family that are most closely related to the weasels themselves. Aside from the numerous kinds of "true" weasel, this has included stoats, polecats, and mink, but, of course, the mustelines are not the only members of the weasel family. It is now time to turn to a second grouping within the family, the marten-like animals.

The oldest fossil martens date from the Pliocene; the epoch immediately before the great Pleistocene Ice Ages. By this time, they had already begun to develop some of their distinctive features. Martens are much larger than true weasels, and within, or slightly above, the size range of the largest mustelines, the European polecats. Where mustelines have evolved narrow bodies for chasing prey down into their burrows, the martens have never needed to do so, and while they have the short legs typical of most members of the family, their bodies are noticeably more compact. They are generally brown in colour, and most species have a highly visible 'bib' of paler - usually yellowish - fur on their chest.

The most distinctive feature of the martens is that they spend much of their lives in the trees, quite a different habitat from other members of the family. By heading up into the trees, they have been able to find a source of food quite away from their ground-dwelling kin, and over much of their range (although by no means all), they are the only small carnivores that hunt among the branches.

Their adaptations for the arboreal life include hairy paws with long, semi-retractile claws, giving them a good grip on branches. Indeed, the whole shape of their feet is different from that of true weasels. The latter are "digitigrade", walking on tip toe, as cats and dogs do. Being digitigrade gives an animal speed, a useful feature in a carnivore that must sometimes chase its prey, but it means that only a small part of the foot is in contact with the ground. That's not an issue for an animal on a steady surface, but grip is especially important to martens. As a result, while they don't walk fully on the soles of their feet as humans or bears do, and often rise into a digitigrade stance while running along the ground, their feet are arranged so that they can at least partially use their furry soles to better clasp onto branches when they need to.

Martens also have long, bushy, tails, and this, too, is an adaptation to their chosen lifestyle. The tail acts as a counterbalance while moving swiftly along or between branches, aided by the fact that their bodies are less elongated than those of weasels. Taken together, these features enable martens to perform remarkable feats of athleticism, leaping from branch to branch with great alacrity.

Perhaps the best known marten is the pine marten (Martes martes). Despite their name, pine martens are as at home in broadleaf deciduous forest as they are in pine forest, and they are found almost everywhere in Europe that there is sufficient woodland, avoiding only the drier Mediterranean climates of Greece, southern Portugal, and most of Spain. They are, however, found on many of the Mediterranean islands, including Sicily, Sardinia, Corisca, and the Balearic Islands. It's possible that they were introduced to these islands by humans, and have prospered there largely because there's nothing native there that's any better a dry woodland carnivore than they are, even if it isn't an ideal environment for them. On the other hand, it has been argued that the pine martens of Minorca are distinct enough to be considered their own subspecies, which would imply that they have been there a very long time indeed.

Outside of Europe, pine martens are found across Turkey, and as far east as the more fertile parts of eastern Iraq and northern Iran. Less surprisingly, perhaps, they also inhabit the forested slopes of the Caucasus Mountains and the great woodlands of northwestern Russia.

Although pine martens need forest to survive, they don't like the woodland to be too dense. Instead, they prefer a more open habitat, with sizeable gaps between at least some of the trees, allowing enough sunlight to filter down to the forest floor to encourage a dense undergrowth to form. That's because pine martens don't just hunt in the trees, but also on the ground. While their favourite food always seems to be rodents, for example, in parts of their range they eat more voles than squirrels.

Indeed, in general, pine martens seem to be quite adaptable animals, and what they eat depends a lot on where they are. They are also willing to change their diet throughout the year, taking advantage of what's available. They are less purely carnivorous than weasels, and, in parts of their range will switch to eating fruit in the autumn. During winter, they are more likely to eat carrion, or even earthworms, and they may prefer insects in the spring. In some places, they will take a lot of birds, while in others, there are sufficient rodents for birds simply not to be worth the effort, although they will still take the occasional one - or their eggs - if a good opportunity presents itself.

Pine martens are nocturnal, spending most of the day sleeping in cozy dens made inside tree hollows or other locations safely off the ground. Like most members of the weasel family, they are fairly antisocial outside of the breeding season, jealously marking out a patch of forest about five kilometres across for their own use, and driving out any adult members of their own sex that they find there. The territory is marked out with dung and with scent from their anal glands, and will include a number of hidden food caches, in addition to their favoured sleeping den.

Pine martens mate in the summer, but, like many weasels, the embryos do not begin to develop until much later, allowing them to be born eight months after conception, in the spring, when food is abundant. Litters of between three and five pups are common, although they can be larger. The young don't open their eyes for about six weeks, but begin weaning only shortly after that, eventually leaving their mother in the autumn, to find a home of their own.

American marten

Given their adaptability, it's no surprise that pine martens have spread far and wide in the past. At one point, probably during the Ice Ages, a close relative of the pine marten travelled across the forested lands of Beringia, and found itself in North America. Once the Bering Straits rose, they became cut off from their relatives in Asia, and developed into a new species. This animal, the American marten (Martes americana), is the one that Americans know as the "pine marten", and, indeed, it does look remarkably similar to its European cousin.

The American marten is, however, smaller than European pine martens; not counting the tail, the latter can be nearly two feet long (55 cm), whereas American martens never exceed a foot and a half (45 cm), and are often smaller. Their fur is somewhat richer in colour, with the yellowish throat 'bib' of pine martens sometimes turning to a brighter, orange, hue in American martens. Even though their litters don't seem to be any larger, another difference is that the females have eight teats, rather than just four.

Unlike the European species, while they can tolerate other forms of woodland, they greatly prefer coniferous forests, something that has restricted their advance southwards. They are found across much of Canada and Alaska, reaching as far east as Newfoundland, and venture into the north of Maine, Michigan and Minnesota. In the west of the USA, however, the pine forests of the Rocky Mountains have allowed them to reach much further south, and they are found as far afield as northern California and Colorado. Some researchers have even considered the martens of the US Rockies to constitute a separate species, although this has yet to be widely accepted.

In most other respects, the biology and habits of American martens are very similar to those European pine martens. They breed and give birth at around the same time, age at about the same rate, and have the same sort of social system. They do seem to rely less on fruit and the like to supplement their meat diet, which consists largely of squirrels, chipmunks, voles and, where they can get them, hares, but they, too, can be fairly said to be omnivores. They are also more likely to den on the ground that pine martens, often finding rocky crevices or other shelter, rather than tree hollows.

That trend is, however, taken much further by the beech marten (Martes foina), to the extent that it's just as commonly known by the alternative name of stone marten. Beech martens are also forest dwelling animals, and are found across much of Europe, but they seem to actively avoid pine forests, and so are absent from much of Scandinavia (except Denmark) as well as the British Isles. Their ability to tolerate drier, rockier, terrain puts them in better stead in the Mediterranean, where they are found across Spain, Portugal, and Greece, as well as in those areas frequented by pine martens. Although there are evidently many broad-leaf forests in which both species can prosper, pine martens probably only survive on the islands of the western Mediterranean because beech martens are absent there. The two species are found together in the Caucasus and many parts of the Middle East, but beech martens have also spread much further, and are common as far afield as Mongolia and Tibet.

Pine and beech martens are not easy to tell apart. In theory, beech martens are supposed to have darker fur, with a white, rather than a yellowish, bib. In practice, both species show considerable variation, and there can be a fair degree of overlap in appearance. The best way to tell them apart is by examining the third molars in their upper jaws, which have a different shape - but that's far from practical under most circumstances.

Beech marten

Although they can and do climb trees, beech martens are less eager to do so than pine martens, and they are equally happy in rocky, relatively open terrain, so long as there is adequate underbrush for tasty rodents to inhabit. They do sometimes den in trees, but more commonly in rocky crevices or the abandoned burrows of other animals (which are often abandoned because the beech marten just ate the original occupant). Generally tolerant of humans, they are even found in towns and suburban areas, where they can nest in attics or other manmade structures. This can be something of a nuisance, since they have no respect for such thing as loft insulation, and have even been reported climbing into car engines to rip up or chew the components. The fact that they can inhabit parts of human habitation has led to some referring to them as "house martens"... a name with an obvious potential for confusion.

Although their forest habitats are endangered by logging and encroaching farmland - beech martens may quite like houses, but they do avoid open fields - like many other members of the weasel family, all three species of pine and beech marten are hunted for their fur. Here, beech martens have something of an advantage, since their fur is coarser and less valuable than that of either of the pine martens, which may explain their preference for slightly warmer climates. While pine martens don't turn white over winter, as stoats do, their fur does become exceptionally thick and luxuriant before the snow arrives, something that has made them favoured targets for hunters since at least the middle stone age.

Over the last few decades, trapping of martens has become less common, and, despite low populations early in the twentieth century, none of the species are currently in any danger of extinction. Locally, problems may be more severe, especially on islands where populations were already restricted. Pine martens once ranged freely across the British Isles, but they are now all but vanished from England and Wales, and only found patchily in Ireland. In contrast, modern forestry practices in Scotland seem to have favoured them, and they are making something of a comeback there, as they are in some other parts of their range on the continent.

In one instance, martens have used their value to humans to exploit a new habitat. In the 1940s, some beech martens escaped from a fur farm near Milwaukee, and their descendants now live wild in the forests of Wisconsin, thousands of miles from their European and Asian homelands.

[Pictures from Wikimedia Commons. Cladogram adapted from Koepfli et al. 2008.]

The Lonely Koala

2012-02-12T13:01:00.000Z

The koala (Phascolarctos cinereus) is, by many standards, a fairly odd animal. Like most medium to large Australian marsupials, it is herbivorous, but it goes further than that by eating nothing but eucalypt leaves, which are not only low in nutrients, but actually poisonous. Presumably, they do this simply because nothing else does, which means that food should always be available, and they deals with the low nutrient content by spending around two thirds of their life snoozing, and with the poison with unusually efficient detoxifying liver enzymes. Like horses, they are hind-gut fermenters, which also helps them to extract what nutrition they can from food that, frankly, isn't very good.

Koalas have no close living relatives. There is only one living species (with no subspecies), and its considered different enough from everything else to be given its own family - one of a number of mammalian "families" that contain just one species. It's now agreed that the closest relatives koalas do have are the wombats, and even a brief glance at the respective animals tells you that they can't be that close.

So the only opportunity we have for really unravelling the history of koalas comes from examining fossils. For, while koalas are the only member of their family alive today, there were, of course, others in the past. But, still, not terribly many. Some other single-species families, such as that of the pronghorn antelope, represent the last surviving member of a group that was one much larger. Once, there were lots of species of North American antelope, many of them pretty weird to modern eyes, but now only the pronghorn remain, a solitary reminder of a once more diverse group.

Koalas, on the other hand, never seem to have been very numerous. The oldest remains of the living species date back to the beginning of the Ice Ages; while Australia was never covered with huge glaciers, the climate would have changed at around that time, and that may be connected with the emergence of modern koalas. Still, for much of that time, our familiar koala had at least two close relatives in the Australian forests. One of these was the giant koala (Phascolarctos stirtoni), which died out around 50,000 years ago, not long before humans reached the continent. It reached about twice the weight of the living species, which, arguably, isn't all that giant, but is still pretty big for a koala.

Most of the fossil species, however, are much older, dating back to the late Oligocene or early Miocene. At least eight species have been described from that time, although there are probably more. One of the better known is Litokoala from the early Miocene of Queensland. Only around half the size of modern koalas, there are indications from the animal's teeth that, while certainly herbivorous, they ate more than just eucalypt leaves, something that is probably true in general of early koala species.

However, even these older fossils are pretty identifiably koalas and not, for example, wombats. A new analysis by Karen Black and co-workers, of the University of New South Wales, looked at all the known species of fossil koala to try and put them into a clear framework. They also described a new species, Priscakoala lucyturnbullae (the first half of the name means simply "ancient koala") from the early Miocene of Queensland. The new fossil is just a portion of the upper jaw, and some scattered teeth from the lower jaw, but that may be more useful than it sounds, because teeth are often useful features in determining the precise differences between fossil species.

The jaw in question is about the same size as that in living koalas, so, assuming they had roughly the same bodily proportions, the rest of the animal probably was, too. Which makes it much larger than the contemporary Litokoala, and presumably the largest tree-dwelling herbivore in those particular forests. Because koalas have such a strange diet, their cheek teeth are fairly distinctive, but those on this species, while similar, lacked the shearing blades that modern (and most other fossil) koalas develop from a life-time of chewing tough leaves. So, presumably, they ate something softer - most likely still leaves, but perhaps the softer, more nutritious ones of tropical rainforest trees, rather than the tough fibrous leaves of eucalypts.

Indeed, especially given what we know of the climate of the day, it is likely that all early koalas lived in tropical rainforest, and that they switched to eucalypts as the climate changed and Australia became the drier place that (most of) it is today. While they seem to have switched to their new diet early on in the Miocene, at least some rainforest koalas lived on, because we know of one species that survived right through until the Pleistocene.

As for the overall analysis of the koala family, that showed that Priscakoala may be its most primitive known member. However, since it certainly isn't the oldest, that means it must represent an early branch in the koala family tree, one that found a comfortable niche in which to survive, even as its kin went on to explore new habitats. The analysis also looked at the enigmatic genus Koobor.

The name "koobor" is an aboriginal word for "koala", and that is originally what these animals were thought to be. Unfortunately, the key defining traits that would confirm this belong to a part of the skeleton that just isn't included in the few fossil remains we have, and there has been considerable debate about whether Koobor is a koala at all, or a member of some family of koala or wombat-like animals that are now entirely extinct. The new study seems to show that it it, indeed, a koala, albeit a primitive one, but without more complete remains, it's still hard to know how accurate that is.

Part of the problem is that, according to our best guess, the first koalas appeared about 40 million years ago, during the late Eocene. But there are no good fossil beds in Australia from that time period, leaving the earliest history of the koalas - and, for that matter, the wombats - shrouded in mystery. What we do know, however, is that when multiple species of koala did live at the same time they did not, by and large, live in the same place. There are a few exceptions, but, for the most part, any given forest only had one species of koala in it.

The different koalas of the past apparently specialised in particular types of forest, even if their diet was not quite as restricted as their modern day counterparts. As Australia dried out, and the eucalypt forests took over, only the species adapted to that type of woodland survived. Given that perspective, the existence of just one species of koala in the modern world is, perhaps, not so surprising.

[Picture from by "Fir0002" from Wikimedia Commons.]

What Fur Seals do at Sea

2012-02-05T13:19:00.000Z

I seem to have done quite a few posts on cetaceans over the last few months, and have discussed, among other things, the difficulty of finding out what they're up to, compared with land animals. But, of course, whales and dolphins are not the only fully marine mammals. There are, in fact, four groups of such mammals, with the second largest, after the cetaceans, being the pinnipeds - seals and their relatives.

Seals differ from whales and dolphins in that, while they spend almost their entire lives at sea, they still have to come onshore to breed and give birth. Mammals have an advantage over birds, and most reptiles, in that they don't lay eggs, which would drown if you tried to lay them underwater, but it's still quite difficult for newborn, air-breathing, young to immediately take to swimming. Whales and dolphins have mastered this evolutionary trick (as have sea snakes, for that matter), but seals have yet to do so. Give them a few more million years, perhaps.

However, when they're on land, in their breeding colonies, seals are relatively easy to observe, and a lot of what we know about their habits concerns that time of the year when they're busy mating and giving birth. But this, of course, is something they do for only a few weeks each year. What are they doing the rest of the time?

The South American fur seal (Arctocephalus australis) belongs to the same family as the sea lions, rather than that of most other seals. The primary distinction between these two families is the shape of the legs. While their feet are flipper shaped, the legs of fur seals and sea lions are still capable of walking, allowing them to at least waddle on land, rather than just flopping about. The downside of that is that their hind legs are less useful for swimming, so that they propel themselves through the water mainly with their fore-flippers, unlike the "true" or "earless" seals, which can make more effective use of their whole bodies.

S American   Galapagos   New Zealand
Fur Seal    Fur Seal     Fur Seal
| | |
    |           |             |     Antarctic
------------- | Fur Seal, etc.
          |                   |         ^
| |     |    Guadelupe
          ---------------------         |    Fur Seal, etc.
| |    ^
                    |                   |          |        Sea
                    ---------------------          |       Lions
                              |                    |         ^
                              |                    |         |
                              ----------------------         |
                                        |                    |
                                        |                    |
                                        ----------------------
                                                  |
                                                  |

The relationship between fur seals and sea lions is rather more complicated than the above implies. For example, the sea lions are not a single group of animals, but rather a collection of members of the "eared" seal family that aren't fur seals. Most notably, the sole northern hemisphere species of fur seal is unrelated to its southern namesakes, and represents an even older evolutionary branch than the lowest one on this chart.

South American fur seals live off the coast of South America, south of the tropics, along both the Atlantic and Pacific coasts. They are capable of travelling some distance out to sea, and evidently finding food there, but they generally prefer shallower waters close to the coast. Nonetheless, they avoid the coast itself, and only come ashore to breed. Even then, they prefer offshore islands rather than the mainland coast, presumably because they get less disturbance there.

Mariela Dassis and co-workers, of the University of Mar del Plata, watched the local fur seals to see how they used the nearby coastal waters. This particular population of fur seals breeds further north, on islands off the coast of Uruguay, but, between May and December they head south and frequent a cluster of rocky reefs close by the University's location. The reefs obviously offer them some protection that the main shoreline doesn't, whether it's shelter from the weather or just avoiding pesky humans, since only small boats can navigate the reefs, and then, only in good conditions. On the other hand, the reefs are pretty steep, making it difficult for the seals to pull themselves up onto ledges, and forcing most of them to spend their entire time swimming, just as they would do if they were further out at sea. But, with the closest reef only a few hundred metres offshore, it's quite possible for researchers to watch what they're up to by simply standing on the nearest headland with a pair of binoculars.

Unlike whales, while seals can hold their breath for longer than humans, they cannot do so for hours at a time. The fur seals in this colony seemed to spend relatively little time feeding, something that's generally true of carnivores. For the most part, they stayed very close to the reefs, exploring an area of only four square kilometres (1.5 square miles), and spending half their time in an even tinier area at the heart of that. This behaviour is fairly typical for most mammals on land, and, in this case, is likely to be associated with where their food of mackerel and other shallow-water fish was most concentrated. Indeed, while they certainly can eat deeper water fish (such as anchovies), these particular fur seals chose not to venture into water deeper than about ten metres (30 feet), evidently preferring the rocky shallows.

If they spend little time feeding or diving, what do they do all day? In fair weather, the answer seems to be mainly laying about on their backs with their flippers in the air, something they could quite happily do for hours at a time. Very occasionally, some of the larger males would haul themselves out onto a rock, but for the most part generally lazing about in the water seems to be their preferred activity when they aren't hungry. It's doubtless a good way od saving energy, and perhaps of letting their dinner settle.

While choppy seas didn't entirely convince them to stop lazing about, when the weather got breezy, they did spend more time with their heads just below the water, or actively swimming in a particular direction, perhaps to stop being washed about by wind-driven surface currents. Some of this time they may have spent looking for food, but its notable that they tried to use the reefs for shelter, staying out of the worst of the weather. Being battered about by surface waves is presumably quite exhausting, and, since they do need to breathe every now and then, staying just below the surface may be the most comfortable place to be. (We don't, incidentally, know what they did when real gales sprung up, since nobody could see them through the spray when the weather got that bad).

Factors such as the direction of surface currents also affected where the fur seals chose to spend their day, which all helps to build up a picture of how the animals interact with their ever-changing environment. That they prefer to spend their time in specific areas, for example, rather than wandering willy-nilly over the empty expanse of the sea, may have relevance for their conservation. Not, it has to be said, that South American fur seals are in any real danger, but some of their close relatives are, and an understanding of what they're doing - and, crucially, where they're doing it - when they aren't breeding can help prevent things getting any worse.

To us, the sea may look fairly similar everywhere, but to fur seals, its evidently more complicated.

[Picture by Mirko Thiessen, from Wikimedia Commons, cladogram adapted from Higdon et al, 2007]

The Red Queen and the Court Jester

2012-01-28T13:37:00.000Z

Greater blind mole rat

What is the primary driving force behind evolution? If an animal is well suited to its environment, and able to reproduce effectively, then why does it change over time? Why, in short, don't humans still live up trees, where monkeys are still perfectly happy today?

There are two broad types of explanation for what drives evolution: they're called the Red Queen and the Court Jester. It's important to note that there's no reason why they can't both be responsible. Indeed, it would be astonishing if they weren't. The debate, then, hinges on which is more important, and when.

The Red Queen hypothesis, first formalised in the 1970s, is named for the character in Through the Looking Glass, who had to run as fast as she could, just to stay still. The idea is that no animal (or other living organism) is alone, and, if you don't evolve, the creatures around you will, and you'll be doomed. One species may be very good at eating a particular type of plant, for instance, but if another species gets slightly better at doing the same thing, if the first species doesn't improve, it will be out-competed and go extinct. You always have to be better than your competitors, and they have to try to be better than you, leading to a constant drive for change - towards better adaptation to your environment and chosen food source, whatever that may be.

It's not just competitors for the same food that you have to worry about, either. It's in the interests of your food not to be eaten, so it, too, is constantly evolving ways to stop you eating it. If some food is harder to eat than others, then soon, that's all that will be left, and then the local animals have to evolve some way of eating it, or they will starve.

Another common example of the Red Queen hypothesis applies to parasites and their hosts. A parasite doesn't want to kill the animal it lives in, because it needs it to survive, but the host has no such qualms towards the parasite. Because being riddled with parasites is a bad thing, host animals that evolve better ways of fighting them off are more likely to survive. But parasites that evolve better ways of defending themselves are also more likely to survive, leading to a never-ending arms race that pushes evolution ever onwards.

This may even explain why male mammals exist. If all an animal needed to do was make exact copies of itself, it would only need females, in order to give birth. But, by mating with males, genes are constantly being reshuffled each generation, trying out different combinations, in order to frustrate parasites, which would much prefer, like a computer virus, that everyone was running an identical copy of Windows. No two animals being identical provides the raw material on which evolution can work.

This has never been the only explanation for what's going on, but it was only around ten years ago that the term "Court Jester hypothesis" was coined to describe the alternative. It's not named after any jester in particular, but just a term that sounds good in contrast to "Red Queen". The idea here is that the main driving force behind evolutionary change is random events, outside the biological realm.

That's because, while an animal may be very well suited to its environment, that's not much use if the environment changes. Change is imposed from outside, for whatever reason, and if you don't evolve to fit the new circumstances, then you will die out, and something else will take your place. Perhaps the most dramatic example is the asteroid strike that wiped out the dinosaurs. The strike itself, and the consequent widespread destruction, left the world wide open for the mammals, and they rapidly evolved to take advantage of their good fortune, taking over environments that they'd never previously had a chance to colonise.

A more recent example might be the Ice Ages. Here again, we have dramatic changes to the world that have nothing to do with biology, yet which will have forced animals to adapt or die. It's not just the advance of the massive ice sheets themselves; with the whole world cooling, swathes of tundra and pine forest shifted south, ahead of the glaciers. Animals previously living in a Mediterranean climate, for instance, suddenly found things much colder. True, they could flee south, but only if seas or mountains weren't in the way, and, even then, they'd have to be displacing something, and probably moving into an environment that wasn't identical with their old one - the vagaries of geography being what they are.

The cold need not even affect the animals directly; if you don't mind the cold, but your food does, and dies off where you live, you're still going to have to either move or adapt. Through much of the Ice Ages, animals survived by finding "refugia", isolated regions where they could cling on until the warm weather returned, but where they would be isolated from their kin, unable to mix their genes, and perhaps even forming a new species or subspecies as a result.

Of course, both hypotheses are correct, at least in general. Animals do not live in isolation, and the non-biological environment does throw the occasional surprise into the mix. Which predominates may depend, not just on what group of animals we're talking about, but also the time scale we're looking at. For instance, the Red Queen may be more important for small evolutionary changes, where even a few generations can make a difference, while the Court Jester may have more of a role to play when we're looking at larger, bur rarer, events.

It is within this context that we have to look at a newly published paper on the evolution of the blind mole rats. When I previously discussed this animal, I stated there are almost certainly more species than we know about, partly because they're quite good at hiding underground, and partly because they tend to look fairly similar. Yarin Hadid of the University of Haifa, and co-workers, examined genetic samples from 41 blind mole rats, many of which they suspected might belong to previously unidentified species. The evolutionary tree they uncovered look like this:

   Nehring's     Lesser blind
blind mole rat    mole rat
|               |    "S. vasvarii"
      |               |          |
      -----------------          |    Palestinian blind
             |                   |      mole rat, etc.
   A     |    ^
             |                   |            |    Greater blind
             ---------------------            | mole rat,
                       |                      |      etc.
   B                      |         ^
                       |                      |         |
                       ------------------------         |
                                  |                     |
      C                     |
                                  |                     |
                                  -----------------------
                                             |
             D
                                             |

Looking at the full tree in more detail, we can see a number of interesting features. The Palestinian blind mole rat (Spalax ehrenbergi) had, fairly recently, been identified as actually representing at least four different species, inhabiting places such as the Golan Heights, Galilee, and the Judean Mountains. This analysis confirmed that, but also shows that there are at least four others, and that, at least at the genetic level, they are pretty distinct from one another. So far, none of these new species (assuming they hold up to scrutiny) have yet been named, something that can be a tortuous process.

The existing status of the greater blind mole rat (Spalax microphthalmus) and its kin looks secure, but the picture for the others looks far more confused. There's at least one new species in there (Spalax vasvarii, which, so far as I can tell, was previously thought to be a subspecies of Nehring's blind mole rat), and probably more, but there's little consistent pattern to how they differ. That highlights a problem that can arise with evolutionary trees - real world nature isn't always that neat.

You might think that, when two species diverge, that's an end of the matter, and they go their separate ways from then on. And that's what evolutionary trees like the one above show, and what the computer programs that construct them are designed to find. But, in reality, two species can interbreed again some time after they separate, perhaps merging again for a short while before they re-split. That leaves a complicated genetic pattern, with one species having obtained some of its genes from the other, without having evolved them itself. That seems to be what has happened here, probably more than once, and it's quite likely impossible to ever disentangle it, making it difficult to decide what should, and should not, count as a full species.

So what does this have to do with the Red Queen and the Court Jester? Well, the researchers went on to try and time the various splits in the tree, assuming a constant rate of evolution within the group, and using the oldest known fossil that can be confidently placed at point "C" in the diagram above to calibrate the dates. They argue that when they did this, a pattern emerged. Rather than new species appearing at random points in time, they tended to do so at 100,000 year intervals, matching times when Earth's orbital eccentricity reaches a maximum, with attendant effects on the global climate. Evidence that is, for the Court Jester hypothesis.

The argument runs that, since blind mole rats are steppe-living animals, the alternate advances of coniferous forest and dry deserts could both have affected their survival, presumably by giving them less of their preferred food. But, personally, I'm not quite so convinced. Certainly, the evidence shows that the different species diversified very rapidly, over time scales of less than 200,000 years, but how strong the claimed pattern is, I'm not so sure. It's consistent with the Court Jester being behind it all, yes, but I don't know how strong it is as proof.

Be that as it may, there are still some interesting dates that pop out of the figures, and show that the Court Jester has probably been at play at least a few times, whether or not he's always the main culprit. For example, take split "A" on the chart, that between the lesser and Nehring's blind mole rats. The analysis dates that to 2.7 million years ago, around the time that the Bosporus and Dardanelles were last flooded. Significantly, today, the lesser blind mole rat (S. leucodon) lives only in the Balkans, while Nehring's blind mole rat (S. nehringi) lives only in Anatolia, on the other side of the straits. So the purely geological events linking the Black Sea to the Mediterranean may have led to the creation of two different species from a single ancestor that wandered happily between Greece and Anatolian Turkey.

Similarly, point "B", at 3.1 million years ago, and point "C" at 4.7 million years ago, correspond roughly with the creation of the Taurus and East Anatolian mountains respectively, opening up new highland habitats and creating rain shadows elsewhere that changed the local climate. And, if point "A" corresponds to the last time the Bosporus and Dardanelles opened, point "D", at 7.6 million years ago, may correspond to the first time that happened - although, in this case, the effects would have been obscured during the time that they were closed again. Heading even further back, the study suggests that the very first blind mole rats should have evolved around 20 million years ago, which is, indeed, the age of their earliest known fossils, and agrees with earlier studies.

The Court Jester may, or may not, have played his pranks using the Ice Ages, but he has plenty of other tools at his disposal.

[Picture by Vivan755, from Wikimedia Commons. Cladogram adapted from Hadid et al. 2012.]

News in Brief #3

2012-01-26T18:17:00.000Z

The Mandrill's Face

There are a number of colourful primates, but one of the more instantly recognisable is surely the mandrill (Mandrillus sphinx) whose adult males have strikingly blue and red faces. Under a strict definition, mandrills aren't really baboons, but they're very closely related to them, and the difference is pretty academic. Given that only the adult males have these extreme face-markings it's not surprising to learn that they are there mainly to advertise their masculinity and fitness as a potential father to female mandrills.

A study from 2005 confirmed that, yes, indeed, female mandrills find males with bright red noses to be particularly sexy. Oddly, though, until now nobody appears to have looked at what the bright blue patches on either side of the nose are for. In the new study, Julien Renoult and co-workers confirmed that the blue colour is more intense in dominant males, just as the red is. Indeed, it seems that what's really important is the contrast between the two. This suggests that, in the distant past, mandrills developed the red nose as a measure of their fitness, and the redder the nose, the more females liked them. So the noses of dominant males became ever redder... but there's only so red a nose can get. When some males began to develop a contrasting colour elsewhere on the snouts, the redness of their noses became more obvious, and, over the course of evolution, the bright blue/red contrast we see now developed.

Both colours seem to be under the control of testosterone, which would explain why they are most striking on the largest males, and it may also be relevant that both colours contrast strongly with the green of background foliage. There really isn't much else that you can mistake a male mandrill for...

Chimps and Children

Still on the subject of primates, our closest relatives are, of course, the chimpanzees and bonobos. Obviously, there are a number of differences between our species, but we also have a lot in common, and some of those commonalities can tell us something about how our own species evolved, and perhaps how it developed some of its unique traits.

A study by Giada Cordoni and Elisabetta Palagi examined how baby chimps begin to play, and how that compares to play in human children. It seems that, just as in humans, the way that young chimps play changes as they age. Like humans, chimps under the age of three are more likely to engage in solitary play, presumably to help hone their reflexes. However, very young chimps are just as likely to engage in more social play as their older fellows, whereas, in humans, it does become more common around the age of four.

In most other respects, there do seem to be striking similarities - for instance, young chimps do like to play with others of their own age, and not with other chimps that are slightly older or younger. Their games also become more complex as they age, and the way that they engage in more rough and tumble play also changes - until, that is, they become old enough to become genuinely aggressive, rather than merely playful. Just as human children are more likely to laugh when playing with others than on their own, young chimps are make more playful expressions when with engaging with others, possibly as a signal to indicate 'I don't really mean it' if play gets a little rough.

Where the Whales Hunt

Perhaps the least known and least well studied of all the families of large mammal is that of the beaked whales. Studying whales, of itself, presents problems that don't apply to most other groups of mammal, but beaked whales, in particular, are relatively rare, and don't like to visit shallow waters near land. Unlike animals such as right whales, beaked whales are true predators, feeding off relatively large prey, rather than plankton and shrimp. But, for an animal that's really large, living far out at sea, that presents the problem that most of what they want to eat is a very long way underneath them, where it's difficult to get at, or even to find.

A study by Patricia Arranz and co-workers used acoustic tags to not only follow Blainville's beaked whales (Mesoplodon densirostris) as they searched for food, but to record their sonar as they did so. That meant they could hear what the whales did, using the animals' own sonar to figure out things like the distance to the sea floor, just as the whales themselves do.

The study confirmed one thing we already knew: these whales are remarkably efficient divers. They dive to an average of about 830 metres (2700 feet) below the sea, with dives lasting around 48 minutes. Around half of that time is spent simply getting to the right depth, large because they don't seem to be able to dive straight down, as sperm whales do, but instead have to take a more gradual, sloping, descent. Considering that they can't breathe while they're diving, this must be fairly exhausting, and they have to spend spend two thirds of their day resting at the surface in between dives.

Once down there, they spend much of their time at the so-called "deep scattering layer" where most fish and other free-swimming organisms are found, with occasional forays down to the sea bed beneath. Here, they catch relatively slow-moving prey, and they apparently avoid hunting at shallower depths because the animals there tend to be more active and harder to catch. This tactic rewards them with about 30 catches per dive, which is evidently enough to keep them well fed and provides enough of a pay-off to make such difficult dives worthwhile.

Of Sea Lions and Marmots

There are a number of species of marmot, found mainly across Canada, Alaska, and Siberia. It's generally agreed that they first appeared in America - their closest relatives include, among other things, chipmunks - and only later reached Asia. By examining their genetics, we can get some insights into both how and when this expansion happened.

A phylogenetic study by Scott Steppan and co-workers examined the genetics of a range of different marmots to shed some light on their evolutionary history. They showed that the first Asian marmots appear to have separated from their relatives around 4.6 million years ago. Suddenly finding themselves in new and marmot-free lands, the colonists rapidly diversified, giving rise to several new species in a relatively short period of time. Today, each species lives in a different area of the Old World, including one species across in the Alps of Europe.

By contrast, the marmots left behind are still found in overlapping areas, with many places being home to more than one species. A particular puzzle that this study aimed to resolve was the relationship of the Olympic marmot (Marmota olympus) to its kin, with previous studies having produced contradictory results. Living only in one corner of Washington state, there had been some evidence that it was related to the nearby Vancouver Island marmot. But it seems it isn't, because that species appeared only 0.4 to 1.4 million years ago - presumably when Vancouver Island separated from the mainland - while Olympic marmots originated much earlier, 2.6 million years ago.

What seems to have happened is that Olympic marmots were once widespread across western Canada (although we do have to bear in mind that there are no fossils to prove this, so the story is still subject to revision). During the Ice Ages, some of the Olympic mountains were high enough to poke up through the ice sheets, leaving patches of land that were, ironically, more habitable than the lowlands round about. Here, the Olympic marmots clung on to life, while other Canadian marmots headed south. By the time the ice sheets melted, they were a new species, different enough from their relatives to inhabit the same lands.

A similar study looked at Steller sea lions (Eumetopias jubatus), another species found on both sides of the Bering Straits - although, in this case, along the coastlines from Japan to California. Using the methods of phylogeography, C.D. Phillips and co-workers showed that the species probably originated on the eastern side, and, indeed, the oldest fossil of a related animal does come from Japan, dating back around two million years. More significantly, perhaps, signs of past climate change had left their mark on the genetic record, showing how the species had struggled to survive at certain points. Now, that's largely cooling climate change, as the Ice Ages froze over their breeding rookeries, forcing them to move elsewhere. So it's not directly analogous to what we have today, but it does show, in general terms, how change in climate can affect the fate of species.

Sabre-tooth Kittens

Juvenile and adult Smilodon populator. Scale bar is 5 cm.

Not all fossils will be of adult animals, and its possible to tell when a skull belongs to a juvenile mammal because the bones will not have fully fused. Per Christansen of the University of Aalborg has taken advantage of this to examine how sabre-tooth cats (Smilodon spp.) changed as they aged, and compare them with how we know living big cats change.

The picture above shows how dramatic those changes were. The enlargement of the sabre-like canines is, perhaps, the most obvious change with age, but there are other alterations, such as the development of the high sagittal crest at the back of the skull, to which some of the jaw muscles would have attached. In general, this seems to mirror the changes in animals such as jaguars and leopards as they age, but they are far more dramatic. In fact, the skull of the juvenile cat does have some resemblance to that of early sabre-tooth species, long before the highly evolved Smilodon.

That's not to say that the changes during life simply echo the evolution of the animals. The changes in the skull are mostly associated with the development of increasing bite power, and some of those are visible even in the youngster. But not so many, not least because very young sabre-tooths won't have needed to bite hard; they'll have wanted to suckle from their mothers, just like any other cub.

[Mandrill image from Wikimedia Commons. Skulls from Christiansen 2012, released under the Creative Commons license].

Weasels, Weasels, Everywhere

2012-01-22T12:30:00.000Z

Long-tailed weasel

The most successful body plan within the weasel family has been that for which it is best known: the small, slender, agile carnivore that feeds on prey too small for larger predators to bother with. In Europe and Canada, the best known such animals are probably common weasels and stoats, both remarkably widespread animals across the temperate regions of the northern hemisphere. But, of course, they are far from alone, just two among a total of fourteen currently recognised species of what, for lack of a better term, we can call "true weasels".

In North America, common (or "least") weasels and stoats are found in Canada and in the northwestern and northeastern corners of the US; they generally do not venture into warmer climes, as they do in many parts of Europe and Asia. That's because, in America, there is another species of weasel better adapted to those regions. This is the long-tailed weasel (Mustela frenata), and it, not the common weasel, is the one best known in most parts of the USA.

Like it's more northerly kin, it is a highly adaptable animal, and while it may prefer relatively open, brushy areas, it is happy to live anywhere from forests to farmland. As a result, while it avoids the harshest deserts, it is found in every one of the 48 contiguous states, as well as in the Great Plains and the southwestern mountains of Canada. Not only that, but is also inhabits much of Mexico, the whole of Central America, and an arc of territory stretching from Venezuela to Bolivia. So, this is an animal that is perfectly happy in jungles, mountains, plains, or pine forests - just about anywhere it can find rodents to eat and at least a passable supply of water.

Long-tailed weasel looks much like stoats; the males are about the same size, although the females are noticeably smaller. They have a longer tail, of course, and somewhat yellowish (rather than white) underparts, and, in some parts of their range, they also have black markings on the face. They resembles stoats in many other respects, too. Where it's cold enough to be worthwhile, for instance, they moult in winter, producing a pure white coat, save for a black tip to the tail, which presumably serves to distract predators away from the more vital parts of their anatomy. Also like stoats, they breed in mid-summer, then hold the embryo in suspended animation until the following spring, so that as much food as possible is available when the mother finally gives birth.

Their small, slender body gives them a high metabolism that keeps them frenetically active, so that, while many nocturnal, they are frequently obliged to feed during the day because they burn up so many calories just staying alive. They feed mainly on rodents, spending much of their lives peeking into any hole or crevice they can squeeze into (and, given their size and shape, that's quite a few) to see if there's anything edible inside. They can, however, also take down larger prey, including rabbits, and, if there's a knothole in a hen house, domestic chickens. There does not, however, appear to be any truth in the myth that they drink the blood of their prey, except insofar as that's difficult to avoid while eating.

The white winter coat of northern long-tailed weasels is no thicker than their summer one; evidently, their small size and slender shape means that they lose heat so rapidly that this would make little difference, and instead, it's purely for camouflage against the snow. As a result, it has been suggested that watching how the geographic boundary between moulting weasels and those that stay brown all year moves, may, as the world continues to warm, give us some insights into short-term evolution. On the other hand, the pure white coat does make the animal valuable to fur trappers, and, indeed, much of the fur sold as "ermine" is actually from these creatures, and not from stoats.

Rather less is known of the other eleven species of "true" weasel, probably because none of them live in Europe or North America. They range in size from almost as small as the common weasel to nearly as large as a polecat, but they all have the same general body plan of a long, slender, torso and short legs. Most have the typical "weasel" coat pattern of a brown body with distinct, pale underparts, but there are exceptions. Although some of them do get paler in winter, none turn to pure white.

Apart from Australia and Antarctica, the only continent in which they have had little success is Africa. The only species that lives there is the Egyptian weasel (Mustela subpalmata), and that lives only in the irrigated farmlands of the lower Nile valley, in the extreme northeastern corner of the continent. We know almost nothing about it, other than that is so similar to the common weasel that it was long thought to be the same animal.

Siberian weasel

Most of the remaining species live in eastern Asia. The best studied are probably the Siberian weasels (Mustela sibirica), which are often hunted for their fur. Despite their name, they are also found in western Russia, and they are common throughout China and Korea, and can be found as far south as Laos. Sometimes called "kolinskis", they live in high altitude forests, and they are somewhat between other weasels and polecats in appearance, size, and habits, something that is born out by their apparent position on the evolutionary tree of the weasel family. Japanese weasels (Mustela itatsi) are extremely similar, and are probably close relatives; they live only on the Japanese islands.

Altai Mountain weasels (Mustela altaica) are, as their name suggests, similarly high altitude, but they prefer open alpine meadows, and, at best, only venture into the fringes of sparse woodland areas. They are found across, not just the Altai Mountains of western Mongolia, but also across other nearby mountain ranges, including the Himalayas, where they feed on mountain pikas and rodents.

Altai mountain weasel

Heading further south, we come to another mountain species, the yellow-bellied weasel (Mustela kathiah) of south China, northern India, and neighbouring regions south to Vietnam. They are apparently quite adaptable, being found from high pine forests to chilly, desolate wastelands, and even taking trips into nearby lowland areas, all of which means that they seem to be holding up quite well, despite being regularly hunted. Back-striped weasels (Mustela strigidorsa), which have a distinctive streak of pale fur down the middle of their back, live in much the same part of the world, but in jungle-covered hills, rather than in mountainous, areas. Although back-striped weasels used to be thought extremely rare, and likely endangered, it seems that they're really just good at hiding - as well they might be, in the jungle - and, so far at least, there seems no reason to suppose they're at any risk, although their body parts are sometimes used in traditional medicine.

Still in the jungles of southeast Asia, we next come to the Malaysian weasels (Mustela nudipes), living in the Malaysian peninsula, and the islands of Borneo and Sumatra. They have a particularly distinctive appearance, being about the size of a ferret, with bright reddish-brown fur over most of the body, that contrasts with a pale, or even white, face. We know very little about them, but we know even less about their close neighbours, the Indonesian mountain weasels (Mustela lutreolina), similarly large animals that live somewhere among the isolated mountain peaks of Sumatra and Java and bear a remarkable resemblance to mink - only nine individuals have ever been seen by scientists.

Back-striped weasel

All of this indicates that, while more familiar species of weasel inhabit relatively cold environments, there are many that are perfectly at home in the depths of sweltering tropical jungles. While none have penetrated that far into Africa, long-tailed weasels are not the only species in South America.

Amazon weasels (Mustela africana - although I have no idea why) live throughout the Amazon jungle, and may be descended from long-tailed weasels that moved further south. They are about the size of a stoat, with dark fur over most of the body, pale underparts, and an unusual dark stripe running down the centre of their chest and belly. What little we know of them makes them seem slightly odd, since they appear to be active mainly during the day, and to travel in small groups, whereas most weasels are nocturnal and solitary. With so few reports of the animal, however, it's difficult to tell how much of this is really typical - it's presumably quite hard to find something the size of a weasel in the jungle at night.

The most recently discovered species of weasels are the Colombian weasels (Mustela felipei), first described only in 1978. Found close to high mountain rivers on both sides of the Colombian-Ecuadorian border, they have dark brown fur with yellowish underparts. Like most tropical weasels, their feet have hairless soles, but, unusually, the toes are also webbed, like those of a mink, although the animal is far smaller, scarcely larger than a common weasel. Presumably, this means that they are semi-aquatic, but we don't have enough observations to be sure. The only "true" weasel to be officially classified as a Vulnerable species, the animal is in danger almost before we've learned anything about it.

All of the species so far mentioned are placed within the genus Mustela, the largest of all weasel genera. There is some evidence that the three American species may actually be more closely related to American mink (Neovison vison) than they are to weasels on other continents, and, if so, they will need to change their scientific name. That's entirely plausible, since it would explain where the American mink came from, but it's interesting to note that there is one weasel that's already known to be odd enough to be placed in its own genus.

Patagonian weasels (Lyncodon patagonicus) have only 28 teeth, rather than the 34 found in every other species, and they also look rather different. They have grizzled grey fur over most of the body, with dark limbs and throat and head, but with a broad white stripe across their face and neck that makes them look rather like a stoat-sized honey badger. They inhabit the open steppes and scrubby woodlands of the Argentinian interior, and parts of Chile, where they apparently feed on burrowing rodents such as tuco-tucos, and the occasional bird. It would be interesting to know how such an odd weasel came to be living so far from any of its kin. Does it represent the last survivor of an earlier migration of weasels, pre-dating the American mink and their relatives, pushed out into the southern steppes, or is it just a really aberrant member of that group? For the time being, it remains a mystery.

[Pictures of long-tailed and Altai Mountain weasels from Wikimedia Commons. Picture of back-striped weasel from glopedia.com. Picture of Siberian weasel by "coniferconifer" released under the terms of the Creative Commons 2.0 license. Cladogram adapted from Koepfli et al. 2008.]

The Time of Horned Rodents

2012-01-15T12:11:00.000Z

Ceratogaulus hatcheri

The rodents are the most successful order of mammals, with literally thousands of species worldwide. There are a number of reasons for this success, but one of them concerns the arrangement of the jaw muscles, which are modified to improve their ability to gnaw with their powerful, chisel-like teeth.

The muscle in question is the masseter, a muscle that, in humans, runs from the forward part of the cheekbone down to the back of the jaw, and which is important in chewing - it is often particularly large in herbivores, for example. It has two parts, one deep and one superficial, and in rodents, one or both of these parts extend much further forward than normal, reaching up onto the side of the snout. Generally speaking, in squirrel-like rodents, its the superficial part of the muscle that does this, in guinea pigs and their relatives, its the deep part, and in mouse-like rodents, it's both. Because the shape of the skull has to be modified to allow for these attachments, it is possible to tell which of the three possible arrangements even a fossil species had.

But there is one rodent species alive today that doesn't have any of these features. (Actually, mole rats don't have the full muscle arrangement, either, but we can tell from the shape of their skulls that their ancestors once did). That animal is the mountain beaver (Aplodontia rufa), and it's only found in the Rocky Mountains of North America. Despite the name, it is not particularly closely related to real beavers, and it doesn't look much like them, either, looking more like some kind of giant vole. Indeed, its a burrowing animal that doesn't like water, and usually only ventures above ground at night.

Although there is no question that it is a rodent, the complete lack of the muscle arrangements found in any of its relatives often result in it being described as the "most primitive living rodent." Although it seems to be more closely related to squirrels than anything else, it doesn't seem to have any particularly close relatives, and is the sole living member of its family, a rather strange animal not quite like any other rodent.

Or, at least, not like any other rodent that's alive today. Because this odd creature has to have come from somewhere, and it turns out that some of its extinct relatives were even stranger. While there are a number of fossils belonging to the mountain beaver family itself, there was also once another family of rodents belonging to the same evolutionary line, one that split from the squirrels very early on. These animals were the mylagaulids, and some of them had a feature that no other rodent has had before or since: they had horns.

Mylagaulines Other       Mountain
    Mylagaulids       Beaver
   ^       ^      |
     |             |            |
   |     |      |       Squirrels
     ---------------              |         ^
    |           |    |
|     |    | Dormice
    -----------------------    |    ^
    |           |    |
|           |    |
    -------------------------    |
      |                      |
                                  |                      |
                                  ------------------------
                                             |
                                             |

These were, like mountain beavers, burrowing animals. We can tell this from their powerful fore-claws, and because they had the sort of wedge-shaped head that is often found in animals that habitually push earth out of the way with their snouts (the golden moles being a particularly extreme example). They were quite large for rodents, being around the size of a gopher, and had small eyes, as one might expect for an animal that spends much of its time underground. Indeed, for the most part, gophers are pretty much exactly what they would have looked like.

Except, of course, that gophers do not have horns. The mylagaulids' horns were not placed on the top of their head, as in cattle or antelopes, but rather on the tips their noses, like a rhinoceros. Unlike the horns of rhinoceroses, however, these had a solid bony core, and there were two of them, side by side, each stout and conical. It's not entirely clear hat the horns were for, although it's possible that they used them to shovel earth out of the way while digging.

Not all mylogaulids had horns, and there's some dispute as to how many really did. That's partly because most of what we know of the group comes from very fragmentary fossils - many species are known only from their teeth, which obviously makes it difficult to say what the rest of the animal might have looked like. We know for certain that one genus, Ceratogaulus, had horns, because we have a fairly complete skeleton for that (you may also find mention of Epigaulus in older books - it's the same animal), but, beyond that, it's less clear. A fossil recently described by Nicholas Czaplewski of the Oklahoma Museum of Natural History may change that, however.

The horns of this fossil are different from those of any Ceratogaulus species, because of the presence of an unusual groove along the back. On the basis of the shape of its teeth, Czaplewski instead places it in the closely related genus Mylagaulus - one of the ones for which we just never had the relevant part of the skull before. If he's right, horns may be more widespread in this unusual group than we previously thought.

However, some other fossils described in the same issue of the Journal of Vertebrate Paleontology may shed more light on the origins of the group. These do not belong to a new species, but they are far more complete than previously studied specimens. Jonathon Calede of the University of Oregon and Samantha Hopkins of the Unviersity of Washington place the fossils in the species Alphagaulus pristinus, one that has a key place in the evolution of these strange animals.

The more specialised mylagaulids, including all of the horned ones, belong to a more narrowly defined group, the mylagaulines, while those outside this group tend to be earlier forms less well adapted to a burrowing lifestyle. Alphagualus pristinus is significant in that it seems to be the most primitive of the mylagaulines, representing the transition from the less specialised ancestral species to the burrowing - and eventually horned - ones.

But that was difficult to know for sure, when all we had was a few bits of jaw and some teeth. Dating from 15 or 16 million years ago, these new fossils give us a much more complete picture. The forelimbs of this animal were short and stout, and we can see the places where powerful muscles would have been attached, suitable for digging through the soil. The head is also somewhat wedge-shaped, and, while the animal did not yet have horns, the bones at the tip of the snout were especially solid, allowing for reinforcement as it shovelled its way forward. Indeed, although we can't know for sure, it's quite possible that the snout would have been covered in a horny plate, much like those of golden moles, and this later thickened to create the distinctive nose-horns.

So, the animal was well suited for burrowing, although the authors point out that its adaptations to doing so were less extreme than those in the later, horned, forms. It seems to mark a transition to a new lifestyle, and shows that - as if often the case - not all the adaptations appeared at once in the group's evolutionary history.

Significantly, however, some of the fossils belonged not to adults, but to juveniles. We can tell this because the bones in their skulls had yet to fully fuse, and, together with other differences in the skeleton, that enables to learn something about how these animals grew up. In particular, the younger specimens had less extreme adaptations than those found in the older animals, with more slender arms and a rounder head. That means that the animals became more specialised for digging as they aged, something also seen in beavers and marmots. In this way, as they grew older, becoming large enough and independent enough to start digging their own burrows, the animals mirrored the development of their own ancestors over time.

[Picture from Wikimedia Commons. Cladogram adapted from Blanga-Kanfi et al.]

The First Dolphin in the Amazon

2012-01-08T14:44:00.001Z

Tucuxi in the Orinoco River

In most of these posts, I tend to include a cladogram - a tree-like diagram showing how different animals are related to one another. But how do we know, and how are these things constructed?

Consider the dolphin family. We know that this is a true evolutionary group of animals - that is, it contains all of the descendants of some original common ancestor. We also have a pretty good idea of how it relates to other, similar, groups of animals, such as the porpoise family. But quite how the different types of dolphin are related to one another is less clear. I mentioned previously, when discussing the discovery of the burranan dolphin, just how confused we are about how bottlenose and spinner dolphins (among others) are related. But that is by no means the only unresolved issue in trying to sort out the dolphin family tree.

The tucuxi (Sotalia fluviatilis) is unique among members of the dolphin family in that it doesn't live in the sea. Instead, it lives only in freshwater, in the wide reaches of the Amazon River and its larger tributaries. It's not quite the only dolphin that habitually swims upriver, and, indeed, there are freshwater "dolphins" that aren't really members of the dolphin family at all, but it's the only "true" dolphin that avoids salt water altogether. Which makes it a pretty odd animal.

We already know that it's closest relative is the Guyanan dolphin, sometimes called the costero, an animal that inhabits shallow coastal waters and brackish estuaries from Honduras to southern Brazil. Indeed, so similar are the two animals that, until 2005, they were thought to be the same thing - it was only when we worked that they weren't that we realised the tucuxi really does avoid salt water. Clearly, at some point, the common ancestor of these species split into two populations, one staying along the coast, and the other heading inland. But quite how that common ancestor was related to any other sort of dolphin was far less clear.

Not, it has to be said, for lack of trying to find out. There are at least two suggestions: either their closest relative is the rough-toothed dolphin (Steno bredanensis), or they're closest to the three species of humpback dolphin (Sousa spp.) That's partly due to disagreements on the best way of working this sort of thing out. It's generally agreed that using physical appearance alone can be misleading (although, in the case of fossils, you don't have much alternative), and that the best way of determining relatedness is to examine the DNA of the two animals. You may have heard, for example, that humans share around 99% of their DNA with chimps. That's probably an exaggeration, but, certainly we do share more of our DNA with chimps than with anything else, which is how we know they're our closest relatives. So do the same for dolphins, and we're sorted, right?

Well, not quite, because how best to compare DNA isn't always that clear. Which is why there's dispute as to whether 99% is, or is not, the best figure for chimps and humans in the first place. For instance, do we compare the entire genome, or do we get a clearer signal if we focus on just one part of it?

In any given animal cell, the vast majority of the DNA is contained within the cell nucleus. If the animal, like mammals, reproduces sexually, about half of that DNA will come from each parent. However, outside the nucleus are, among other things, tiny structures called mitochondria. Their function is to provide energy for the cell, but crucially, they also contain a tiny amount of DNA. Because of the way that sperm fertilise the egg, they contribute nothing to the offspring's mitochondria, and so mitochondrial DNA is inherited exclusively from the mother. As a result, it has often been argued that this gives a clearer idea of evolutionary relationships, enabling you to follow them down a single line. It probably also helps that there's a lot less of it, which makes it easier to analyse and interpret any differences you may find.

Indeed, the usual approach is to compare just one mitochondrial gene, cytochrome b, which has the advantage of being found in every living thing that's capable of breathing oxygen, while still having slight differences even between closely related species. However, that's not the only approach, and that brings us back to dolphins.

In a study published in December, Haydée Cunha of the Federal University of Rio de Janeiro, and colleagues, used the full set of mitochondrial genes to try and resolve the question of the tucuxi's origins. They took skin samples from tucuxis, Guyanan dolphins, and rough-toothed dolphins, extracted the mitochondrial DNA. They then compared the DNA sequences with each other, and with those of every other species of dolphin that has had similar analysis performed in the past.

That last part isn't necessarily as easy as it might sound. You need to compare thousands of different factors between a large number of different samples, to determine not just how much they differ, but in exactly which ways. That's beyond the capability of any human being, so the data has to be crunched in a computer, generating hundreds of possible evolutionary trees, determining which one fits the data best, and then coming up with a figure for likely that one is to be correct - its a complex process, involving quite a lot of maths.

In this case, the end result was a tree that showed at least three evolutionary lines within the dolphin family. One included the bottlenose dolphins, the spinner dolphin, and assorted relatives, while another included the tucuxi, the Guyanan dolphin and... the rough-toothed dolphin. The humpback dolphins, it seemed, were easily grouped in with the bottlenoses, and the results look pretty firm on that.

However, the computer struggled to make any sense of the relationships within the bottlenose group, and it had even greater trouble sorting out the third evolutionary line. This third group clearly included the pilot whales, among others, but there were some other species - including the killer whale - that there just wasn't a clear enough signal to place. They might belong to that line, but they might be separate. Being a computer program, it did it was told to and churned out a best guess, but the odds it gave of being right were little better than 50/50.

This is why debates still continue about how some groups of animals are related, and on the precise details of the evolutionary history. Some details may be clear, but even if we can agree on a one-size-fits-all method of comparing things (which we can't) sometimes there's just too many possible answers with an equal chance of being correct. As more data comes in, revisions get made, and a consensus generally evolves, but, at least in the case of the dolphin family, we aren't there yet. More research, as they say, is needed.

However, having produced their cladogram, the researchers' next step was to generate a chronogram. While a standard cladogram tells us how things are related, a chronogram goes one step further, and tries to figure out when their last common ancestor lived. In this case, for example, that might help us to figure out why the ancestors of the tucuxi chose to abandon the sea, a place that every other "true" dolphin has been perfectly happy in.

Again, computer programs are required. The theory runs that genes accumulate mutations at a more or less constant rate, at least within a group of closely related organisms. Count the mutations, and you can work out how old the evolutionary line is. However, that supposes you have at least some idea of what the rate might be, and to get that, you need to plug some ages into the software that you're fairly confident of. For instance, the oldest known fossil porpoise, Salumiphocaena stocktoni, is around 10 million years old, so the porpoises, as a group, must be older than that. On the other hand, the oldest known member of the group that includes both dolphins and porpoises are around 23 million years old, so that's the oldest the porpoises (or dolphins) are likely to be.

Do that sort of calculation for a number of different points on your evolutionary tree, to decrease the likelihood you're not missing something (because it might be that there's a really old porpoise we haven't found yet), and the software has something to work with. In this case, here's what it produced:

Click on the image to make it larger. The blue bars show the uncertainty in the answers - you'll note that some overlap, which is why it's difficult to figure out which order some events happened in. The greenish box represents the dolphin family; Tursiops are the bottlenose dolphins, Sousa, the humpbacked dolphins, Globicephala, the pilot whales, and so on (there's a full list here).

The chart shows that the tucuxi first evolved around 2.3 million years ago, heading inland away from the ancestors of the Guyanan dolphins. That's consistent with most, though not all, previous estimates, but there's another reason to suppose that it may be correct. That's because the Amazon River first flowed around 2.5 million years ago, due to a combination of the uplift of the Andes and a worldwide drop in sea levels as the first Ice Age loomed. Which means that the tucuxi may be as old as the river it swims in, heading upstream in the wake of local changes in both climate and geography.

[Picture from Wikimedia Commons. Chronogram from Cunha et al, 2011, released under the Creative Commons licence.]

Grazers and Browsers - and how to tell them apart without watching

2011-12-18T19:35:00.000Z

Wildebeest are grazers - note the squarish muzzle

One advantage of studying the fossils of prehistoric mammals, as opposed to dinosaurs, is that mammals are still around today, while non-avian dinosaurs aren't. That gives us the ability to compare fossil species with living ones, and be fairly confident that our comparisons make sense. That's not to say, of course, that we can't infer quite a lot from the shape and structure of dinosaur bones, and work out details of their lifestyle and habits. But there's nothing much like non-avian dinosaurs around today, so there will inevitably be some guesswork involved when we do - educated guesswork, to be sure, but guesswork none the less.

Although the same can be said of fossil mammals - especially the stranger ones - in many cases, we can be more confident that our educated guesses are likely to be accurate. For example, sabre-tooth cats were, well... cats. So we can look at, for example, the proportions of their limbs, compare them with living cats, and deduce whether they were more like, say, jaguars, than they were like leopards. Because leopards, jaguars, and sabre-tooths are, in many respects, quite similar, it's pretty likely that inferences drawn from the first two will apply to the third, unless there's some good reason to suppose otherwise. We know what cats are like, and sabre-tooths were cats, so that tells us a lot.

And what about herbivores? Herbivory includes a range of different diets, such as animals that feed mainly on seeds, or fruit. But large mammalian herbivores tend to have two possible feeding strategies: grazing and browsing. The best way to tell the two apart would be by examining their dung, and, failing that, the structure of their digestive systems could well be helpful. Neither, of course, are possible, if all you have is a fossil skeleton, but, fortunately, there are other clues we can examine.

Grazing animals feed primarily on grass. Grass can be difficult to digest, which is why some animals have four-chambered stomachs, and is also wearing on the teeth, not just because grass itself is relatively tough, but because it's hard to eat it off the ground without getting at least some grit or soil in with it. But it does have the advantage of being fairly plentiful, and the fact that it's all much of a muchness - one mouthful of grass is more or less like any other. Grazing animals, such as cows and sheep, therefore tend to have relatively broad muzzles, so that they can chomp up large clumps of grass in one go.

A browsing animal, on the other hand, feeds on leaves, buds, and the like. Such food is easier to digest, so that the digestive system does not need to be quite so big (although still, generally speaking, larger and more complex than that of carnivores). However, while suitable browse is common enough in the right sort of environment, it isn't distributed in quite the same way. Leaves and so on are found in bushes and trees, not so easy to get at as grass and, crucially, mixed in with things like twigs.

The problem with twigs is that, while they certainly contain nutritious material, they also contain a lot of wood, and wood is completely indigestible. At the chemical level, wood is composed of a complex aromatic polymer, called lignin, that is neither carbohydrate, nor protein, nor fat, and, apart from termites, there are pretty much no members of the animal kingdom that can digest it. So, from a nutritional standpoint, any wood that you eat is wasted effort. Of course, some animals will eat smaller twigs and so on, to get at the sap, or other nutritious material, inside, but, generally speaking, browsing animals want to eat as little of the stuff as possible.

Which means that they don't just want to scoop up large quantities of plant matter, like grazers do - they want to be picky, aiming for the tasty looking leaves, buds and other green bits that don't have wood in them. All of which means they tend to have relatively slender snouts, that they can poke into bushes with fine precision. So, a deer, for example, tends to have a narrower head than, say, a bison.

We can extend that principle - an animal with a wide snout is more likely to be a grazer than a browser - to fossil animals in general, such as dinosaurs, but it's perhaps easier to do so when there is a direct analogue alive today, and we can make a direct comparison. There are, however, a couple of complications. Firstly, many large herbivores are both grazers and browsers, so that there are no hard and fast lines between the two. Secondly, in science we want to be precise, so we need a numerical measure of the shape of the jaw that helps us decide whether a particular fossil belonged to one or the other (or both).

There have been a number of proposals made as to how this can best be done. Most of these rely on the shape of the lower jaw, which is apparently more likely to be preserved intact than the upper. The lower jaw in large herbivorous mammals generally includes a row of incisor teeth at the front, for clipping off plant material, followed by a long, toothless gap, and then the chewing teeth at the rear, behind the snout proper, and in a part of the head more shaped by the attachments for the jaw muscles. Methods for quantifying the shape of the forward part of the jaw - the bit that's relevant here - include measuring the width just behind the row of incisors, how curved that row is, and even how the different incisors compare to each other.

A new method, proposed by Danielle Fraser and Jessica Theodore of the University of Calgary, instead compares the width of the jaw with its depth. By 'depth', I'm referring to the distance from the tip to what would be the base of the chin on a human, but which is much further back, on the underside of the snout, in the sort of animals they're looking at. And, of course, that's where the existence of close living relatives comes in useful, because we can look specifically at ruminants, which we know are broadly similar in all other respects, and ignore more distantly related herbivores, such as horses or kangaroos, and have a reasonable chance that all other factors are going to be equal.

What this means is that we can collect skulls from a range of living animals, and see how good the different measures are at predicting what they eat. It may seem logical that browsers have longer, narrower snouts, but is it really true, and if so, is it true enough to allow us to make a reasonable guess as to the diet of an animal we know only from the skeleton? Or are there other factors we need to take into account? For instance, a bison is a lot larger than a deer, and that certainly affects other aspects of their body shape, so might it affect the shape of the head, too?

Well, apparently not. Indeed, the authors conclude that, in their survey of 34 species of ruminant, the ratio of muzzle length to width was the best predictor of how the animal ate. Most of the older methods, while not useless, gave only a vague indication, and made the wrong prediction almost as often as the correct one. The only exception was a method that evaluates the shape, not of the lower jaw, but the upper one - and even that was less useful than their new method. The upper jaw of ruminants has no teeth at the front, just a tough pad against which the incisors chomp to crop food, which may make the shape of it less important than the tooth-bearing lower jaw. But, since it obviously can't be a completely different shape from the lower jaw, there would have to be some correlation even by default.

So does this method allow us, with certainty, to say that any newly discovered fossil ruminant belonged to a grazer or a browser? Hardly, even if it is the best method we have found so far. That's because of the wide range of animals that are somewhere in between, and the fact that not everything follows the general trend. For example, it turns out that hartebeest (a kind of antelope) have a narrower muzzle than you would expect, bearing in mind that they are, like cattle, grazers. Perhaps there's something different about the way they graze, but it seems as likely to me that there's some other confounding factor we haven't thought of.

What we can say, however, is that, if we have a lower jaw that shows a relatively extreme shape, similar to a wildebeest (grazer) or moose (browser), for example, that we can be fairly sure what it isn't. Given that many animals are somewhere in between, with jaw shapes correspondingly varied, we can never rule out the possibility that an animal isn't a bit of both, although perhaps with a preference in one particular direction. But, given the muddiness of real-world nature, that isn't all that bad.

So we can say something about how an animal ate, without ever having to watch it feed, or examine its dung, just from the shape of its jaws and teeth.

[Picture from Wikimedia Commons]

Synapsida will be taking a break over Christmas, but will be back in the New Year.

Weasels in the Snow: Common Weasels and Stoats

2011-12-11T12:50:00.000Z

A stoat in summer

In terms of the number of species, the weasel family is the most successful of the carnivoran families. That is, at least in part, due to their small size, allowing them to fill niches unavailable to larger animals such as bears, lions, or wolves. The members of the family that take this to the extreme are, of course, those for which it is named: the weasels themselves.

The term "weasel" isn't a truly scientific one. It's used to refer to all those musteline animals that are neither polecats, mink, nor stoats, and that isn't a natural group of animals. A true evolutionary unit should consist of a common ancestor and all of its descendants, but the term "weasel", while it would plausibly include the common ancestor, arbitrarily excludes some of that animal's descendants. In reality, therefore, the animals commonly referred to as "weasels" include some that are closer to, say, polecats, than they are to other "weasels", and, as a whole, they represent at least three, and probably four, different evolutionary lines.

The common weasel (Mustela nivalis) is the epitome of the idea that, for weasels, small is good. Known in America as the least weasel, at as little as 12 cm (5 inches) long ignoring the tail, it is the smallest member of it's family, and thus, the smallest of all carnivorans. Although it prefers forests or farmland, it is happy to live almost anywhere that there is cover, including mountains and semi-desert, and this adaptability has allowed it to inhabit a wider stretch of the world than any other carnivoran species except the wolf.

Common weasels are found throughout Europe, except for Ireland and some of the smaller islands, into North Africa, and across the whole of Asia north of the Middle East and the Himalayas, reaching as far as Japan. Nor does it stop there, for exactly the same species lives in Alaska, Canada, and across much of the Great Plains of the USA. There is, admittedly, considerable variation across this vast range with numerous subspecies and American weasels, for example, being smaller than their European cousins, but, nonetheless, the evidence seems to suggest that they are really are just one species. Even when there is debate that these may represent two or more different species, the proposed dividing line isn't across the oceans, as one might expect, but runs through the middle of Sweden - it's been argued that the weasels of most of Europe may be distinct from those of Lapland, but that the latter are still the same as those in Canada and America.

Although they are capable of taking a wide range of prey, common weasels feed almost entirely on small rodents, especially voles. Their small size and slender, sinuous bodies give them a significant advantage here, for they can pursue such animals into their burrows, scampering down narrow passages and giving their prey no means of escape. In fact, they often take over the burrows of animals they have killed, using them as their own shelter.

However, there is a price to be paid for this ability. Small animals lose body heat easily, and therefore need a faster metabolism than larger animals do, and so, proportional to their size, require a higher calorie intake. The slender bodies of weasels make this worse, because their body surface is larger, relative to their mass, than it might otherwise be, causing them to lose energy even faster.

As a result, weasels need to eat a lot. A common weasel has to eat between five and ten meals every day, and consumes up to a third of its body mass daily - and maybe twice that if it's pregnant. When you have to eat that frequently, even a long sleep isn't an option, and weasels take a number of short naps through the day. While they prefer to be nocturnal, using the cover of darkness to hide from larger carnivores that might try to eat them, their constant need for food means that they also have to be up and about for at least some of the daylight hours.

It helps that they are efficient killers, quickly dispatching prey with a powerful bite to the back of the neck. They can even take animals larger than themselves, holding on with their jaws, forcing the animal to the ground, and then raking with their claws to finish it off. While, of course, they aren't large enough to consume even a small rabbit at a single sitting, taking one down does at least fill their bellies for quite a while.

Weasels also have to be active through the winter. even at times of heavy snow. For most of the year, they have brown fur with distinct white underparts, but in much of their range, they moult in the late autumn, producing a pure white coat (or, in some places, just a paler one) that hides them against the snow, and remains until the spring. This would probably be valuable to fur trappers were it not for the fact that the common weasel is just too small for it to be worthwhile catching and skinning them. Indeed, common weasels are useful animals to have on the farm, because all of that eating helps to keep down the population of mice.

The stoat (Mustela erminea) belongs to a separate evolutionary line to the common weasel, with the two last having had a common ancestor over three million years ago, before the start of the Ice Ages. Nonetheless, the two animals are remarkably similar in both appearance and habits. Stoats are somewhat larger, with heavier bodies and longer limbs, weighing between 210 and 350 grams (7 to 12 ounces), compared with a weight of less than 100 grams (3½ ounces) for most common weasels. However, they are much the same colour, and, in some parts of the world, the largest common weasels are actually larger than the smallest stoats, so the easiest way to tell them apart is that the latter have a much longer tail, which is black for almost half its length, rather than just at the tip.

Like weasels, stoats are adaptable animals, and represent a single species found in Europe, north and central Asia, and North America, albeit with even more distinct subspecies than the common weasel. However, they seem to avoid warmer, drier, climes, and they are not found, for example, around the Mediterranean. They are, however, found in Ireland, apparently having got there under their own steam, which the common weasel failed to do.

The lifestyle of stoats is very similar to that of weasels, although they eat a slightly wider range of prey, including, for example, a much higher proportion of rabbits - the largest stoats can even take down a full-grown hare, an animal much larger than themselves. They store some of their food in chilly larders through the winter, but they will often switch to hunting different prey depending on what is available at certain times of the year, and have been reported to go as far as regularly dining on fruit when meat is in short supply.

Like common weasels, stoats from northern climes moult in the winter, producing a thick white coat. Unlike weasels, they keep the black patch on the end of their tails, and it has been suggested that this can serve to distract potential predators, who may end up directing their attention away from the stoat's main body. That common weasels don't do the same may be due to the fact that their tails are much shorter, making the tactic less useful. Unfortunately for the stoat, it is just large enough for this luxuriant white fur to be worth money, and thousands are killed for it every year. Indeed, the American name for the stoat, and, for that matter, that in almost every other European language besides English, is the same as the name for its winter pelt: ermine.

A stoat in winter

Not all stoats become white in winter, however. For example, those in England, where heavy snow is unusual and often short-lived, they rarely do so, while their neighbours in northern Scotland do so all the time, and those in between just develop some white patches. There's an obvious advantage to that, since being white makes you rather visible if it isn't snowing, but how do they manage it? It isn't just a genetic difference between the populations, because stoats taken from southern England and kept in the cold, do turn white - something they never do in the wild. On the other hand, there is apparently more to it than just temperature, since they regain their summer coats as the days lengthen, even if the room they are kept in remains cold. The details are unclear, although the moult appears to be under hormonal control.

Stoats and common weasels both vigorously defend their patch of land from same-sex members of their own species, although, even outside the breeding season, they aren't so bothered by the other sex, perhaps because males are much larger than females, and maybe aren't eating exactly the same food. They both prefer to mate in spring and summer, but the course of their pregnancies are quite different.

As one might expect for a small animal, common weasels have a short pregnancy, lasting only around five weeks, after which they give birth to a litter of around five young, initially weighing only one or two grams (about one twentieth of an ounce) each. The young are weaned within two months, and leave home within three, by which time they are almost fully grown. That's such a short time that the mother is capable of breeding again almost immediately afterward, and even the young can become parents themselves before the year is out.

Stoats, however, are quite different, and apparently better adapted for the prospect of a long winter. Although they mate at the same time of year, they don't give birth for another ten months, holding the embryo in suspended animation for all but the last month of that period - and thereby ensuring they will be born in the spring. Litters are about the same size, although the young are slightly larger, and covered with a short white fuzz, while newborn common weasels are hairless. The young take slightly longer to wean and leave home than those of weasels, but even so, some females can breed in their first year (although males, apparently, have to wait until the next one).

Even though stoats are hunted for their fur, neither they, nor the common weasels, are at all endangered, and their adaptability keeps both species numerous. They have even been introduced to New Zealand, where they now roam wild, as well as to some Mediterranean islands, and, in the case of the common weasel, to the Azores and the island of São Tomé off the west coast of Africa. Well adapted to farmland, and too small to be much of a menace to human livestock, common weasels and stoats have managed to do pretty well alongside humans.

[Pictures from Wikimedia Commons. Cladogram adapted from Koepfli et al. 2008]

Hanging Out with Other Species

2011-12-04T16:03:00.000Z

Spinner dolphin

Animals interact with members of other species in a range of different ways. Most obvious, perhaps, are predator-prey relationships, but not all interactions necessarily have to have the potential for violence. Often, we find members of different species living side by side because they simply happen to like the same habitat, or one species may steal the burrows of another rather than making the effort to dig their own. But there are also some more organised relationships, where two or more relatively large mammalian species actively congregate together for some sort of mutual benefit.

We commonly see this in herd animal, especially where one species is relatively rare within a given region. So long as they don't irritate the other species too much, it may be to the benefit of the rarer one to join the herd of the more common species, gaining the advantage from large herd sizes that it cannot achieve on its own. Aside from grazing herd animals, other social animals that often congregate with other, related, species, include examples among both primates and cetaceans. (Examples from other groups of mammal are rarer, but have been reported).

Broadly speaking, there are three different reasons why animals might want to actively hang out with members of another species. There is no particular why two or more of these reasons cannot be true at once, and disentangling them can take a fair amount of observation. Let's take a look at one recent study as an example.

Conducted by Jeremy Kiszka of the University of La Rochelle, and colleagues, this looked at two species of dolphin living off the coast of Mayotte, an island lying between Madagascar and Africa. The spinner dolphin (Stenella longirostris) and the pantropical spotted dolphin (Stenella attenuata) are somewhat similar in appearance, although the latter is noticeably larger, and they both live in warm waters across all three of the Atlantic, Pacific, and Indian Oceans. Both are also athletic and playful animals - the spinner dolphin, for instance, is not named after somebody Spinner, but because it likes to spin through the air as it leaps in and out of the water.

Spinner     Burrunan
Dolphin Dolphin   Common
   | | Bottlenose
   |           |      Dolphin     Clymene
   -------------       |      Dolphin, etc.
         |               |           ^
         |               |           |      Common
         -----------------           |     Dolphins
                   |                 |         ^
                   |                 |         |
                   -------------------         |       Spotted
                            |                  |       Dolphin
                            |                  |          |
                            --------------------          |
                                      |                   |
                                      |                   |
                                      ---------------------
                                                |
                                                |

As the above shows, despite the similarity in names, the two species do not seem to be that closely related. As I mentioned before, when discussing the newly "discovered" Burrunan dolphin, there is some degree of confusion as to how all these types of dolphin are related to each other, and the scientific names they are presently stuck with are not particularly useful. The spinner, spotted, and Clymene dolphins were all assumed to be related, on the not unreasonable grounds that they look much the same as one another, but it turns out that they are just as close to the bottlenose and common dolphins, which look quite different. This confusion has yet to be properly sorted out.

Over the years of their study, the researchers found that about one in five groups of dolphins actually contained at least one member of a different species, which is a relatively high proportion, in comparison with that found in other studies. In many respects, the associations seemed to be fairly random, although the mixed-species groups were larger than those with only one species, which suggests that just being able to get larger numbers together may be part of the animals' motivation. As with most dolphins, neither species is exactly numerous, with local populations of only a few hundred or so.

So, how do they benefit from these larger, mixed-species groups? The first of the three likely reasons is access to food. That is, either larger groups are better at finding food, or they are better at catching it (or both). This type of benefit has been observed, for example, in monkeys. However, it's pretty difficult to spot with dolphins, because they hunt their food underwater, where you can't see them.

Nonetheless, it does seem unlikely, for a couple of reasons. For one, the groups were spotted during the day, but both types of dolphin hunt at night, so they must have at least some other reason to stay together outside hunting hours. They also don't seem to hunt in the same way, which would make it difficult for them to cooperate. Specifically, spinner dolphins feed at greater depths - down to 400 metres - than spotted dolphins do, and may be eating different sorts of fish as a result.

A more likely explanation, perhaps, is protection from predators. Indeed, in general, this has been found to be the most common reason why different species congregate together. Diana monkeys and red colobus monkeys, for example, band together to ward off marauding chimps, while Thomson's and Grant's gazelles group up to protect against cheetahs. In the case of the two dolphin species, the main predators are likely to be sharks, although there are killer whales in the neighbourhood too.

The advantages of ganging up to form larger groups are two-fold when it comes to predators. The sheer size of the group may deter predators from attacking, and it's easier for members of the group to spot anything that's coming. Simply put, there is safety in numbers.

The researchers suggest a number of reasons why this is likely to be the main reason for the aggregations in this particular case. When they were spotted in mixed-species groups, the dolphins were usually travelling, rather than feeding or socialising and, in particular, the spinner dolphins were happier to travel out into deeper water when accompanied by spotted dolphins than they would be otherwise. That makes sense, because they're the smaller species, and potentially the more vulnerable to attack. Having larger dolphins around to help protect you may make you more willing to travel long distances.

There's also the factor that, while both species tend to hunt at night, the spinner dolphins are the more nocturnal of the two. Perhaps they are tired during the day, and less able to keep a look out for predators; if the spotted dolphins are more alert, that would clearly be a help for their sleepier cousins.

Finally, animals associating with another species might gain some sort of social advantage. For example, they might be able to defend a larger territory, thus gaining access to more food, without having to share with other animals that eat the same things as they do. This has been demonstrated, for example, with guenon monkeys. Or it could be something more nebulous, allowing social animals to hone their skills in the absence of many other members of their own species. Indeed, this has been shown with spotted dolphins before, albeit in this case, in groupings with bottlenose dolphins, where they have been observed to go as far as to engage in sexual activity and to look after sick bottlenose young.

In this particular case, there is no real evidence of that, but there isn't much evidence against the idea, either - especially if, for example, they were doing much of their interacting underwater where they weren't visible. Since there's no reason they can't do that and still help protect each from predators, it remains a possibility that there's something else going on that we can't see.

Sometimes, its not enough to understand how individuals interact with their own species. The world can be a little more complicated than that.

[Image from Wikimedia Commons. Cladogram adapted from Charlton-Robb, et al. 2011]

The Secret Life of the Monito del Monte

2011-11-26T14:34:00.000Z

There are something like a hundred species of marsupial in South America; hardly an insignificant amount. As I've mentioned before, the marsupials were, in fact, in South America before they ever reached Australia. While some headed south over the still green and verdant lands of Antarctica to reach the Australian continent beyond, others stayed behind, becoming the ancestors of the opossums and shrew-opossums that still live in the Americas today - including, of course, one species in the southern US.

But there is an oddity that confuses this simple picture, and that is a curious animal called the monito del monte (Dromiciops gliroides). In evolutionary terms, this gives every indication of being an Australian marsupial, being more closely related to animals like kangaroos than it is to American opossums. Which is a bit odd for an animal that lives in Chile and Argentina. How can this be so? The best guess is that the ancestors of Australian marsupials originated in South America before they crossed over to their new home, and that, for some reason, the monito del monte was the only one to survive in their original homeland. It is, however, also possible that the Australian marsupials really did originate in Australia - or, for that matter, in Antarctica - and that the monito del monte headed back to South America at a later date before the Straits of Magellan opened up.

Kangaroos,     Monito del     Bandicoots,
   etc.          Monte           etc.
^    |    ^
    |              |              |
    |              |              |         Shrew-
    ----------------              |        Opossums
           |                      |            ^
           |                      |            |        Opossums
           ------------------------            |            ^
                     |                         |            |
    "Australian" Marsupials              |            |
                     |                         |            |
                     ---------------------------            |
                                  |                         |
|     |
                                  ---------------------------
                                               |
                                               |

As you can see from the above, the shrew-opossums are also closer to kangaroos than they are to regular opossums. That, however, isn't an issue, because the Australian marsupials could easily have left for their continent after diverging from the shrew-opossums. The real problem is that the monito del monte is closer to kangaroos than bandicoots are, and the latter are uniequivocally Australian. Some analyses have even shown that the Australian carnivores (such as the Tasmanian devil) may have branched off before the monito del monte did.

Whichever way it happened, the monito del monte has been isolated from its Australian kin for many millions of years, and is, as a result, quite a unique little animal. It is not just the only member of its family, but the only member of its order - a higher level grouping, intended to be on a par with, for example, "primates" or "rodents". Yet, because it's relatively rare, is nocturnal, and lives only in remote forests in the Andes mountains, we don't know all that much about it.

The animals are moderately sized - about a foot long - and apparently spend most of their lives in the trees, preferring southern beech forests, stands of bamboo, and anywhere with plenty of vines and other tree-creepers. They're quite picky about their habitat, which is a problem, considering the advance of agriculture in the area. They are considered "near-threatened", which is to say that they may not be in danger yet, but that could easily change. However, given how little they've been studied, it's not easy to know how well they're really doing.

One of the first studies of population trends in this species was recently published by Marcela Franco, of the Southern University of Chile, and co-workers, who also took the opportunity to examine several other features of the animal's lifestyle.

Over four years, they found a total of 163 individuals in a 60 hectare (150 acre) patch of woodland north of Valdivia, in Chile. That's rather more than previous studies suggested would be found in such a small area, which suggests either that they were better at finding the animals (which is perfectly possible, given the limited number of prior studies), or perhaps that the animals were becoming crowded into relatively small forests as the growth of agricultural land prevented them from leaving. At least as importantly, there was no real change in the population over the four year period of the study, which at least suggests that the animals are holding on reasonably well.

By examining and weighing the animals, they found that, while females are generally bigger than males anyway, they particularly put on weight towards the end of summer. This makes sense, given that the monito del monte hibernates when the weather gets cold (indeed, the scientific name "gliroides" means "like a dormouse"), so animals will want to put on weight as the summer draws to a close, to prepare for the long winter snooze. This was, as expected, most notable around the tail, where these animals seem to store most of their fat reserves, using it rather like a camel's hump.

In addition to confirming that the animals are nocturnal, being active mostly between midnight and dawn, they also looked into how they sleep. It had previously been reported that the animals huddle together in spherical nests during the day, and one possible explanation for this would be to keep each other warm. Small animals lose heat more readily than larger ones, so it would not be surprising if the monito del monte, an animal that we know doesn't like the cold, would be among the many that do this.

But, apparently that's not the reason. Because the study showed that the animals were less likely to sleep together during the winter, and, even when they did, the huddles were, on average, smaller. If you cuddle up mainly to keep warm, it would make no sense to do it mostly during the summer, and hardly at all when the weather was at its coldest. Instead, they are huddling together the most during and immediately after the breeding season, which suggests its more a matter of looking after young, and of being relatively social animals that prefer to stay with their relatives, something that's presumably less important in winter when they're all asleep anyway.

All of this is important if we want to prevent the monito del monte from becoming endangered - something that it has, so far, avoided. Understanding when animals are active helps us know what other animals might eat them, and their social behaviour, habitat preferences, and typical population densities are all important to working out how they will fare as their forest environment becomes more fragmented. As with so many animals, it's not just their own well-being that's at stake; they play an important role in the ecology of their local habitat. For example, they are only known animal to spread the seeds of a local form of mistletoe that is, itself, a key part of the overall health of these particular forests.

And a little more light has been shed on a rather curious corner of the world of mammals.

[Picture by Jose Luis Bartheld, from Wikimedia Commons. Cladogram adapted from Asher et al. 2004]

News in Brief #2

2011-11-24T21:19:00.000Z

Columbian ground squirrel

The Wooing Ways of Ground Squirrels

Male animals will go a long way to ensure that they become the father for a female's young. If the female isn't likely to be monogamous, they may chase off rivals, beat them up, display their masculinity, or just have giant gonads. But male Columbian ground squirrels (Urocitellus columbianus), it seems, like to try a bit of smooching.

Columbian ground squirrels (that's British Columbia, by the way, not Colombia in South America) live in complex, underground burrows. They mate in the early spring, after waking up from hibernation, and the females are sexually fertile for just one day during each year, making competition between males particularly important. Yes, the males do fight one another to establish territories, but, according to a new discovery, that isn't their only trick.

In short, they don't go too far on a first date. They sneak into the female's burrows at night, when she isn't sexually fertile, and spend the night with her, without doing anything. The next morning - and the more experienced males do seem to be pretty good at predicting in advance the one day when this is going to happen - the females wakes up feeling randy... and, well, who's already there?

Admittedly, that isn't an end to the matter, since the females will be at it for up to another seven hours, with as many males as can get close to them, but being first makes all the difference. The males who successfully work out who they should be waking up with in the morning father the most children. Generally, that's the older ones; younger males are either more impatient, or just get little opportunity to kip in someone else's burrow, so, while they'll get their chance later in the day, by then, they've already missed their best chance.

Getting in Deep Water

When we see images of seals, they are usually lounging about on the coast. That's by and large because they're there to breed and raise their young, before they get old enough to fend for themselves. But, of course, seals spend most of their year out at sea where they're much harder to spot. Young seals, in particular, must face a challenging time when they first head out into deep waters. They have only just learned to survive away from land, and we might expect that, at first, they have to get used to the idea, and are less adventurous than their older relatives.

A recent study looked at the diving behaviour of southern elephant seals (Mirounga leonina) to see what differences there were between younger and older individuals. They tracked the seals off the coast of Argentina, where there is an exceptionally wide expanse of continental shelf. That means that the seas are relatively shallow, with plenty of plants for fish to eat, and therefore plenty of fish for the seals to eat. They were particularly interested in how much effort the seals put into diving, using light loggers attached to the animals to see how long they spent below the surface (a pressure gauge of some kind would have been better, but much more expensive).

The young animals (that is, less than three years old) turned out to be less willing to take long and deep dives and less willing to leave the shallower seas, compared with the older ones. Although its plausible that they weren't fit or experienced enough to make the really deep dives, we do know that they could travel into deeper waters if they felt like it, because some did - just not very often. Indeed, a few travelled thousands of kilometres out to sea, in some cases rounding the Cape Horn and heading out into the Pacific. That they didn't all take the easy option suggests that some were pushed out by their relatives and had to venture far afield. That most didn't may explain why this is a good area for elephant seal breeding - the adults may not care whether water is shallow or deep, but it's a big help for those that are still growing.

Synchronising Sex, not Cycles

Columbian ground squirrels may be able to predict when females are going to come into heat, but, as we've seen before, male Assamese macaques aren't so lucky. Now a further study by the same researchers has looked into exactly when mating occurs in this species. In many mammals, there can be an advantage to synchronising ovarian cycles. The argument goes that, if all females are receptive at the same time, one male can't monopolise them all, and the female gets her choice of preferred partner.

Although there is some debate on the matter, it's generally thought that primates don't, as a rule, synchronise their ovarian cycles. That may be because, compared with other mammals, they tend to be fairly promiscuous, so that a small number of males monopolising all the females is inevitably quite difficult (monogamy, is of course, an alternative tactic). This new study showed that, as judged by hormone levels, female Assamese macaques were no exception - they do not synchronise their fertile cycles with other members of their troop. Which goes some way to explaining why the males can't figure out when they are.

However, it turns out, that while they may not synchronise their biological cycles, the female monkeys do synchronise their sexual activity - that is, they all tend to mate on the same days. Why so? We don't know, but the authors suggest that it may have a lot to do with the unusual mating habits of the Assamese macaques. Females, you may recall, tend to prefer particular males, and they don't really care if he's the dominant one, so long as he helps care for them and their offspring. The dominant males, though, being dominant, do want to mate with as many females as possible - but they can't do that if they're busy elsewhere. If so, this must be a behavioural tactic by the females, not just the result of their hormonal status, because we already know that they're just as likely to mate whether or not they are currently fertile.

Winter Wolves

There have been many studies looking at the hunting strategies of wolves, and how they travel long distances in search of prey, roaming over large expanses of the countryside, especially in the barren north. But, if you go far enough north, then, at certain times of the year, the sun never rises. We have, perhaps unsurprisingly, no studies on how the wolves of the far north behave during these weeks or months of perpetual darkness. Until now, that is. Researchers radio-tagged the leader of a wolf pack living on Ellesmere Island, to determine whether or not they behaved differently during four months of total darkness and temperatures down to -53°c.

Apparently, they don't.

New Fossils Reported

From the middle Miocene of Patagonia comes a report of a new species of rodent, Microcardiodon williensis. This is a relative of the guinea pig family, although slightly too primitive to belong to that family itself. The fossil consists only of half of the lower jaw, and is about 5 centimetres long. Even so, it is significant because one of the defining features of the guinea pig family concerns the shape of the jaw, and, especially, the teeth, and because the fossil comes from a time period when prehistoric guinea pig-like animals were just giving way to the first members of the modern family. This animal showed one of the three key features that distinguish true guinea pigs from those earlier fossil forms. We already have one, slightly later, fossil of an animal with two out of the three features - and plenty of earlier ones that have none - so this shows, not only a key point in the evolution of guinea pigs (and especially the adaptation of their teeth to the tougher plants that were becoming more common at that time), but shows that that evolution was a gradual, stepwise one, not a sudden burst as had previously appeared to be the case.

From just a tiny bit later, and from the same continent - although in this case, rather further north, in Bolivia - comes another jawbone. This one belongs to a sloth, Hiskatherium saintandrei, but quite how it relates to other sloths isn't clear. It is related, in some way, to the giant ground sloths, such as Megatherium, but this animal was much smaller, perhaps even smaller than sloths are today. Beyond that, all we can say is that it doesn't seem closely related to anything, although the jaws of sloths are sufficiently strange that that may be more of a limitation of our understanding than because this sloth is a genuine oddity. Interestingly, one thing we can say is that the animal apparently had an unusually long snout, and presumably a long tongue, perhaps for grabbing onto foliage.

A jawbone may not sound like much to form the basis of a description of a new animal, but our final fossil is just a single tooth. It is, apparently, the last upper premolar, and is about 5 millimetres across, so it didn't exactly belong to anything huge. It may not tell us much about the form of the animal that left it, but that doesn't mean it tells us nothing at all. For one thing, its similar, but not quite the same, as one we've seen before, so that we can say it belongs to a newly discovered species of the primitive omnivorous mammal Protungulatum. This, in turn, belongs to a group of animals that were amongst the most dominant of the Paleocene, the earliest epoch of the Age of Mammals, when they first spread across the globe in the wake of the devastation that wrought the death of the dinosaurs.

Except that this fossil is not from the Paleocene, but from the Cretaceous. It is, apparently, the first time we have found a fossil of such an animal that dates to before the K/T extinction, when dinosaurs still walked the earth. It certainly belongs to the line that led to the placental mammals, and was itself, most likely, an actual placental, although primitive enough that that's hard to know for certain. But, if it is, it may well be the oldest placental fossil ever discovered. Not a bad find, from one tooth.

[Picture from Wikimedia Commons]

When Whales Walked the Land

2011-11-20T13:48:00.000Z

Protocetus, a close relative of the new species

The Eocene, the second epoch of the Age of Mammals, was a time of many strange creatures. The mammals were well established by this point, but few of the modern groups of mammal we are familiar with had yet evolved, and those that had did not necessarily look the same as they do today. Take the whales, for example:

Today, there are two basic types of whale. The odontocetes, or toothed whales, are the largest group, and include the porpoises and dolphins, as well as several larger species, including the mighty sperm whale. The other group are the mysticetes, or baleen whales, which have no teeth, and are instead filter feeders. This latter group includes the right whales and, perhaps most famously, the blue whale, which, so far as we know, is the largest animal ever to have lived.

Both of these groups first appeared at the end of the Eocene, but in those days, they shared the seas with a third, older, type of whale, that would die out during the following, Oligocene, epoch. These were the archaeocetes, and they include the original whales from which all the others later evolved.

Like most mammals, the archaeocetes did, of course, have teeth. But their teeth were very different from those found in living toothed whales. One of the distinctive features of mammals, compared with most reptiles, is that they are heterodont, that is to say, that they have more than one kind of tooth in their jaws. They have cutting incisors at the front of the mouth, followed by stabbing canines, and then grinding premolars and molars for chewing up food. Of course, not all mammals have all four kinds of teeth - herbivores, in particular, have often lost the canines over the course of their evolution - but the general principle remains the same.

But toothed whales, dining as they do, on fish and soft-bodied squid, are unusual (though not unique) among mammals in having lost this pattern altogether. The teeth of whales and dolphins are usually all the same, simple, conical shape, and, in the few exceptions, they're so peculiar and highly specialised that they can't possibly be fitted into the usual categories of incisors, canines, and cheek teeth. But this wasn't the case among the archaeocetes.

That alone would have made the archaeocetes look quite different to modern whales. When they opened their mouths, they would have revealed teeth looking more like those of a land mammal than those we are used to in, for example dolphins - perhaps more like the teeth of a long-snouted dog than anything else. Nor is this the only way in they were different from the whales that followed, as is illustrated by a new fossil reported earlier this month by Giovanni Bianucci and Philip Gingerich.

This was not the result of any fossil-hunting expedition. Instead, it was found in a block of marble dug out of a stone quarry in Egypt. When the stone arrived in Italy, the architects who had planned to use it discovered the presence of the fossil, which, being made of a softer material than the surrounding stone, made it useless for its intended purpose. Fortunately for science, rather than throwing it away, they donated it to the University of Pisa.

The fossil turned out to consist of the head, backbone and ribs of a previously unknown species of whale, now officially named as Aegyptocetus tarfa, after its place of origin. From the geology at the quarry, they determined that it lived around 40 million years ago, towards the end of the Eocene. When it was alive, it would have swum in the shallow waters of the Tethys Sea, a broad body of water that, in those days, separated Africa and India in the south from Europe and Asia in the north - parts of it remain today as the Mediterranean Sea and Persian Gulf.

The skull measures about 68 cm long, which probably means that the living animal would have been very small by modern standards - much smaller than, say, a killer whale, although still considerably larger than a typical dolphin. It had a full complement of teeth, and, together with other features, this enabled the researchers to identify it not only as an archaeocete, but as a relative of another Egyptian fossil, Protocetus. In the paper, they make much of the unusual sloping shape of its head, something that sets it apart from its relatives, although they concede that they have no idea what the significance of this might be.

The skull has a slight asymmetry, a feature seen much more strongly in living whales, and the result of the movement of the nostrils up onto the forehead to form a "blow-hole". The placement of nostrils further back on the head is a common feature of aquatic mammals and reptiles, presumably making it easier for them to breathe while swimming. Seals, for example, may not have a blow-hole, but they do have nostrils placed much further back than those of a dog or horse, and this animal was probably much the same.

The way that the original block of marble had been cut into slabs also meant that it was possible to see cross-sections of the nasal cavities, and these turned out to contain large sinuses and well-formed turbinate bones. These latter bones form baffles within the nasal cavity that are covered with cells responsible for our sense of smell, which this animal presumably had to a fairly high degree. That's significant, because living whales are quite different, having little, if any sense of smell, since, being below water for so much of the time, they have no use for one.

Furthermore, the backbone has strong spines that, in life, would have anchored some of the muscles mammals use when walking. Although its legs weren't preserved, this implies that the animal was, at the very least, capable of moving about on land, and perhaps finding food there. On the other hand, the structure of its ears suggests that it would have been far better at hearing underwater than it would have been in air.

Taking this mixture of features together - smell adapted for land, hearing adapted for water, and so on - we can say that, unlike any living whale, Aegyptocetus was only semi-aquatic. Although there's no way to know for sure, it may have lived somewhat like a seal, able to move about on land, but doing much of its hunting in the sea.

We know that it died at sea, because of some other interesting features of the skeleton. There are bite marks on some of the ribs, matching the teeth of a shark, so the animal was clearly attacked at some point. The attack may not have been fatal, and the fact that the ribs are still there certainly suggests that the shark can't have eaten too much of it even if it was, but it does tell us something of the animal's life. More significantly, perhaps, the skeleton shows marks from barnacles that must have encrusted it after it settled to the bottom - a clear indicator it was underwater at the time. The barnacles are mostly found on one side of the skeleton, so we can even tell which way up the body was lying in the soft sediment of the sea floor.

Aegyptocetus lived too late to be the direct ancestor of modern whales, but its existence shows that, even as its cousins were just beginning to take to the sea full-time, some whales continued to live along the boundary, taking the best from both the dry and wet worlds.

[Image from Wikimedia Commons]

Weasels on the Riverbank: Mink

2011-11-13T12:04:00.000Z

European mink

While most are still terrestrial, the long sinuous bodies of weasels are easily adapted to an aquatic lifestyle. Within the lineage that led to the modern weasels and their relatives, semi-aquatic habits have evolved at least three times. The first of those lines led to the otters, but the most recent led instead to the European mink (Mustela lutreola), a much smaller animal that is clearly not an otter, and is, in fact, most closely related to the ferrets and polecats.

The European mink was once found throughout central and eastern Europe, from Germany in the west to European Russia in the east. It is almost as aquatic as an otter, and is never found far from fresh water, preferring dense vegetation along the banks of fast-flowing streams and small rivers. Its feet are partially webbed, and it is a good swimmer in comparison to most other members of its family, although not as skilful as the otters. Mink den in natural hollows, such as those beneath tree roots, and will also take over the burrows of their favourite food, water voles.

Even so, while they are undeniably well adapted to a semi-aquatic lifestyle, they are no match for otters. For example, mink do not see well underwater, and only dive after fish, crayfish, and so on, after they have spotted them from above the surface. Given that otters and mink both inhabit the same parts of Europe, why aren't the latter simply out-competed? It turns out that it's their very lack of adaptation that helps them survive.

Otters are superbly well adapted to the riverine life, and if both animals compete only to catch fish, the otter is going to win hands down. Which is good news for the otter when there are lots of fish about. But when there aren't, for whatever reason, mink can easily switch to catching prey on land, eating voles, small lizards, and birds. True, they rarely travel more than a hundred metres or so from the riverbank, but that's generally further than otters are happy going, and the mink can readily live on the boundary, taking food from both water and dry land, allowing them to live alongside both the otters and their more terrestrial relatives, such as polecats.

Like most members of the weasel family, mink are solitary animals, with each individual staking out a claim to a stretch of river anything from a few hundred metres long to a mile or more. Although there is some overlap between the territories of different sexes, they meet up mainly to mate, when the male may travel long distances in an effort to mate with as many females as he can find. Indeed, this seems to be the main way that the male shows his physical prowess. Females don't seem to care who they mate with, and will happily do so as many times during the breeding season as they can, so, to start with, everyone gets a look in. But the males' journeys are long and exhausting, so that, as the season draws to a close, only the most physically fit are still at it - and it's whoever the female mates with last that gets to father her young.

Females also seem able to control exactly when they give birth. It takes around five weeks for the young to develop, but the female is able to delay the start of that development for up to another five weeks, keeping the embryonic ball of cells inactive in her womb until she senses that it would be a good time to start the pregnancy proper. As a result, pregnancy can last anything up to ten weeks, before a litter of about four to six young are born in April or May. Like many mammalian carnivores, the young are born blind, and, in mink, they don't open their eyes for four or five weeks. They leave home in the Autumn, establish their own territories along the riverbank, and are ready to reproduce by the time the next mating season rolls around in February.

When European colonists first arrived in the North America, they encountered an animal that looked remarkably similar to the one they were already familiar with, and, unsurprisingly, they also called the new animal a "mink". Indeed, so similar were the two species that, for a long time, it was assumed that they were close relatives, perhaps only diverging from one another when the Bering Straits formed at the end of the last Ice Age. However, modern genetic studies have shown that that this isn't the case.

It turns out that the American mink (Neovison vison) represents a third semi-aquatic lineage within the family, diverging from the other weasels long after the otters did, but also long before the European mink. Indeed, the two species last had a common ancestor, not a few thousand years ago, but five million, long before even the first Ice Age. That they look so similar is due, not to a close relationship, but to parallel evolution, where both animals have adopted essentially the same lifestyle.

The American mink is slightly larger than its European namesake, and the white markings on the chin usually (although not always) do not extend to the upper lip as they do in the other species; other than that, they really are quite hard to tell apart. The American species does seem the more adaptable of the two, and it is more ready to live on lake-shores or in marshland, as well as along rivers. This has allowed it to spread across the North American continent, from Florida and the Mississippi delta as far as central Canada and Alaska; aside from some islands and the high Arctic, about the only place it isn't found is in the southern deserts.

Like the European species, American mink often take over the burrows of their favourite prey animal - in this case, the muskrat - but they are also much more willing to dig burrows of their own. Females, in particular, can dig tunnels up to three metres long, with nests at the end in which to raise their young. In many other respects, the two species are near-identical. They have similar habits and swimming abilities, eat more or less the same kinds of food, and have similar breeding patterns and lifespans. However, there is another factor that has led to a dramatic difference between the fates of the two species.

Like many other members of the weasel family, the European mink had long been hunted for its fur. The American mink, however, turned out to have even more luxuriant and valuable fur, which made it a favourite target for trappers - it is this animal that is currently used to make mink coats. As it turned out, the American mink was widespread enough and common enough that this was never a threat to its continued survival, and, today, only one of the fifteen subspecies - that in southern Florida - is considered endangered. Indeed, wild trapping began to decline in the nineteenth century, as, from 1866 onwards, fur farms were established to raise large numbers of the animals in captivity.

Although never as domesticated as the ferret, farmed American mink have nonetheless been bred to develop fur in a range of different colours, from pure white, through tan, brown, and grey-blue, to near-black. So successful were these fur farms that new ones were established outside America, and, starting in the early twentieth century, farmed mink were introduced to Europe, and, much more recently, also to China and Japan. The problem was, the mink proved pretty difficult to keep penned up, and, from at least the 1920s, they began to escape into the wild.


American mink

Being adaptable animals, the newly escaped mink soon found new habitats to colonise, and they were happy to feed off prey such as water voles instead of muskrats. In places such as Britain, that had never had European mink, this wasn't much of a problem, and American mink are now found across Britain, Ireland, Scandinavia, parts of Italy, and even Iceland. But, where the European mink already existed, it was not the same story.

European mink were able to survive alongside otters because of their more generalist lifestyle, but against the very similar American mink, it was another matter entirely. Larger, and perhaps slightly more adaptable, the American mink began to out-compete the natives, and they went extinct across much of their range - the mink now found in places such as Germany and Poland are all the American species, not the native one. The majority of European mink alive today are found in Russia, and even there, they occupy only a few fragmented areas, and their population seems to be declining. There are also a few in Latvia, Estonia, Belarus, and around the Danube delta in Romania. From the 1950s, a few even fled westward, and colonised parts of France and Spain, where they had previously been unknown, but even these populations have not thrived.

The European mink was already in trouble before its American namesake arrived, largely due to destruction of its native habitat by increased agriculture, and, in more recent times, river pollution has certainly not helped. The species is now considered critically endangered, with less than 25,000 left in the wild, and those numbers declining rapidly. There have been attempts at conservation, including some introductions to isolated islands, and even implanting embryos into polecat/mink hybrids, but, so far, the animal remains in danger of extinction. Still, it could have been even worse.

The sea mink (Neovison macrodon) once lived along the rocky shores of eastern North America, from Newfoundland down to Massachusetts, where it apparently fed on fish, and possibly also on shellfish and other animals. It was much larger than either of the other two species of mink, at over 60 cm (not counting the tail), closer in size to an otter than to the 35 cm of a typical American mink. It's fur was more reddish in colour than that of its neighbouring species, and that larger size made it's pelt even more valuable. We don't know exactly when fur hunters finally killed the last of the sea mink, although it was probably some time around 1860. More recent sightings, as late as the 1890s, were probably mis-identifications of American mink, which subsequently inhabited the same area.

Either way, while animals such as the black-footed ferret have come perilously close, the sea mink remains the only member of the weasel family to have gone extinct in recent historical times, and it was not even scientifically described until 1903, long after it had vanished. Conservationists may be struggling to save the European mink, but all of that has come far too late for the sea mink, an animal now entirely consigned to the history books.

[Pictures from Wikimedia Commons. Cladogram adapted from Koepfli et al. 2008.]

Why Marsupials Can't Fly

2011-11-06T12:20:00.000Z

A sugar glider is as close as it gets...

One of the significant features in the early evolution of mammals was the development of a different posture from their ancestors. Living reptiles, such as lizards and crocodiles, have a sprawling gait, with the limbs splayed out to the side, but, in almost all mammals, the limbs are held erect, directly underneath the body. This has a number of advantages. For example, the body no longer has to bend from side to side as the legs move, which allows the lungs to operate more efficiently - you aren't constantly having to squeeze one of them at a time as your chest flexes. Having the shoulder blades placed more vertically also allows them to have more of a direct involvement in limb movement, effectively giving an extra segment to the limb.

This feature is not unique to mammals, because it also evolved in dinosaurs, and in some prehistoric crocodiles - which, rather alarmingly, could run rapidly across dry land. Today, of course, it is also found in birds. Nonetheless, it is a key feature of mammals, and the starting point for a whole series of adaptations in mammalian limb structure. From this beginning, mammalian limbs have taken on a wide range of different forms, adapted to all kinds of different lifestyles.

One example would be the development of hooves. The stance of hoofed animals, standing on the very tips of their toes, is thought to give the limb greater flexibility and allow them to run faster. Hooves have therefore evolved in herbivores, to, at least in part, allow them to escape from predators. Given the speed at which, for example, a cheetah moves, hooves clearly aren't essential for rapid running, but they do seem to help, and one might wonder why predators - as keen to catch prey as the prey is not to be caught - never evolved them. The answer, most likely, is that claws are just too useful to carnivores, which use them as weapons to bring down their prey; something that wouldn't work with a hoof.
With the great variation of mammals that exist, its quite obvious that the proportions and shapes of limbs vary considerably between them. Still, there are some limits to this variation if you want to be able to walk or run effectively, and a couple of years ago, Manuela Schmidt and Martin Fischer of Jena University conducted a study comparing the limbs of a wide range of mammalian species to look at those limitations. One of their conclusions was that the hind limbs of mammals vary far less than the fore limbs.

This, they suggest, is because the hind limbs are the main source of propulsion, important for pushing off from the ground as the animal walks or runs. Fore limbs, on the other hand, can be modified for a range of different functions, such as digging, grasping objects, and so on. In some mammals, such as humans, the fore limbs aren't used for walking at all (at least after the first year), but they still need the hind limbs to do that. Bats are another extreme example, with their arms turned into wings, but still needing their hind limbs as... well, legs.

No great surprise there, then; front limbs vary more among mammals than hind limbs do. Sure, hind limbs do vary - consider rabbits, gazelles, badgers, and monkeys, for example - but not as much as the fore limbs. But it seems that the story may not be quite the same when it comes to marsupials.

Now, marsupials only represent around 6% of mammal species, but they have had a whole continent to themselves (not to mention sharing the Americas), and have evolved to fit a wide range of lifestyles and habitats within it. Many of them closely resemble placentals in similar environments. Even the most distinctive marsupials, the kangaroos, aren't a million miles away from a rabbit in shape, if not in size. But there are some body forms they just haven't evolved.

For one thing, there are no marsupial dolphins, which rules out what are arguably the most extreme limb adaptations of any mammals. Given that the pouch would fill with water, that's scarcely surprising. Indeed, while there are some semi-aquatic marsupials, water in general is something they've not been too effective at exploiting. But it's more than just that; there are no marsupial antelope, either, or bats. Some marsupials can glide, but all of the flying mammals in Australia are placental bats that made the trip across from south-east Asia. Did they just never get the chance to evolve wings, or is there more to it than that?

Kelly McKenna and Karen Sears of the University of Illinois thought that there might be, so they conducted a new survey of limb shapes among mammals. Like the German study, they examined the variation in the width and length of the various segments of the limbs - shoulders/hips, upper limbs, and lower limbs - but, this time, they specifically compared marsupials to placental mammals. Their first finding was that placental limbs are, indeed, more variable than those of marsupials. Given that they were including dolphins, seals, and bats in the survey, that's not exactly surprising news.

What's more interesting is that they also compared marsupials and placentals that shared a similar method of locomotion. Animals that walk on all fours through the trees, for example, such as squirrels and possums, might be expected to be fairly similar between the two groups. Yet even here, in most cases, the marsupials varied less than the mammals. The one exception was when it came to animals that hop along on their hind legs, where kangaroos and wallabies do vary more than, say, rabbits and jumping mice. But even then, while the placentals they looked at did not vary very much, they were more specialised. That is, while their limb shapes were all pretty much the same, they were less like those of the "average" mammal than those of kangaroos and wallabies.

More than that, it seemed that when marsupials did have more specialised limbs, they were more likely to be the hind limbs than the front ones. Again, think of kangaroos. That's the opposite of what happens in other mammals, and it didn't show up in the German study for the simple reason that the great majority of mammals aren't marsupials. It's not just that marsupials never have wings, in general, their fore limbs are less varied than those of placentals... but, if their fore limbs are just as free from the need to be the main source of propulsion as they are in placentals, why is that?

The answer, as one might expect, is almost certainly to do with reproduction. A marsupial is born as a tiny, undeveloped baby, little more than an embryo, and must crawl through its mother's fur to reach the pouch (or at least, the teats) where it can finish its development. To do that, it uses its front limbs to pull itself along, so it is they, at this crucial stage of life, that are the important ones. That means that the baby has to be born with front limbs in, more or less, the same shape, which limits what the can eventually change into as it grows. That is why marsupials never have wings; it would be harder for a winged infant to crawl into the pouch than for one with grasping claws. Hooves, presumably, would be even worse.

It surely wouldn't be easy to fly about with a baby in your pouch, but if a winged marsupial couldn't even be born in the first place, you'd never get the chance to try.

[Picture from Wikimedia Commons]

On the Origin of Tigers

2011-10-30T13:20:00.001Z

South China tiger, perhaps the most primitive living subspecies

The tiger (Panthera tigris) is surely one of the most iconic of all mammals; instantly recognisable, and widely used in images illustrating the beauty of the world's wild animals. But what is the history of this most familiar of beasts? How did the tiger come to be?

There are six living subspecies of tiger, and at least a further two that went extinct as recently as the twentieth century. One way to trace the origin of tigers is to examine the genetics and physical features of the different subspecies and see how they compare. When we do this, we find that the Sumatran tiger appears to be a distinct lineage (it has even been suggested that it should be a considered a separate species, although nothing has really come of this), although the critically endangered South China tiger may have arisen even earlier. One of the first splits after this involved some tigers heading out to the eastern parts of Indonesia, where they established themselves as the Javan and Balinese subspecies - both now extinct. Of those on the mainland, one headed to India as the Bengal tiger, while the other went further north to become the Siberian tiger. The remaining two subspecies, the Malayan and Indochinese, are clearly related to one another, although there is some dispute as to whether they are closer to their relatives in Siberia or those in Bengal.

But when did all this happen? Genetically speaking, all of the subspecies are remarkably similar, and, using estimates for how fast genetic changes accumulate among cats, it is generally agreed that they first diverged less than 100,000 years ago, and perhaps as recently as 76,000 BC. That may sound like a long time ago, and it's during the earlier part of the last Ice Age, which makes sense given the great changes in climate and vegetation going on at the time. But, compared with the other big cats, its actually fairly recent. We know, just from fossils, that the various living forms of big cat must have originated well over a million years ago, which leaves plenty of scope to discover more about the earliest history of tigers, and how they came to be different from lions, leopards, and jaguars.

The oldest fossils of the pantherine subfamily (that is, lions, leopards, jaguars, and tigers, as opposed to, say, cougars, cheetahs, or sabretooths) come from Tanzania, and date to over three million years ago. They are, however, fairly fragmentary, consisting of a few pieces of the jaws, and some scattered bones from elsewhere in the skeleton. The animal that left them was probably either a lion, a leopard, or something closely related to both species, but the details are rather unclear. From more recent deposits, we know of the American lion, which is probably a distinct species from its Old World cousin, the European cave lion, which may or may not be, and the European jaguar, which is certainly not the same thing as its South American counterpart. It has generally been believed that the closest extinct relative of the tiger was Panthera palaeosinensis, which lived in China some time around two million years ago.

However, that's beginning to look rather shaky. Just last year, a study was published that seemed to indicate that this fossil was closer to a lion or leopard than it was to a tiger. Now, however, the same author has published a fossil discovery that may well tell us a lot more about the origin of tigers. In a recent paper, Ji Mazák of the Shanghai Science and Technology Museum, together with European colleagues, describe the discovery of the oldest complete pantherine skull so far found - and it turns out to resemble a tiger.

It was discovered near Dongxiang in Gansu, China, and has been dated to somewhere between two and two-and-a-half million years ago. That places it, not during the last Ice Age, but during the first one (or, at least, the first during the Age of Mammals). Named as the "Longdan tiger" (Panthera zdanskyi), the fossil consists of a remarkably intact skull, complete with the lower jaw.

The skull is small, compared with those of living tigers, suggesting that the animal was about the size of a jaguar. However, the canine teeth are exceptionally large, and the nasal bones long, both features seen in tigers, but unusual or unheard of in other big cats. The general shape of the skull is about mid-way between that of tigers and jaguars, and, while it seems to me that the authors are perhaps, over-egging the resemblance to tigers in this respect, the tiger-like teeth do seem to support the contention that this isn't a jaguar.

It is, however, the lower jaw that most strongly indicates that the specimen belongs to a new species, rather than being some previously unknown jaguar-like subspecies of tiger. This jaw is different from that of any living species, and quite dramatically different from that of a jaguar. Instead, its shape is part way between that of a tiger and that of what is, perhaps, the least well known of the living big cats, the clouded leopard of South East Asia. The clouded leopard is often considered the most "primitive" of the big cats - which is to say, it has changed the least since the time of their last common ancestor - so this would make sense, given the age of the fossil. Indeed, in this respect, the fossil resembles those of other extinct cats, most notably American lions.

Tiger    "Longdan Tiger" Leopard    Lion
| | | |
| | | |     American
| | | | Lion
--------------- -----------    |
   | | |
   | | | Jaguar
   | ---------------    |
   |    |     |
   |    |     |
   |    -------------------
   | |
   | |
   -------------------------------------------
|
|

This, at least, is the relationship favoured by the authors in this paper, based on earlier work by Christiansen et al that used skull and tooth shape as its basis - somewhat essential, if you want to include long extinct fossil species in your analysis. Other studies, using genetics, have placed lions and tigers much closer to one another, but, for obvious reasons, have not included anything you can't get a blood sample from.

The authors speculate that their animal may represent the actual ancestor of living tigers, although there can be no way to know that for certain. Despite the skeletal resemblances, the illustration in the paper of what the authors think the animal would have looked like when it was alive (which you can see here) shows clear differences with the modern tiger, even allowing for the fact that they haven't chosen to give it stripes. Nonetheless, it seems to be a close relative, and it lived long before the modern tiger diversified into its various subspecies.

Whatever else it may be, the animal was about the size of the very smallest adult female tigers alive today, although it was apparently a male, which means it should have been much bigger. Whether or not it is the direct ancestor of modern tigers, and whether, therefore, tigers first appeared in northern China before spreading south to India and Indonesia, its clear that one of the main things that happened to their lineage is that they gradually increased in size, and presumably did so over the course of the Ice Ages. Perhaps tigers needed to become larger, because their prey was doing the same. Deer and bovines, which are among their favourite prey, were both growing over this time frame, and it may be that as their prey became larger, so the tigers also grew to make it easier to take them down.

[Picture from Wikimedia Commons. Cladogram adapted from Mazak et al, 2011]

The Mother Elk's Dilemma

2011-10-23T13:53:00.000+01:00

A male elk

Giving birth and looking after newborn young are particularly dangerous times for the large hoofed herbivores. That isn't to say that it isn't difficult for other mammals, too, or, indeed, other animals in general, but the larger herbivores are especially vulnerable. Smaller animals can hide their young in burrows, or other secluded dens, until they come of age, while the larger carnivores don't generally have to fear being eaten. Large herbivores do not have such a luxury.

However, hiding from predators while the young are still small and vulnerable is not the only concern that mothers have to face. Giving birth is costly in terms of resources, and after that, the young must be fed milk until it is large enough to search for food on its own. The mother, therefore, needs to keep herself well fed, and needs a good supply of food to keep both herself and her infant healthy. While this is obviously true at any time of the year, during the birthing season it becomes particularly important for the mother to find an area that is both free of predators, and has a ready source of available food.

That can be a problem if the areas that have the best food are also the ones that have the most predators.

Which is a common situation; if nothing else, predators do tend to congregate where their prey prefer to live. So how does a mother resolve this problem? Clearly, she will have to accept some sort of trade off, depending on whether she is more worried about her child starving to death or being eaten. Exactly how she will do that depends on the exact environment and the nature of any challenges that the animal will face.

The way that animals approach this dilemma has been studied in a range of different animals, including antelope, moose, reindeer, and goats, among others. Spencer Rearden and colleagues, of Oregon State University, have recently extended this to study elk living in the Blue Mountains of their state. Before I look at that, though, I should explain that there is considerable confusion as to what exactly an "elk" is.

Firstly, there's the common name. In Europe, the word "elk" refers to the animal Americans know as a moose, and that is, in fact, the original meaning of the word in English ("moose" comes from the Abenaki language). In an attempt to clear this up, the name "wapiti" has been suggested for the American "elk", although it has never really caught on with the general public. Anyway, whatever you call it, that's the animal I'm talking about here.

But, unfortunately, the confusion doesn't end with the common name - it is also unclear what the scientific name for the animal should be. That's because scientists can't agree on whether or not the elk is a species. Most of the usual sources, such as the IUCN, consider the elk to be merely the American form of the animal Europeans know as the red deer (Cervus elaphus). So, when Europeans say "elk", we usually mean "moose", and when Americans say "elk" they mean a red deer.

Or do they? The elk (or wapiti) has long been thought to be a separate species, and it's only been relatively recently that it has been downgraded to being another type of red deer. There has been considerable argument over whether or not that was the right thing to do. From what I have seen, it very probably wasn't, and the elk likely is distinct enough to be considered a species in its own right. So, I am going to say: the elk (Cervus canadensis) is a large, forest-dwelling deer, native to the northwestern USA and neighbouring parts of Canada, as well as to parts of the Far East.

Red Deer    Elk     Sika Deer
   | |    |
   |         |          |       Thorold's
   | |    |       Deer
   -----------    |    |
| |    |    Sambar,
| |    |     etc.
-----------------    |    ^
|    |    |     Pere David's
|    |    |    Deer, etc.
--------------------    |    ^
|       |    |
|       |    |
---------------------    |
                                    |                    |
                                    |                    |
                                    ----------------------
                                               |
                                               |

The picture may be more complicated even than this. Everyone agrees that the red deer and sika deer are species, and, as I've indicated above, I think there are good grounds for supposing that the elk/wapiti is one as well. It is, however, entirely possible that each of these three actually represents a group of very similar-looking species - for example, the elk of eastern Asia may not be the same as those from America.

The elk of the Blue Mountains live in forests dominated by ponderosa pine, especially around forest edges and clearings. Here, the density of the trees is crucial. Where many trees crowd together, the forest is cast into shadow, which may make it easier to hide small and relatively immobile young. The dappling effect of sunlight coming down through the overhead branches may also be useful in acting as a form of camouflage, in combination with the spotted coats of baby elk. But that same deep shade also means that there is less undergrowth, and it is that undergrowth that supplies the deer's food, as well as potentially hiding predators. So, to get enough food to produce milk for your young, you also have to run the risk of them being eaten.

Elk in this part of the world give birth round about May, so the researchers captured and radio-tagged female elk in March, in the hope of seeing where they would later give birth. They also used a special transmitter that is able to detect when and where an animal gives birth (it is expelled from the body when this happens, and the sudden change in temperature sets it off). Together with the use of GPS, that makes it possible for the researchers to visit the site once the mother and fawn have left, and will no longer be disturbed by their presence - and then you can look and see what sort of location she chose.

When they looked at the areas around those where the mother gave birth, they found that tree cover was lower than average for the surrounding forest, and that the terrain was also slightly flatter. The former in particular would mean greater visibility, perhaps making it easier to spot stalking predators, but it also means that predators were more likely to be there in the first place, suggesting that the availability of plentiful forage was more important than the risk of attack.

However, the deer were choosing their birth sites more subtly than that. Because, when the researchers looked on a much smaller scale at the actual birth sites, those were generally among dense stands of trees or heavy vegetation. In other words, mothers were looking for well-concealed patches in the midst of more open ground - and not, for example, equally secluded dens in denser forest. The tactic seems to work, at least in the short term. For the first four or five days of their life, young elk fawns stay hidden in vegetation or among logs, with the mother patrolling and feeding in the land about them. Yet few of the local predators were eating fawns of that age; if they were looking for them at all, they clearly weren't finding them.

So, for the first five days or so, the fawn is, apparently, quite safe. But that can't last, because sooner or later it begins to get up and follow its mother about, re-joining the herd. Instead of simply hiding, if it needs to escape from a predator after the first few days, the fawn has to run. Once that happened, the balance began to shift. We already knew that most fawns just don't make it to adulthood, as is the case with many wild animals. To find out why that was, the researchers fitted some of the fawns with 'mortality collars' - expandable collars that send out a signal if they don't any sense any movement over a four hour period (if the animal survives, they are designed to eventually fall off anyway, so that they can be retrieved without the need for re-capture).

The primary predators in the area turn out to be cougars and, as expected, they were more successful in open terrain with good visibility. Evidently cover was not a big concern for them; it was more important that they be able to quickly identify elk herds with young and that the latter had little chance to flee deeper into the woods. Of course, we can't tell, just from this study, how often the cougars tried to go after animals in less suitable terrain and failed, but we can see that forest edges, in particular, were good hunting grounds.

So the elk fawns over five days old had a much tougher time of it, although presumably the mere fact of being in a herd, with several vigilant adults, offered at least some protection. But, for the first few days, they are - relatively speaking - safe and cozy, protected not just by the vegetation immediately around them, but by the clearer terrain beyond that where there may be danger, but there is also food for the mother, and maybe a better chance to see what's coming.

[Picture from Wikimedia Commons. Cladogram adapted from DeMiguel et al, 2008]

Weasels on the Farm: Ferrets and Polecats

2011-10-16T14:01:00.001+01:00

European polecats

The great majority of the animals that mankind has domesticated are herbivores; horses, cattle, sheep, camels, guinea pigs, chickens, and so on. Of course, there are always exotic pets, and birds of prey kept for falconry, but when it comes to carnivorous species domesticated for long enough that they are distinctly different from their wild ancestors, there are really only three: cats, dogs... and ferrets.

Of course, ferrets have been domesticated for far less time than either cats or dogs. Quite when this first happened is unclear, although we know that the Romans bred them for catching small animals such as rabbits down burrows, and they may not have been the first to do so. Today, ferrets are often considered sufficiently different from their wild kin to be classed as a different subspecies (just as cats and dogs are). Unlike the wild forms, they are often white or pale yellow in colour, and many are true albinos, with bright red eyes. However, the coat colour can be quite variable, including tan, reddish-brown, dark brown and true black, often with markings that can be clear enough to give a 'Siamese' appearance. Although the colour variation is less than among, for example, cats, the American Ferret Association nonetheless manages to recognise a full 38 possible colour patterns for show purposes.

The wild ancestor of the ferret is the European polecat (Mustela putorius), a darkish brown animal with pale markings on the face. They inhabit forested environments, especially along the banks of streams or rivers, and are common throughout much of western and central Europe. They have fared less well in Britain, being persecuted by gamekeepers in Victorian times, and only beginning to recover after World War I. A sizeable population remains in the Welsh mountains, and has re-colonised parts of England and Scotland, although probably only after some inter-breeding with escaped domestic ferrets. On the other hand, the Scottish polecat may once have been a distinct subspecies, but has been extinct since at least 1912.

While domestic ferrets were originally used for hunting rabbits, these are not a large part of the diet of their wild kin. In most areas, their most common food appears to be frogs, especially in winter, when they can form over 80% of their diet. Of course, they also eat a lot of mice and voles, not to mention the occasional shrew, and some birds, especially where they don't live so close to rivers or ponds. One explanation for the origin of the word "polecat" is that the first half of the word is a corruption of the Old English for "foul", and both polecats and ferrets are somewhat smelly. This smell is important to the animals, giving out sexual signals, with males being particularly interested in the smell of females, and animals being able to distinguish between different individuals on the basis of their odour, and they are wary of scent marks left by animals they don't know.

Further east, we find the steppe polecat (Mustela eversmanii). Where the European species inhabits forests and watercourses, this, as its name implies, has colonised the great open grasslands and plains of eastern Europe and Asia, from the Middle East as far as Mongolia and northern China. Here, in the absence of frogs, much like those European polecats that live far from rivers, it feeds mainly on small rodents, with voles and hamsters being particularly common. In appearance, the two species look quite similar, but the steppe polecat is generally paler in colour, with a more distinct black 'mask' on its face, like that of a raccoon. Indeed, the steppe polecat looks more like a ferret than European polecats do, especially in some subtle features of the shape of the skull. While the genetics of ferrets suggest that they are, indeed, domesticated European polecats, it's entirely possible that at some point, their ancestors were cross-bred with the steppe species, and that the modern form is actually a hybrid.

At some point during the Ice Ages, steppe polecats (or possibly their immediate ancestors) crossed over the Beringian land bridge and entered North America. There, they found new grasslands, and new rodents to eat, and they prospered across the Great Plains. Isolated from their relatives, they developed into a new species, the black-footed ferret (Mustela nigripes), distinguished, as you might imagine, by the colour of its feet. Today, black-footed ferrets eat almost nothing but prairie dogs, although they will catch mice or rabbits if any are around. That can't always have been the case, since the very oldest fossils, found in Nevada, and dating back at least 750,000 years, apparently lived in an area devoid of prairie dogs, but today the fortunes of the two species seem inextricably linked. Without prairie dogs, modern black-footed ferrets just don't seem able to survive.

Which is unfortunate for the ferrets. American farmers are not very keen on having lots of prairie dogs on their land, and, as they eradicated the rodents during the twentieth century, the population of black-footed ferrets crashed. The ferrets generally stay with a particular colony of prairie dogs for much of their life, carefully not eating any more than they need to survive, but, when the rodents are gone, that close relationship becomes a major drawback. So severe was the problem that, for many years, it was thought that black-footed ferrets might well be extinct.

There were always sporadic reports of the animals, however, and, in 1981, the US Fish and Wildlife Service found what appeared to be the last surviving population, hiding out near a ranch in Wyoming. There were barely more than a hundred individuals left alive, and most of them died in 1985 after an outbreak of disease spread among the local prairie dogs, followed shortly thereafter by an outbreak of canine distemper among the ferrets themselves. By the time a captive breeding program was established, the entire world population had dropped to just eighteen individuals.

Black-footed ferret

The species appears to have gone extinct in the wild around 1987, but, fortunately for the ferrets, the captive breeding program has borne fruit. Just four years later, in 1991, the first attempts were made to re-introduce black-footed ferrets to the wild. Most have failed, but three populations, two in Wyoming and one in South Dakota, have become self-sustaining and hold out at least some hope for the survival of the species outside of captivity. They still face problems, however - the living ferrets are genetically inbred (although at least this isn't getting any worse), and many re-introduced ferrets have fallen prey to coyotes and other predators, having apparently lost some of their natural skills during their time in captivity.

All three species of wild ferret are nocturnal, although they will move around during the day if they have to. European polecats are happy to sleep in crevices or hollow logs, and will also occupy burrows dug by other animals. In the more open plains environment of the other two species, burrows are the only realistic option, and, while they don't dig their own from scratch (why bother, when you can get prairie dogs or rabbits to do it for you?) they do often expand the ones they come across to their own liking.

They are, like many mustelids, solitary animals, only coming together to breed in the spring. They give birth to a litter of kits five to seven weeks later, depending on species, just in time for the beginning of summer. Black-footed ferrets seem to have the smallest litters, with typically only about three individuals, although its at least possible that inbreeding really isn't helping here. On the other hand, steppe polecats have an average litter size of seven, and have been known to have up to eighteen kits at a time, although, since they don't have that many teats, it's unlikely that all the members of such exceptionally large litters would survive. The young leave home after about three months, and are ready to mate as soon as their first breeding season comes around the following year.

The pelt of European polecats is considered valuable, and is sometimes sold under the name of "fitch". That of the steppe polecat is much less so, and, indeed, farmers probably gain more from keeping the polecats alive so they can eat rodent pests than they would from trapping them.

All three species can interbreed to produce fertile offspring which, has, naturally enough, raised arguments as to whether they are really different species at all; the current consensus is that they are different enough from each other for that not be an issue. They can even interbreed with their closest non-polecat relative, the European mink, although this appears to be very rare, and the male hybrids are apparently sterile, which is perhaps as well since mink are an endangered species, and wouldn't want to be bred out of existence.

[Pictures from Wikimedia Commons. Cladogram adapted from Koepfli et al. 2008.]

Bats Can Be Colourful, Too

2011-10-09T11:36:00.000+01:00

Spotted bat, Euderma maculata

It's stating the obvious to say that mammals have a range of different colours and coat patterns. The purpose of all these different markings can be varied: they may help to identify members of particular species to their kin, they may be used for sexual attraction, they can act as camouflage, and so on. Nor is there any particular reason to suppose that a given pattern has to serve only a single function. There are a great many colourful mammals, but bats are generally not among them.

The bats are the second largest order of mammals, after the rodents, including a total of nineteen different families - most of them with really obscure names - and well over a thousand different species. Yet, despite this great diversity, most bats are pretty much the same colour all over - usually a variation on the theme of "it's brown". But not all of them; many bats are surprisingly colourful, and you might wonder what the point of that is if they only come out at night, and spend the rest of the day sleeping in pitch black caves. The question really is not so much why are most bats so bland, but why aren't they all that way?

Except, of course, that not all bats do live in caves, and that may well have something to do with it. For the second largest order of mammals, bats have not been as well studied as most other groups. Most of the studies that have been conducted have tended to focus on the undeniably cool fact that bats navigate using sonar. Yet they are a very interesting, and one might even say peculiar, group of mammals. It may be, for example, that just looking at the colours of bats can tell us something about the reasons for coat patterns in mammals in general. A recently published survey by Sharlene Santana of UCLA, and colleagues, examined published descriptions of over nine hundred species of bat, cross-checking the patterns of their fur with their lifestyle. Was there... well, a pattern to the patterns?

The first thing to note is that, yes, most bats are quite bland in terms of their fur colour. Over 80% of the species surveyed are essentially the same colour all over, with no contrasting patterns or shading. Indeed, some families of bats include no species with markings at all. On the other hand, those families are generally very small, with only a handful of species, all of which are, even by the standards of bats, living in much the same way as each other. When it comes to the really large and diverse families of bats - especially the big three of vesper bats, leaf-nosed bats, and flying foxes - while most of them are still bland, we do see a greater variety of coat pattern among those that aren't.

Perhaps the most common colour pattern among mammals in general is a sort of basic counter-shading. The animal is more or less the same colour over most of its body, but it has paler underparts, sometimes quite clearly separated from the darker fur above, but often less so. We see this pattern, for example, in many rodents, but also in a range of species across the mammals. The usual explanation for this is that mammals, being (usually) four-legged, tend to have a horizontal posture. When you see the animal from the side, it's body casts a shadow, so the paler underparts appear visually to be the same sort of shade as the more illuminated upper parts. Which is handy if you're trying to camouflage yourself from predators, for example. Or, if you are a predator, if you don't want your dinner to see you coming.

It turns out that, in bats, this normally common colour pattern is actually quite rare. Less than 5% of the species surveyed had this pattern, at least according to published descriptions and any available photographs. But then, bats don't walk along the ground on four legs. For those that roost in caves, shadows really aren't an issue, and those that roost outdoors aren't doing so horizontally, but are instead hanging head down. In that context, its interesting to note that, while it's still a rare pattern, some tree-roosting bats, especially among the flying foxes, have pale markings on their shoulders and around their neck. If you're hanging upside down from a branch, and light is filtering through the leaves up above, that is exactly where the shadows are going to be, so this may serve the same purpose as more typical counter-shading in other species.

Far more common, however, are those bats with stripes or spots on their bodies, faces, or wings. Sometimes these can be quite colourful and distinctive, as much as those on many more familiar animals. The usual explanation for such bold patterns on animals is that it helps to break up the animal's outline, acting as a kind of camouflage that makes it difficult for predators or prey to easily follow, especially when it's moving rapidly. Zebras and tigers are obvious examples, here. Of course, as I mentioned above, such colours may also be used to signal to other members of their own species, for example, to indicate reproductive fitness. Or, in some cases, even signals to other species; in the case of skunks, the highly contrasting colours seem to be a warning to would-be predators to stay the heck away if they don't want a face full of stink.

Bats have pretty good eyesight, but that's of no use in the pitch blackness of caves. Equally, anything that's going to eat you in a cave won't be confused by contrasting stripes, as it has to be hunting by sound or scent anyway. So, regardless of whether they're using the patterns as camouflage, or as means of identifying each other, we might expect that striped and spotted bats are not the sort to live in caves.

And this is what the survey revealed: cave-dwelling bats tend to be the blandest in appearance, while the most colourful bats tend to roost in vegetation, and not underground. It's not a hard and fast rule, so there may be other factors at play, but there is a definite tendency. Indeed, the bats that just roost in trees by hanging from branches, where they will be hidden by a few conveniently placed leaves at best, are more likely to be striped or spotted than those that go to a bit more effort to hide themselves. For example, some bats actually construct tents out of leaves, so that they are only visible from below. There is some evidence that these bats tend to have stripes on their faces, the only readily exposed parts of their bodies when they're sleeping, although, since we're not talking about a lot of species here, it's hard to prove that that means anything.

So, are these patterns mainly for camouflage? Given the number of species we're talking about, it's unlikely that the answer is always so simple, but there is another indication that it's a pretty major factor. That's because it's not just outdoor roosting bats that are more likely to be coloured, its also those that live in smaller colonies. Bats that live in exceptionally large colonies are at less risk, individually, of being eaten by predators, and they also tend to be larger animals, which means that there are fewer predators able and wanting to eat them anyway. Of course, many of the really big colonies of bats are found in cave-dwelling species, where the colonies may be more populous than most human cities, but the pattern still seems to hold among the more "outdoor" species.

That's not to say that bats can't use coat colours to signal to each other, and at least some of them certainly do. But there's no reason that they can't do both. For example, a solitary, tree-dwelling bat might evolve stripes to hide itself from predators when pressed against the bark, and then also use the same pattern to identify sexual partners when it has to go out and look for some. But, nonetheless, it seems that, if you're a bat, the best way to hide is not to be a bland, boring colour.

Following the Herd

2011-10-01T16:37:00.000+01:00

A number of mammal species live in large groups, including dolphins, monkeys, and wolves, among others. Among the most familiar, though, are the various hoofed herd animals. In order to maintain a herd - or any similarly sized group - it is important that the animals all move together, and that there has to be some kind of communal decision-making process that everyone agrees on. It's no good one animal wandering off on its own, if nobody will follow it, but, equally, if all animals have an equal right to decide where the herd should go, its just going to mill about, not going anywhere.

Undoubtedly, different species will have different methods for making such decisions, depending on their biology, the nature of the environment, and so on. If the group is really big (as might be the case with, say, bison or wildebeest), options are fairly limited, and there is unlikely to be one single leader - if only because not all the members of the herd will be easily able to see him. Among animals that live in smaller groups, leadership by single individuals, or by a small group of individuals, becomes more of a realistic possibility, although alternatives do exist. But which individuals do the leading?

Perhaps surprisingly, there have been relatively few studies of this sort of thing in wild herd animals. Certainly, there have been studies on domestic cattle, and the like, and a number on wild primates, such as baboons. Mathematical modelling using computers, has also been fairly common - a process that has been quite effective at predicting the behaviour of human crowds. But wild herd animals, in wide open countryside, can be fairly difficult to observe. One recent exception is a study by Claudia Ihl, of the University of Alaska Fairbanks, and co-workers, examining one the large ungulates native to that state.

You might think, looking at musk oxen (Ovibos moschatus), that they are some kind of cattle species, perhaps related to yak or buffalo. Indeed, they are members of the cattle family, but then so is almost everything with horns and cloven hoofs, including, for example, gazelles. However, within that family, musk oxen are not true bovines - that is, they are not closely related to bison, domestic cattle, and so on. Instead, the musk ox is the world's biggest species of goat.

Well, perhaps calling it a 'goat' is stretching a point. But it is a caprine, belonging to the same group as the goats and sheep (and a sheep is, biologically speaking, just a goat that can't climb mountains). Essentially, if you make a goat large enough and heavy enough, it's going to look somewhat like a cow, and that's what we have with the musk ox.

Goats,    Chamois,     True      American
etc.       etc.       Sheep   Mountain Goat
^    ^ ^           |
|          |           |           |       Serows       Musk
|    | | |    & Goral     Ox
------------ -------------       ^ |
        |    |           |           |
|    |       | |
        ------------------------                 -------------
   |       |
                   |                                   |
   -------------------------------------
                                     |
                                     |

Exactly how the serows and goral (both from eastern Asia) relate to each other is a little unclear, but there seems little doubt that they are the closest living relatives of musk oxen, despite their much more obviously goat-like appearance. On the other hand, when it comes to the larger groups, the above scheme is not universally accepted, and it may even be that musk oxen are actually closer to goats than 'true' sheep are. I say 'true', incidentally, because there are a number of animals, such as the barbary sheep, that have 'sheep' in their name, but that do not belong to the same evolutionary branch as the domestic sheep and its wild kin.

Musk oxen live in herds of up to forty members, although most seem to average about half this size. They inhabit cold barren environments, with relatively little in the way of vegetation, which makes their decision as to where to seek food particularly important. The herds in this study all live in the Cape Krusenstern National Monument, a region of lagoons, low hills, and long ridges along the western coast of Alaska, dominated by open heathland vegetation. The study took place only during the summer and early autumn, so we don't know whether the animals behave similarly during the winter - when, aside from the cold, there may be as little as an hour and a half of daylight.

Be that as it may, for much of the summer, the herds consist primarily of females and their calves, with just a small number of adult males. The remaining males, presumably, are off on their own, or at best, in small bachelor herds. That changes as the rut approaches, normally around the middle of August. Now those isolated males begin to gather females, luring them away from their existing herds. The end result is that herds are only about half size - ten individuals or so - during the rut, but that each herd contains a higher proportion of adult males.

That the herds are predominantly female, even during the rut, means that, all things being equal, we would expect to see females more likely to be the ones leading a herd off in a new direction. This does indeed appear to be the case, but to an even greater extent than their numerical superiority would suggest. For short movements, in the direction of a tasty-looking patch of tundra grass, this isn't quite so noticeable. True, the females are more likely to be the ones in front when the herd starts moving, but, once you take into account their greater numbers, not by very much.

For longer distance movements, such as heading off in search of an entirely new pasture, the pattern is much more pronounced. For most of the summer, such movements are almost always led by the females, with the males just content to follow. There does not, however, seem to be a single leader for the herd; pretty well any female over two years of age can decide to head somewhere that looks interesting, and have a reasonable expectation that the others will follow.

That it's only adults doing the leading is hardly surprising; they're more likely to know where they're going, and if a calf wanders off, the most sensible thing to do is to fetch it back to the herd before it gets eaten by a wolf or grizzly bear. Yearlings too, don't bother to lead, again most likely due to a lack of experience. But why should the females be more likely to lead than males of the same age?

There may be a couple of reasons here. Firstly, they might be more hungry than the males, having a greater need to keep themselves fit in order to raise young - the so-called 'gastrocentric model'. However, it seems at least as likely to me that baby musk oxen learn to follow their mothers, as well they might, and never quite shake the habit. Musk oxen herds, like those of most other mammals, are based around a core of related females, drawn together by sisterly and motherly bonds, while the males wander off in search of someone they're not related to.

But all of this changes during the rut. Suddenly, the males are more likely to take charge, although they are far from getting their own way all the time, especially when it comes to the longest of movements. But not only are the males more likely to decide where to go, they don't make their decision known in the same way. The females seem to move on a basis of consensus and trust in experience - somebody decides its a good time to move, and the others follow. The males, however, prefer aggression.

Their main motivation here is evidently to stop females leaving them, or worse still, finding another male. If a female tries to leave, they will block her path or chase her about, and continue doing this until she finally gives up, and goes where he wants to instead. Initiating mating may be another tactic to distract the females, but overall, its clear that the males have to go to a lot more effort to get anyone to pay attention to them. For most of the year, they just can't be bothered, but during the rut they have plenty of motivation to keep the females where they can see them.

[Picture from Wikimedia Commons. Cladogram adapted from Laluleza-Fox, et al, 2005 - for an alternative view, see Ropiquet & Hassanin, 2005]

News in Brief #1

2011-09-29T00:46:00.000+01:00

Sometimes weeks go by and I have difficulty finding anything very new to post, at least that isn't too similar to something else I've already done recently. Just as often, though, I have to pick between a number of possible stories, and some end up being pushed to the back of the queue, and never leave it. So, every couple of months or so, I'm going to gather up stories that didn't quite make it, and post a short summary here. So, without any more ado:

Are Foreign Mating Calls Still Sexy?

Sika deer

Mating calls are hardly an unusual feature in mammals, and deer are no exception, especially where the males like to gather a larger number of females around them to mate with. You'd think that part of the point of a mating call is to attract females of your own species, so that you end up with a suitable partner. A group of British, Austrian, and French scientists recently tested this out with female red deer (this is the European version of the animal Americans call an 'elk'). They put up loudspeakers emitting recordings of male red deer, and of male sika deer, a closely related Japanese species with similar mating habits, but that looks quite different.

Sure enough, most of the females wandered over to where the calls of the male red deer seemed to be coming from. But ten percent of the females actually seemed to prefer the calls of the sika males, apparently finding them more enticing than the ones from their own males. The researchers say that this may lead to "permeability of pre-zygotic reproductive barriers"... by which they mean a willingness to have sex with the wrong species. And, indeed, after sika deer were introduced into parks in Europe, some hybrids between the two have been reported. Some red deer does, it seems, just find the exotic attractive.

The Insightful Elephant
We've known for a while that we aren't the only species to use tools, even if we ignore instinctive use of objects - such as birds smashing open snails on rocks. Chimpanzees, for example, have the intelligence to work out how to use simple tools to acquire food, and, outside the world of mammals, even some species of crow have been shown to do the same. Elephants seem a reasonable candidate for another animal that might do the same. They are intelligent animals, and they have a trunk that can pick up and manipulate objects.

With this in mind, researchers from the City University of New York tried to persuade Indian elephants to demonstrate insightful problem solving. Having failed to persuade some Indian elephants to do the obvious primate thing and use sticks to pull down food that was otherwise out of reach, they instead gave them objects they could move into position and stand on, and reach the food that way. Yes, its so basic that it hardly qualifies as a tool, but the fact that one of the males worked out (without any prompting) that this technique would work, shows a degree of problem solving ability not normally seen in non-primate species. He was able to generalise the idea to various other objects, even stacking objects on top of one another when they were not large enough on their own.

Obviously, we can't know exactly what was going on in his mind, but this presumably wouldn't be something he'd normally do in the wild. Perhaps, the researchers suggested, the elephants wouldn't use the sticks to pull down the food (though they were quite happy to use them to, for instance, scratch themselves) because, in those situations, they'd rather use their trunk to feel about, and you can't do that when you're holding something in it. Previous studies on elephants had suggested that, for all their remarkable intelligence in other areas, true problem-solving insight was beyond them. Maybe we just weren't using the right tests.

Two New Rodents
Not all new species reports are as exciting as a new dolphin, but even so, you might be surprised at how common they are, even among mammals - as opposed to, say, insects, where there must be a vast array of beetles and so forth out in the jungles that we haven't seen yet. The June issue of the Journal of Mammalogy reports two potentially new species. Dolphins aside, I've mentioned before how fraught this can be, and there's a lot of argument over what a species actually is, let alone how to find one, so we can't be sure these will stand the test of time, but I think they're still worth looking at.

The first comes from India. Here we have what appears to be a subspecies of the familiar black rat, also called the ship rat, house rat, and so on, and second only to the slightly larger brown rat in its ability to follow humans around the globe. Unlike the other black rats nearby, this subspecies has a white belly, but its otherwise pretty much identical. Nonetheless, French researchers have concluded, after an examination of their genetics and biochemistry that they are not merely a subspecies, but an entirely separate species, living alongside the 'real' black rats in the dense forests of the Nilgiri Hills. There is, they argue, no evidence that the two interbreed, despite having every opportunity to do so - presumably, they have a better method than blood-testing to tell each other apart.

The second species, Cerradomys goytaca, is a type of marsh rat from the coasts around Rio de Janeiro. It looks pretty much like any other rat, although, like most rats and mice native to the Americas, its actually a member of the hamster family. Although the researchers do report distinctive genetics, they also provide a detailed physical description that makes it possible to tell the animal apart from all of its related neighbours. It is slightly larger, with a wider snout and thinner hair than any of the three species already known, and inhabits shrubby subtropical forests along a relatively narrow stretch of the Brazilian coastline.

New Fossils Reported
I'll admit it - two of these are rodents as well, although neither of them are rats. The first is a ground squirrel that lived, around seven million years ago, on the north shores of Lake Chad - then much larger than it is now. It appears to have died when its burrow collapsed, possibly in a flood, and the shape of its teeth suggests that it would have eaten hard fruit, presumably in an open forest or savannah environment. It's significant because it would have lived alongside Sahelanthropus, the oldest known member of the African ape subfamily to which we ourselves (along with chimps and gorillas) belong. Being able to tell how this squirrel lived therefore gives us some insight into the environment of one of our own early relatives.

From about a million years later, and far away in Myanmar, comes a fossil porcupine. All they have is a small piece of the lower jaw, but even that shows that the animal would have been larger than any other known porcupine in the area (unless it had a particularly large head, which seems unlikely). The shape of its teeth suggest an adaptation to an increasingly dry habitat, dominated by grassland, unlike the jungles of today, something that fits with our understanding of past climate change in the area.

Rather more dramatic, perhaps, is a far older fossil, of an animal that lived in Wyoming as much as 40 million years ago. Again, we only have a jaw, although that's nearly a foot long, which suggests a fair-sized animal. The jaw probably belongs to some sort of tapir-like creature, although its sufficiently odd that that's difficult to say for sure. It doesn't seem to be closely related to anything else that we know of, and perhaps represents some otherwise lost lineage only distantly related to the true tapirs.

[Picture from Wikimedia Commons]

A New Species of Dolphin

2011-09-25T17:12:00.000+01:00

Common bottlenose dolphin

On September 14th, the discovery a new species of dolphin, the burrunan dolphin (Tursiops australis) was officially announced. There has already been a fair bit of coverage of this in the media (see, for example, the BBC story), but I want to focus here on how this all came about. How exactly do you go about naming a new species?

In theory, it's a fairly straightforward, if somewhat laborious, process. You find your new species, write up a description of what it looks like, and how to tell it apart from similar species, designate a holotype (more on this later), think up a name, and get it published. Leaving aside the difficulty of the first part of that - "first, find your new species" - that's often all there is to it. But, with dolphins, the story has been rather more complicated than that.

First, let's get our bearings. The sort of dolphin we're talking about here is a bottlenose dolphin, a particularly well known type, and commonly seen in sea mammal parks, where they have been trained to perform a number of tricks. They live in every ocean, avoiding only the very coldest of polar seas and are therefore extremely widespread.

The common bottlenose dolphin was first formally described by George Montagu in 1821, and given the scientific name Delphinus truncatus, which means something like "shortened dolphin", and refers to the relatively short snout. A second species, the Indo-Pacific bottlenose dolphin, was identified in 1832. Paul Gervais, in 1855, in the process of naming a third species, decided they were different enough to be given their own genus: Tursiops - a name borrowed from the Latin for "porpoise".

Over the next eighty years, more and more species of bottlenose dolphin were named, largely on the basis of "well, they look a bit different". In the days before genetic analysis, this was all fairly reasonable. It is, after all, difficult to see exactly which groups of dolphins are inter-breeding, since they're out at sea when they're doing it. At least four of the named species had scientific descriptions that were too vague for us to know what it was the author was trying to describe, but that still left at least eight, and possibly as many as twenty, species.

This all looked to be cleared up when it was decided that there was really only one species, that just happened to have a rather variable appearance. Because it was the first, the 1821 description and name stood, and all of the others were just newer names for the same thing - subspecies, at best. But this, it turned out, was very far from being the final word: in 1998, it was determined that the Indo-Pacific bottlenose dolphin really was a separate species from all the others, and so its species was resurrected, as Tursiops aduncus.

So, we have two species of bottlenose dolphin, the common and the Indo-Pacific. But were some of those nineteenth and early twentieth century naturalists right? Were at least some of the species they named real all along? Into this muddied picture swims the newly discovered species.

As you may have guessed, this is not an animal that nobody had ever seen before. We had seen plenty of them, off the coasts of southern and eastern Australia, but had assumed that they were just members of one of the other two species - though it wasn't very clear which. Indeed, it was one of the many groups previously suggested to form its own species, named the "southern Australian bottlenose dolphin" (Tursiops maugeanus).

When you name a new species, one of the things you have to do is identify a holotype; a particular specimen of your new animal. More than that, it is the crucial, defining specimen of the animal. It is the one specimen that you can, if need be, point to and say "this is what I'm talking about". If it later turns out that your species is really two or more different species, the name you chose stays with the species that the holotype belongs to, because that's the one you were really describing. On the other hand, if it turns out that your holotype isn't really a new species, then your chosen name is worthless, and cannot be used from them on, at least as any more than a subspecies.

So, when the authors of this paper wanted to prove that the southern Australian bottlenose really was its own species, one of the things they did was to take a look at the holotype specimen originally designated back in 1934. Problem is, there wasn't one. In those days, the rules had been less strict, and the scientists who had originally described the species noted that one of the interesting things about it was that the males and females looked quite different, something not so unusual among mammals. So they decided to designate not one, but two, type specimens, one male and one female. This, they hoped, would avoid all confusion.

But they were wrong.

Because, when the modern scientists analysed the DNA of the two specimens, they discovered that there was a very good reason that the male and female looked different: they weren't the same species. Which is precisely why, of course, you aren't supposed to designate more than one type specimen these days - fine though it was in the 1930s. The male, so far as they could tell, was just a common bottlenose dolphin, but the female seemed to be something else entirely. From genetic samples taken from a number of living and recently dead dolphins in the general area, they identified that she was closely related to a group of dolphins found off the coasts of Victoria, South Australia, and Tasmania - and nowhere else.

But that wasn't really enough to prove that she, and her living relatives, belonged to a new species. They were something distinct, certainly, but were they distinct enough? There are many different ways to define a species, and the authors of this new paper decided to cover their bases by describing their species in as many different ways as they could.

They delved into the genetics to demonstrate that the dolphins were so different from other bottlenoses that they couldn't be anything but a new species. But genetics wasn't enough. There has been so much confusion over how many species of dolphin there really are that there's an informal agreement among scientists dealing with these animals that, before they'll agree you've found something new, you need both genetics and the ability to prove you can tell your animal from others just by looking at it. Either one on its own just isn't enough; it's a stricter rule than is applied with most other mammals, but it does make things rather more certain.

The new species is much smaller than the common bottlenose dolphin, and somewhat larger, on average, than the Indo-Pacific species. Like the common species, but unlike the Indo-Pacific, it has a short, stubby snout, and a curving, rather than triangular, fin on its back. Unlike either form, it has a bluish-grey upper body, with a distinct pale grey stripe along its flanks, and a whitish underside and face, without any of the spots sometimes seen on other dolphins. There are also some noticeable differences in the skull, especially in the shape of the bones of the upper jaw, that are described as being quite unlike those of either of the other known species.

Examining the DNA to determine how the new dolphin relates to other species reveals some of the complexity that has made the classification of the dolphin family so difficult:

Burrunan   Spinner
Bottlenose Dolphin
Dolphin |           Common
     |          |           Bottlenose
     |          |   Fraser's Dolphin
     ------------   Dolphin,    |
          |           etc.        |    Indo-Pacific
          |            ^        |     Bottlenose    Clymene
          |            |          |      Dolphin      Dolphin,
          |            ?          |         |          etc.
          -------------------------         |           ^
                        |                   |           |
                        |                   |           |
                        |                   -------------
                        |                         |
                        |                         |
                        ---------------------------
                                     |
                                     |

Text in blue shows members of the genus Tursiops. Text in green shows the genus Stenella.

Notice that there's something very wrong about this chart. Not only does it show that the new species isn't particularly close to the common bottlenose, being closer to the Spinner dolphin (Stenella longirostris), but the two species of bottlenose dolphin that we already knew about aren't related to each other, either. This actually wasn't a great surprise; we'd already guessed as much, and this new discovery only makes things a little bit worse.

However, what you can't tell from this simplified version of the original is just how tiny some of the genetic differences are. Its not that the species aren't clearly different from one another - they are - its that most of them are different by almost exactly the same amount, which means that its very hard to tell in what order they would have branched apart. Quite where Fraser's dolphin goes isn't clear at all, for instance, and some of the others are nearly as uncertain.

Somebody, at some point, is going to have sort this mess out, but it hasn't happened yet, and the authors decided to leave their new species in Tursiops for lack of anything more obvious to do with it. They don't expect it to stay there, and went as far as to suggest a name for the new genus they would like it placed in when somebody finally works out what is going on with dolphin relationships.

So, having proven that we've found a new species, what do we call it? If it was completely new to science, the authors could just make their own name up, but, remember this one was first identified back in the 1930s. You might think therefore, that they'd just use the old name, which is exactly what happened when the Indo-Pacific bottlenose was resurrected from taxonomic oblivion. I get the impression that the authors argued quite a lot about this, since it depends on what you're doing with the holotype - and there isn't one.

Their eventual decision, which is probably fairly arguable, was that the original scientists had been describing the male specimen more than the female. Since the male isn't a member of their new species, they got to think up a new name, and, being Australian, chose Tursiops australis. The female, which died in the North Esk River in 1914, and currently resides in a museum in Launceston, was designated as the holotype of the new species.

If it's not quite the same thing as was described back in 1934, they don't have to continue calling it the 'southern Australian bottlenose dolphin', either. Instead, they chose 'burrunan dolphin' as the common name, borrowing the local aboriginal word for 'dolphin'. This common name has no particular scientific standing, and is just a suggestion, but it's likely the name that will stick.

The final step in naming a new species is to have the description officially published. Yet even that presented a bigger hurdle than it should have done, for they chose to publish in the online electronic-only journal PLoS ONE. But the ICZN, the international body that handles the naming of new animal species, has yet to enter the twenty-first century, and refuses to accept that anything electronic can really have been published. So they had to go to the trouble of producing a separate print-on-demand version and posting it to key libraries before anyone was allowed to pay attention to what they'd written.

The end result of this complex, messy, story is that we have a new species of dolphin, living off the coast of south-eastern Australia that we kind of knew about, but had never been formally described before. Given all the confusion that has reigned since the first bottlenose dolphin was described almost two hundred years ago, it won't be the last. There are more species of dolphin out there to be found, and it probably won't be too long until we hear about them.

[Picture from Wikimedia Commons. Cladogram adapted from Charlton-Robb, et al. 2011]

Griphotherion - the Puzzling Beast

2011-09-18T13:49:00.000+01:00

The skull of Mesotherium, a large, beaver-like, typothere

- note the shape of the teeth

For millions of years after its separation from Antarctica and before its collision with North America, South America was an island continent, isolated from much of the rest of the world. Many of the groups of mammals we are familiar with had not evolved at the time of the separation of the continent, and its long period of isolation allowed many strange animals to evolve to take their place, quite different to those elsewhere in the world.

Once Central America began to form, and the animals we are more familiar with began to flood south, these odd native animals began to die out. It took a long time, and, in fact, four groups do still survive today - opossums, armadillos, anteaters, and sloths are all remnants of this once more diverse group, and two of those even crossed the land bridge in the other direction, and can now be found in the North.

But the others were less fortunate. Large carnivorous mammals never got a foothold in the continent when it was still an island, and the arrival of sabretooths and the ancestors of jaguars (to name two obvious examples) doubtless contributed to the decline of the native fauna. Herbivores, however, were a different matter. I've mentioned this before, in the context of some rather odd-looking long-nosed herbivores, but there are many other examples.

The single most successful group of these long-gone herbivores were the notoungulates. We know of over a hundred species of notoungulate, in multiple different families and they were once as important in South America as antelopes are in Africa. They were, for the most part, hoofed animals, although quite unrelated to the hoofed animals we have today (and some did, in fact, have claws, instead). Like horses, and unlike cattle, they placed most of their weight on the enlarged middle toe of each foot. However, unlike horses, they never entirely lost all of the other toes, and most had three hooves on each foot.

Some older books, incidentally, will tell you that the notoungulates briefly succeeded where most of their neighbours failed, and managed to spread into North America, and even as far as China, before finally dying out. We used to think that was the case, but it turns out that the fossils in questions were victims of mistaken identity, and that, while at least one species did make it as far as Central America, there is no evidence that they ever got any further.

The notoungulates can be divided into three broad groups; the primitive notioprogonians, the giant toxodonts, and the typotheres. Where the toxodonts took on a role not dissimilar to that of the antelopes and rhinos elsewhere, the typotheres evolved to fill a different, but equally vacant, herbivorous niche - they came to resemble rodents.

They were generally larger than rodents, though - most were at least rabbit or cat-sized, and a few reached the size of pigs. The early notoungulates had the full set of 44 teeth found in all the earliest placental mammals, albeit adapted for their herbivorous diet. The typotheres, however, eventually lost the canine teeth, and reduced the incisors to a single large, chiselling pair at the front of the mouth, separated by a gap from the chewing cheek teeth further back. This is the same pattern we see in rodents, and suggests that they had a similar diet. One group even had exceptionally long hind legs, suggesting that they may have leapt about like rabbits (rabbits are not rodents, of course, but they have a similar lifestyle).

We can also tell that they probably had very acute hearing. This is because one of the most distinctive features of their fossils is the presence of a greatly enlarged ear region in the skull, with an additional cavity in the bone and a detailed structure not found in other animals.

A new species of typothere has recently been described by Daniel García López and Jaime Powell of the National University of Tucumán in Argentina. The fossil includes an unusually complete skull, which is about 7 cm long, suggesting a fairly small animal of its kind. It dates from the middle of the Eocene, the second and longest epoch of the Age of Mammals, a time before many modern groups of mammal had evolved, and long before the two American continents joined up. The skull is rounded, with a short snout and large eye sockets.

As might be expected, given the age, the new species is a relatively primitive member of its group. Of course, the term "primitive" isn't really a very good one, and the animal would doubtless have been well adapted to doing whatever it did in its native habitat. What it means here is that the animal had changed relatively little from its ancestors, still keeping many of the features that they had had, rather than those that would be developed later on.

For example, it still has the full set of teeth, including the canines and the second and third incisors that are absent in some more advanced forms, although the first pair of incisors do already have the chisel-like shape that makes them resemble those of rodents - those in the upper jaw are also larger than the other incisors. From this, we can infer that the animal was already developing the diet and habits that would be shared by later forms, which is how we know it's a typothere at all.

The overall range of features in the skull is somewhat odd; they present a mixture that makes it impossible to assign the fossil to any of the four or five known families of typothere. That's not unusual when you have an incomplete or damaged fossil, as often happens - you might have enough to say that your animal is a new one, but still be missing some of the crucial bits needed to work out what it was most closely related to. That's not the case here - we do have the relevant pieces, they're not just not telling us a consistent story, based on what we already know. As a result, the animal was christened Griphotherion peiranoi; the first part of the name meaning something like "puzzling beast".

The most likely explanation is that Griphotherion is a genuinely primitive form. It might not literally be the ancestor of later typotheres, but it's at least closely related to whatever was. Later on, in the Oligocene, the descendants of such animals began to branch into the many forms of typothere that populated the continent, from the heavily-built Mesotherium (shown in the picture above), to the rabbit-like Hegetotherium and the coney-like Archaeohyrax. It thus represents a "bridge" between the genuinely primitive forms, and those that more closely resembled rodents and rabbits.

Due to the presence of a range of other primitive and early notoungulates in the same area, the authors argue that north-western Argentina may be the origin point in which the first members of this once important group of animals began to diversify into their many later forms. That may, perhaps, be narrowing it down a little, for one suspects that, even in the Eocene, they must have travelled across a reasonable chunk of the continent, but it does seem to be the case that these fossil deposits have a lot to tell us about the beginnings of a parallel path in the evolution of large mammalian herbivores, an equally viable alternative to the ungulates that we still have today.

[Picture from Wikimedia Commons]