Not Exactly Rocket Science

South African wildlife - Wait, that's not a trunk...

Sat, 07 Nov 2009 08:00:38 -0500

This is a bull elephant firmly establishing why it is he, and not the lion, who is king of beasts. The elephant's penis is not only massive but prehensile. As we watched in baffled amusement (and the faintest tinge of inadequacy), he used his penis to prop himself up (as in the photo), swat flies from his side and scratch himself on his stomach. David Attenborough never showed us that...

There's good reason for elephants to have prehensile penises. It's hard enough for a six-tonne animal to get into the right position for sex, let alone having to do the rhythmic thrusting that's required. So he let's his penis do all the work for him.

You'll also note the dark stain behind his eye - that's a leak from his temporal gland. It means that this male was entering musth, the period when their testosterone shoots through the roof and they get incredibly horny and aggressive. We tried to drive round this male and he basically charged us. Tramply doom was averted by our driver who slammed his palm against the car door as hard as he could. The elephant stopped and huffed and puffed. We did our best to not soil ourselves.

This picture gives you an idea of how close he was. After a seemingly infinite standstill, he moved aside, extended his enormous penis and had a wee. It's amazing how terror can convert into comedy so quickly...

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Discriminating butterflies show how one species could split into two

Thu, 05 Nov 2009 14:00:01 -0500

Walk through the rainforests of Ecuador and you might encounter a beautiful butterfly called Heliconius cydno. It's extremely varied in its colours. Even among one subspecies, H.cydno alithea, you can find individuals with white wingbands and those with yellow. Despite their different hues, they are still the same species... but probably not for much longer.

Even though the two forms are genetically similar and live in the same area, Nicola Chamberlain from Harvard University has found that one of them - the yellow version - has developed a preference for mating with butterflies of its own colour. This fussiness has set up an invisible barrier within the butterfly population, where traits that would typically separate sister species - colour and mate preferences - have started to segregate. In time, this is the sort of change that could split the single species into two.

Heliconius butterflies defend themselves with foul chemicals and advertise their distasteful arsenal with bright warning colours on their wings. The group has a penchant for diversity, and even closely related species sport different patterns. But the butterflies are also rampant mimics. Distantly related species have evolved uncanny resemblances so that their warnings complement one another - a predator that learns to avoid one species will avoid all the ones that share the same patterns. It's a mutual protection racket, sealed with colour.

The result of this widespread mimicry is that populations of the same species can look very different because they are imitating different models. This is the case with H.cydno - the yellow form mimics the related H.eleuchia, while the white form mimics yet another species, H.sapho.

How can we be sure that the pairs of butterflies that look alike aren't in fact more closely related? For a start, scientists have shown that the frequencies of the yellow and white versions of alithea in the wild match those of the species they mimic. Genetic testing provides the clincher. It confirms that the two mimics are indeed more closely related to each other than they are to their models.

Genetics also tells us how alithea achieves its dual coats. Colour is determined by a single gene; if a butterfly inherits the dominant version, it's white and if it gets two copies of the recessive one, it's yellow. Pattern is controlled in a similar way by a second gene. These variations aside, there are no distinct genetic differences between the two alithea forms. They are still very much a single population of interbreeding butterflies.

But that may change, and fussy males could be the catalyst. Chamberlain watched over 1,600 courtship rituals performed by 115 captured males. Her voyeuristic experiments showed that yellow males strongly preferred to mate with yellow females, although white males weren't so fussy.

This isn't just a whimsical preference - Chamberlain thinks that the colour gene sits very closely to a gene for mate preference. The two genes may even be one and the same. Either way, their proximity on the butterfly's genome means that their fates are intertwined and they tend to be inherited as a unit. That's certainly plausible, for the same pigments that colour the butterflies' wings also serve to filter light arriving into their eyes. A change in the way those pigments are produced could alter both the butterfly's appearance and how it sees others of its kind.

To see what happens when this process goes further, you don't have to travel far. Costa Rica is home to another H.cydno subspecies called galanthus, and a closely related species called H.pachinus. They represent a further step down the road that alithea is headed down. Galanthus and H.pachinus look very different because they mimic different models - the former has white wingbands reminiscent of H.sapho, while the latter has green bands inspired by H.hewitsoni.

Nonetheless, the two species could interbreed if they ever got the chance. Two things stand in the way. The first is geography - H.cydno galanthus stays on the eastern side of the country, while H.pachinus remains on the west. The second is, as with alithea, sex appeal. Males prefer females bearing the same wing colours as they do so even if the two sexes of the two species were to cross paths, they'd probably fly right past each other.

Genetically, these species have also diverged far further than the two forms of alithea have. They differ at no less than five genes involved in colour and pattern, two of which are practically identical to the ones that causing alithea to segregate. They also provide more evidence that the genes for colour and mate preference are closely linked, for crossbreeding the two species yields offspring with half-way colours and half-way preferences.

These butterflies are by no means the only examples of speciation in the wild. In this blog alone, I've discussed a beautiful case study of diversity creating itself among fruit flies and parasitic wasps, explosive bursts of diversity in cichlid fish fuelled by violent males, and a giant predatory bug that's splitting cavefish into isolated populations.

But Heliconius butterflies may be the most illuminating of all these case studies. They're easy to capture, breed and work with. And as Chamberlain's study shows, they can marshal together the contribution of experts in genetics, ecology, evolution and animal behaviour in an effort to understand that most magnificent of topics - the origin of species.

[This post was written as an entry for the NESCENT evolution blogging contest. For more details about this competition, visit their website.]

Reference: Science 10.1126/science.1179141

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Native language shapes the melody of a newborn baby's cry

Thu, 05 Nov 2009 12:00:15 -0500

Telling the difference between a German and French speaker isn't difficult. But you may be more surprised to know that you could have a good stab at distinguishing between German and French babies based on their cries. The bawls of French newborns tend to have a rising melody, with higher frequencies becoming more prominent as the cry progresses. German newborns tend to cry with a falling melody.

These differences are apparent just three days out of the womb. This suggests that they pick up elements of their parents' language before they're even born, and certainly before they start to babble themselves.

Birgit Mampe from the University of Wurzburg analysed the cries of 30 French newborns and 30 German ones, all born to monolingual families. She found that the average German cry reaches its maximum pitch and intensity at around 0.45 seconds, while French cries do so later, at around 0.6 seconds.

These differences match the melodic qualities of each respective language. Many French words and phrases have a rising pitch towards the end, capped only by a falling pitch at the very end. German more often shows the opposite trend - a falling pitch towards the end of a word or phrase.

These differences in "melody contours" become apparent as soon as infants start making sounds of their own. While Mampe can't rule out the possibility that the infants learned about the sounds of their native tongue the few days following their birth, she thinks it's more likely that they start tuning into the own language in the womb.

In some ways, this isn't surprising. Features like melody, rhythm and intensity (collectively known as prosody) travel well across the wall of the stomach and they reach the womb with minimum disruption. We know that infants are very sensitive to prosodic features well before they start speaking themselves, which helps them learn their own mother tongue.

But this learning process starts as early as the third trimester. We know this because newborns prefer the sound of their mother's voice compared to those of strangers. And when their mums speak to them in the saccharine "motherese", they can suss out the emotional content of those words through analysing their melody.

Mampe's data show that not only can infants sense the qualities of their native tongue, they can also imitate them in their first days of life. Previously, studies have found that babies can imitate the vowel sounds of adults only after 12 weeks of life, but clearly other features like pitch can be imitated much earlier. They're helped by the fact that crying only requires them to coordinate their breathing and vocal cord movements, while making speech sounds requires far more complex feats of muscular gymnastics that are only possible after a few months.

Reference: Current Biology doi:10.1016/j.cub.2009.09.064

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Mid-continent earthquakes are often aftershocks of centuries-old tremors

Wed, 04 Nov 2009 13:00:04 -0500

Small earthquakes in unexpected locations are often a cause for concern. The worry is that these rumbles are harbingers of bigger quakes to come. But not always - a new study suggests that many of these tremors aren't warnings, but aftershocks. In particular, those that happen in the middle of continents, far away from the major fault-lines that separate tectonic plates, probably reflect past quakes rather than future ones.

Earthquakes are a common occurrence on the boundaries between tectonic plates, and they occur at predictable spots. But they can often strike areas that are far away from such boundaries and where old fault-lines have seen little seismic activity over the past hundred years. The central United States, for example, experiences many such unexpected tremors.

But Seth Stein from Northwestern University and Mian Liu from the University of Missouri think that many of these small quakes are aftershocks of two bigger magnitude-7 tremors that shook the Midwest around 200 years ago.

The first hit a town called New Madrid in 1811 and triggered three shocks of similar magnitude that, together, reactivated an ancient set of faults in the continent's interior. The second big one hit Charleston, South Carolina in 1886. Low-level seismic activity in both areas, New Madrid and Charleston, is often interpreted as a sign that they will once again be hit by large earthquakes in the future, painting two imaginary bull's-eyes of risk in middle America.

New Madrid afer the 1811 quake

Large earthquakes are often followed by aftershocks, the result of changes in the surrounding crust brought about by the initial shock. Aftershocks are most common immediately after the main quake. As time passes and the fault recovers, they become increasingly rare. This pattern of decay in seismic activity is described by Omori's Law but Stein and Liu found that the pace of the decay is a matter of location.

At the boundaries between tectonic plates, any changes wreaked by a big quake are completely overwhelmed by the movements of the plates themselves. At around a centimetre per year, they are regular geological Ferraris. They soon "reload" the fault, dampen the aftershocks, and return the status quo within 10 years. In the middle of continents, faults move at less than a millimetre every year. In this slow lane, things can take a century or more to return to normal after a big quake, and aftershocks stick around for that duration.

Stein and Liu's study could help scientists to more accurately predict the risk of future earthquakes, especially in unexpected areas. If they're right, then it would be positively misleading to base such assessments on small quakes that could sometimes be aftershocks of historical events. In the longer term, Stein and Liu predict that such approaches will "overestimate the hazard in some places and lead to surprises elsewhere". The disastrous earthquake that hit China's Sichuan province in May 2008 highlights the catastrophic impact that unexpected mid-continent quakes can have.

To begin with, we need to better understand the network of faults that criss-crosses continents. Fortunately, such work is already underway. Palaeoseismology - a field of research that reads traces left by prehistoric earthquakes - is providing a much longer history of tremors than our pitifully short records do. Meanwhile, GPS mapping can reveal places where plates are being deformed. These are the sorts of data that will allow us to separate the aftershocks of earthquakes past from indicators of future quakes.

Again, New Madrid proves the principle - a cluster of large earthquakes hit the area in the past thousand years, but the crust shows no sign of recent deformation according to two decades of GPS measurements. It seems that recent activity really is the legacy of centuries-old quakes, a threat that has since shut down.

Reference: Nature doi:10.1038/nature08502

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Even without practice, sleep improves memory of movements

Wed, 04 Nov 2009 08:30:51 -0500

When we think of memory aids, we consider repeating what we've learned, using clever mnemonics, or breaking information down into bite-size chunks. But one of the best memory aids we have available to us is something we all do on a daily basis - sleep. Studies have found that sleep enhances our memories of facts and physical skills alike. It can even help us remember movements that we see others do.

But this only works within a short window. Ysbrand van der Werf from the Netherlands Institute of Neuroscience found that people who saw a video of someone tapping keys on a laptop remembered the sequence more accurately if they slept on it within 12 hours. Any longer than that, and the snoozing didn't boost their recall.

Van der Werf showed the video to 128 volunteers and then tested them on either the same finger-tapping sequence or a different one. The gap between video and test was either 12 or 24 hours, and some of the volunteers were allowed to sleep during the interval while others were not.

If the test sequence didn't match the ones they saw, all the recruits did equally well. But if the sequence was the same, those who managed to sleep within the first 12 hours stood out - they were 22% faster and made 42% fewer errors than their peers who either didn't sleep or who slept later. They even improved whether they had their naps during the day or in the evening.

These results parallel those from experiments where people actually had a chance to practice new skills before their naps. The big difference here is that the improvements came only after watching movements rather than actually performing them.

Van der Werf confirmed that by taking great care to ensure that his volunteers weren't actually trying out the keystrokes for themselves. While watching the video, they had to tap two different keys to keep their fingers busy. Van der Werf even measured the muscle activity in the arms of seven volunteers to rule out the possibility that they were making subtle, unnoticed finger movements.

If it's not to do with practice, it's not to do with memorising the digits themselves or the position of the keys either. If the volunteers just saw the numbers flash up on screen, or if they saw coloured squares light up in the same position as the relevant keys, they didn't become more accurate or faster when they had to replicate the sequence. They needed to actually see someone else doing it.

Van der Werf thinks that the recruits probably imagined their finger movements while watching the video, even if they didn't actually try them out. It may even involve the mirror neurons that fire when an individual performs an action and when it sees someone else doing the same action (although mirror neurons have only been properly found in monkeys, and not humans).

Either way, the results highlight the importance of a good sleep when people are trying to pick up new physical skills. This could be especially important for people who can't possibly to practice the movements in question, such as those who have suffered a stroke or broken a limb. And clearly the most important implication is that the next time I see someone doing parkour, I will immediately lie down and have a little nap. When I wake up, I will be Batman. SCIENCE!

Reference: PNAS doi:10.1073_pnas.0901320106

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In a pandemic climate, public sneezing increases fears of unrelated risks

Tue, 03 Nov 2009 07:45:44 -0500

A friend of mine recently got onto a train and found a group of four seats that were empty except for one woman who was sitting face down. She looked asleep and he looked forward to a quiet journey. As soon as he sat down, the woman lifted her head to reveal streaming, puffy eyes and started sneezing profusely. This happened a few weeks after swine flu first began to dominate the headlines but being English, he was bound to the socially awkward choice of staying in his seat for the sake of avoiding social awkwardness.

Many of us probably have similar stories. At a time when fears of a flu pandemic dominate the headlines, does an innocuous sneeze make people fear the worst? Perhaps, but a new study suggests that hearing someone else sneeze plays with our minds far beyond exaggerated worries about pandemics. They can make us more worried about completely unrelated threats like heart attacks, crime and accidents. They can even affect our political attitudes.

On May 7, 2009, when swine flu had spread to at least 24 countries, a group of researchers from the University of Michigan took it upon themselves to sneeze in front of passers-by on their campus. Led by Spike Lee (no, not that one), the team approached 26 people who had heard the sneeze and 24 controls who hadn't, and asked them to complete a questionnaire for a class project.

Compared to the control group, those who had heard the sneeze felt that "average Americans" were more likely to contract a serious disease, citing risks of 41% compared to just 27%. More surprisingly, they also gave significantly higher estimates for the risk of dying from a heart attack by the age of 50 or of dying from crime or accidents. They even had slightly less faith in US healthcare, although this difference wasn't statistically significant.

Later on in the month, when almost twice as many countries had been infected, Lee performed a similar experiment in a shopping mall. This time, the experimenter asked passers-by to take part in a one-minute survey. Twenty-four of the volunteers received the form without much ado. Another 23 were handed the form by an experimenter who pretended to cough and sneeze at the same time, while covering her mouth with her forearm.

The first question asked people if they would prefer the federal government to allocate $1.3 billion towards the production of flu vaccines or the creation of green jobs. Faced with a sneezing, coughing researcher, almost half (48%) of the volunteers chose to finance the vaccine. Without the symptoms, only 17% did.

Of course, it's possible that being handed a form by a spluttering individual just put the volunteers in a negative and grumpy mindset. But Lee thinks not - a second question about the general direction of the country showed that both groups of volunteers were, on the whole, equally ambivalent about it.

Lee suggests that a minor, everyday event (like a sneeze) can heighten our worries about a whole range of unrelated hazards because it brings to mind a prominent threat (like a flu pandemic). Our emotions are affected by our ability to assess risks, regardless of what those risks are. In this way, the feelings elicited by one threat can feed into our evaluation of others, and sneezing in a pandemic climate can make people more worried about unrelated hazards from heart disease to crime.

Obviously, there's more work to be done. Lee's team haven't actually demonstrated that sneezing in a pandemic era makes people more worried about that specific threat. It would also be interesting to see if the effect they found waxes and wanes over time, and how that related to the amount of concurrent media coverage .

Nonetheless, one thing is clear. Like many aspects of our minds, people are completely unaware of this effect. When asked later, the volunteers didn't twig to the aims of the experiments. And while they assumed that a sneeze could make them overestimate the risk of flu, they didn't think it would make them think differently about the odds of other threats.

Reference: Psychological Science, in press.

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How many people did the man-eating lions of Tsavo actually eat?

Mon, 02 Nov 2009 17:00:32 -0500

In 1898, railway workers in Tsavo, Kenya were terrorised by a pair of man-eating lions, who killed at least 28 people during a 10-month reign of terror. It ended in December when a British officer called Lt. Col. John H. Patterson killed both beasts. The man-eaters' notorious exploits have been immortalised in no less than three Hollywood films, including most recently The Ghost and the Darkness. But despite their fame, no one is quite sure how many people they killed. The Ugandan Railway Company said 28; Patterson claimed it was 135.

Both parties had reasons to lie, either playing down or exaggerating the figures for the sake of reputation. But Justin Yeake from the University of California decided to find the truth by going straight to the source - the remains of the man-eaters, currently on display in Chicago's Field Museum of Natural History. By studying the chemical composition of the lions' hair and bones, Yeake estimated that they killed around 35 people, with a possible range of 4 to 72. Either way, Patterson's claim was wildly exaggerated.

The Tsavo man-eaters at the Chicago Field Museum, taken by Jeffrey Jung

Yeake took samples of the lions' bone collagen and hair keratin, and measured the ratio of carbon and nitrogen isotopes. Both can tell you about the items on a lion's menu - bone collagen grows slowly and reflects the lion's lifetime eating habits, while keratin from fast-growing hairs reveals the nature of its meals over the past three months.

Yeake compared these ratios to those of modern Tsavo lions, and matched them against those form various prey animals including giraffe, kudu, impala, zebra, buffalo and humans. The human samples came from remains collected by anthropologist Louis Leakey during his East African Archaeological Expedition of 1929.

The results showed that the diet of Tsavo's modern lions consists almost entirely of grazing animals such as zebra, waterbuck and buffalo. The man-eaters were different. Yeake calculated that one of them probably ate around 11 people in its nine-month hunting spree, but focused mainly on expanding its tastes in herbivores.

His partner switched menus even more dramatically, moving to a diet of browsers (giraffe, kudu and the like) and humans. By winter, a third of his food came from freshly killed humans. This was the animal that caused the lion's share of deaths among the railway workers, and Yeake estimates that he ate around 24, giving a total kill count of 35. Of course, these are only estimates, but there's a 95% chance that the true figure falls within the range of 4-72.

These disparate diets make the cooperation between the two males even more astounding. Both specialised on different rare prey and, if anything, their tastes diverged even further from one another over time. And yet, they frequently exposed themselves to danger to kill animals that only one ate. That sort of behaviour had never been seen before or since. Perhaps by working together, they could scatter both humans and game, so that both could be fed? For the moment, we just don't know.

Nor is it clear why the lions starting eating people in the first place, although Yeake has two theories. For a start, the lion that killed the most people had severe injuries, including diseases of the skull and teeth, skull evinced craniodental, poorly aligned jaws and a fractured tooth. It wasn't exactly a king among beasts, and it supports the idea that big cats are more likely to prey on humans if they're ill or impaired.

The Tsavo killings took place against a backdrop of intense environmental changes. Elephant populations had plummeted and as a result, woodlands were expanding and the savannah's grazers were being driven away. The remaining herds were thinned by a 13-year drought and a pair of viral epidemics in 1889 and 1898. And just as these walking sirloins dwindled away and the lions started to hunger, a new type of prey arrived in the region - humans, charged with building the Uganda Railway. The rest is history.

The two lions, Lieutenant Patterson (in top-left) and a Taita ancestral shrine.

Reference: PNAS: doi:10.1073/pnas.0905309106

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South African wildlife - Elephant encounter

Sun, 01 Nov 2009 09:40:36 -0500

We had numerous elephant sightings on our South Africa trip including a few family groups and a couple of lone males. Seeing them in documentaries or in zoos never quite captures just how big and impressive they are in the flesh, especially when they do things like beat up a tree. Note how this male uses his tusks and trunks to break off branches.

Also note how quiet it is except for the breaking of branches. Elephants may look like lumbering beasts, but their footfalls are dainty and quiet. They are 'digitigrade', meaning that they walk on their toes like a cat or a dog. Their heels rest on a spongy cushion that gives their foot its flat, round appearance - they've essentially got the world's largest platform shoes. And that means that walking elephants make precious little noise. You could watch a group disappear behind a bush about 10 metres away and have absolutely no idea that they were there.

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Drought drives toads to mate with other species

Sat, 31 Oct 2009 12:00:02 -0500

This article is reposted from the old Wordpress incarnation of Not Exactly Rocket Science.

When it comes to sex, it makes sense to stick to your own species. Even putting aside our own innate revulsion, inter-species liaisons are a bad idea because they mostly fail to produce any young. In the few instances they do, the hybrid progeny aren't exactly racing ahead in the survival stakes and are often sterile (think mules).

But having poor unfit young is still better than having no young at all and if an animal's options are limited, siring a generation of hybrids may be a last resort. Karin Pfennig from the University of North Carolina found that the plains spadefoot toad uses just this strategy in times of need.

Female toads breed just once a year, so it pays for them to make the right choice. According to Pfennig's work, they take their health and their environment into account when choosing mates. If their bodies are weak and their surroundings are precarious, the benefits that another species' genes can provide to their young are enough to outweigh the risks.

The south-western United States is home to two species of spadefoot toads with overlapping ranges - the Mexican spadefoot, Spea multiplicata and the Plains spadefoot, Spea bombifrons (more Kermit-like, according to Pfennig). Where both species mingle, they can breed and, as usual, the hybrid young are worse at spawning the next generation than their pure-blooded peers. Hybrid males are often sterile, and hybrid females lay fewer eggs.

Nonetheless, up to 40% of toads in certain areas can be hybrids and this intrigued Pfennig. She wanted to work out whether this was just incidental, or if some circumstances nudged the toads towards mating with individuals from a different species.

Their breeding grounds provided the answer; spadefoots lay eggs in temporary ponds and it's often a race for tadpoles to turn into frogs before the water dries out. Pfennig noticed that hybrids were more common in shallower ponds that dry out quicker, and that's because the two toad species develop at different rates.

On average, Mexican spadefoot tadpoles take less time to make the transition into frog-hood than Plains spadefoot ones, and hybrid tadpoles lie somewhere in the middle. This means that a Plains spadefoot female that's faced with a short-lived pond might do better if she mates with a Mexican spadefoot male, for her young will be more likely to grow up in time.

Pfennig tested this idea by placing Plains spadefoot females in tanks simulating shallow and deep ponds and letting them choose between recorded calls from males of both species. In deep water, they favoured their own kind about 65% of the time, but in the shallower pools, they had no such preferences.

In contrast, Mexican spadefoot females also showed no willingness for breed with other species. Since their tadpoles develop quickly anyway, they gain nothing by courting Plains spadefoot males. Pfennig also found that only Plains spadefoot females that lived in the same areas as Mexican spadefoots had the ability to switch their mate preferences. In parts of the States where the two species are geographically segregated, females never made this choice.

A Plains spadefoot female's health also affects which species she fancies. If she is fitter, she could provision her eggs with more nutrients and her tadpoles would grow faster. That would obviate her reliance on Mexican spadefoot males, even in shallower ponds.

Pfennig's experiments confirmed her idea; the unhealthiest females were the most likely to switch their preferences, from mating with their own kind in deep ones to preferring the other species in shallow ones.

Biologists are used to viewing a female's choice of partners solely in terms of the physical traits of males. But Pfennig's results show that it isn't just about which male has the flashiest colours, the most melodious song or the most impressive antlers. For females, mate choice is a much subtler affair, influenced by environment, personal health and probably many other factors that we have only begun to consider.

Reference: Pfennig. 2007. Facultative mate choice drives adaptive hybridization. Science 318: 965-7.

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Big-headed tiger snakes support long-neglected theory of genetic assimilation

Fri, 30 Oct 2009 09:34:36 -0500

Tiger snakes are a group of extremely venomous serpents found all over the southern half of Australia, and on many of its islands. Some were cut off from the mainland by rising sea levels more than 9,000 years ago, while others were inadvertently introduced by travelling humans and have been around for less than 30 years.

When the snakes first arrive on an island, they find prey that are generally larger than they're used to on the mainland. That puts them under strong evolutionary pressure to have larger heads, in order to swallow larger meals. But by feeding snakes from different populations with prey of varying sizes, Fabien Aubret and Richard Shine have found that the more recent immigrants solve the need for larger heads in a very different way than the long-term residents.

Young populations do it by being flexible. If growing tiger snakes from newly colonised islands are fed on large prey, their heads rapidly enlarge to cope with the sizeable morsels. This flexibility is an example of "phenotypic plasticity" and it doesn't involve any genetic changes.

But Aubret and Shine found that older populations lack this flexibility - they have larger heads from birth and the size of the prey they eat doesn't affect the way they grow. These adaptations are fixed in their genomes. In the heads of tiger snakes, Aubret and Shine have found evidence for a 67-year-old concept in evolution called "genetic assimilation", which has very rarely been tested and is often neglected.

Its name might conjure up images of science-fiction and DNA-stealing aliens, but genetic assimilation simply describes a means of adaptation. It was proposed in 1942 by Conrad Waddington, who suggested that species initially cope with fresh environments by being flexible - through plasticity. All species have a certain amount of variation built in to their developmental program, which they can exploit according to the challenges they face. In this case, the tiger snakes can grow larger heads if they encounter bigger meals.

But as populations face constant evolutionary pressures, natural selection eventually favours genes that produce the same results, the ones that plasticity once achieved. This is the crux of Waddington's theory - in time, natural selection eliminates plasticity by fixing genes for the same traits. Such genes as said to be "canalised".

Back in the 1950s, Waddington demonstrated this using fruit flies. He exposed developing flies to ether vapour and found that some developed a second thorax (the middle segment between the head and abdomen). By anyone's standards, that's a radical change, but one that was triggered by an unusual environment. Over time, Waddington selectively bred the double-thorax individuals and exposed each new generation to ether. After 20 rounds of this, he found that some flies developed a second thorax naturally, without being exposed to ether. The double-thorax trait, which was initially induced by the environment, eventually became governed by the fly's own genes.

It was a neat idea, but finding other natural examples has been very tricky. Aubret and Shine thinks that genetic assimilation tends to happen over such short timescales (geologically speaking) that you can only really detect it under unusual circumstances. And the spread of tiger snakes across Australia certainly fits that bill.

Aubret and Shine's experiments show that snakes from newly colonised areas had the greatest degree of plasticity when it comes to head size while those from the longest-colonised islands had the least. These differences become abundantly clear when you compare snakes from three populations.

Tiger snakes have only been on Trefoil Island for 30-40 years and the jaws of their hatchlings are still small. However, they're also plastic - if they eat big meals, they'll grow bigger. On Carnac Island, tiger snakes have been around for 90 years and there, the hatchlings have moderately sized jaws and a relatively high degree of plasticity. On Williams Island, the tiger snakes have been cut off from the mainland for 9,100 years and their jaws are not only large from birth but their growth has very little plasticity.

The differences between the Trefoil and Carnac serpents are particularly interesting, because they suggest that the process of genetic assimilation can take place over a very short span of time, as others have predicted. It starts manifesting within just a few decades, even in animals like tiger snakes that only breed after their second or third birthday. This rapid pace could explain why it's very difficult to observe this process in the wild.

Reference: Current Biology 10.1016/j.cub.2009.09.061

Images: Tiger snake by Ian Fieggan

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Venomous shrews and lizards evolved toxic proteins in the same way

Thu, 29 Oct 2009 12:00:34 -0500

The Northern short-tailed shrew is a small, energetic mammal that lives in central and eastern North America. The Mexican beaded lizard is a much larger reptile found in Mexico and Guatemala. These species are separated by a lot of a land and several million years of evolution, yet they share astonishing similarities. Not only are they both venomous, but the toxic proteins in their saliva have evolved in very similar ways from a common ancestor, converging on parallel lethal structures independently of one other.

This discovery, from Yael Aminetzach at Harvard University, shows that adaptations are sometimes very predictable. Despite the many changes that could have shaped the course of venom proteins in lizards and shrews, they seem to have gone down a consistent and similar route.

Northern short-tailed shrew by Giles Gonthier; Mexican beaded lizard by PiccoloNamek

The northern short-tailed shrew is one of the few venomous mammals, but its poisonous bite is painful to humans and can kill smaller animals. The key to its venom is a protein called BLTX, whose job is to cut another protein in two. This chemical reaction frees a molecule called bradykinin, which widens blood vessels and lowers blood pressure. It's a necessary job, but BLTX is so active that if floods the body with bradykinin - an overdose that leads to paralysis and death.

BLTX is a dark, hyperactive descendant of an ancestral protein called kallikrein-1, which does the same thing but in a much more restrained way. Aminetzach found that BLTX is a longer version of kallikrein and the extra amino acids it has gained have changed the structure of the protein's 'active site'.

The active site is the protein's business end - it allows BLTX to latch onto the right targets and catalyse the relevant chemical reactions. It's also the part of the protein that has changed the most from the harmless kallikrein model; amino acids around BLTX's active site have changed about twice as much as the rest of the protein. As a result, the site is larger, more flexible and better at drawing in its target, and the protein as a whole has become hyperactive.

And amazingly, the Mexican beaded lizard has gone through similar changes. Its venom relies on a protein called GTX, which is also descended from kallikrein. Like BLTX, it too is a longer version of its ancestor, and while its extra amino acids have been shoved into different places, the results are the same. The changes have altered the protein's active site so that it's larger, more flexible and better at drawing in its target.

These changes are very specific to these toxic proteins. By studying 24 relatives of kallikrein, Aminetzach found that none of the non-toxic members of the family have any of the changes that BLTX and GTX share.

This study demonstrates that evolution doesn't work with infinite possibilities. Often, there are only a few roads leading to the same destination. Through different amino acid changes, both BLTX and GTX have evolved similar structures and have turned into weapons. This predictability of venom evolution may be useful to us - for example, Aminetzach suggests that it could allow scientists to more easily identify toxins from others species, even distantly related ones.

Reference: Current Biology 10.1016/j.cub.2009.09.022

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Holy fellatio, Batman! Fruit bats use oral sex to prolong actual sex

Tue, 27 Oct 2009 19:56:26 -0500

Many humans whinge about not getting oral sex often enough, but for most animals, it's completely non-existent. In fact, we know of only animal apart from humans to regularly engage in fellatio - the short-nosed fruit bat (Cynopterus sphinx).

The bat's sexual antics have only just been recorded by Min Tan of China's Guangdong Entomological Institute (who are either branching out, or are confused about entomology). Tan captured 60 wild bats from a nearby park, housed them in pairs of the opposite sex and voyeuristically filmed their liaisons using a night-time camera. Twenty of the bats got busy, and their exploits were all caught on video.

Male bats create tents by biting leaves until they fall into shape. These provide shelter and double as harems, each housing several females who the male mates with. Fruit bat sex goes like this: the female approaches and sniffs the male, and both partners start to lick one another. The male makes approaches with his thumbs (like the Fonz) and mounts the female (like the Fonz). Sex itself is the typical rhythmic thrusting that we're used to, and afterwards, the male licks his own penis for several seconds.

But Tan also found that female bat will often bend down to lick the shaft of her mate's penis during sex itself. This behaviour happened on 70% of the videos, making it the only known example of regular fellatio in a non-human animal. It also prolonged the sexual encounter - males never withdrew their penises when they were being licked and, on average, the behaviour bought the couple an extra 100 seconds of sex over and above the usual 2 minutes. The licking itself only lasted for 20 seconds on average, so each second of it buys six extra seconds of penetration.

NSFW - short-nosed fruit bats having sex. I will have you know that the music choice came with the video and has nothing to do with me.

Oral sex is rare in other animals. Bonobos do it (but really, what don't they do?) but it's more of a form of play among young males, and there's one anecdotal instance of an orang-utan doing the same. Some animals, such as ring-tailed lemurs, lick each other's genitals to judge whether they're ready for mating, but there's no evidence that they do so as an actual part of sex. As for other bats, it's entirely possible that they too engage in oral sex. However, given their inaccessible roosts and nocturnal habits, we're largely in their dark about their sex lives.

Nonetheless, Tan suggests a few possible reasons for the short-nosed fruit bat's penchant for fellatio, aside from the anthropocentric conclusion of 'pleasure-giving'. Bat penises contain erectile tissue much like our own. It gets stiffer if it's stimulated, so females could use oral sex to prolong their encounters with males, by maintain their erections or lubricating it for easier entry.

While many of us might nod sagely at the need for longer sex, Tan suggests that for the bats, it could mean easier transport of sperm to the oviduct, or more secretions from the female that are conducive to fertilisation. It could also be a way of hogging a mate, keeping him away from rival females.

Alternatively, the antiseptic properties of saliva might help to strip the male's penis of bacteria or fungi, and prevent the spread of sexually transmitted diseases. The fact that males lick their own penises after sex supports this idea.

And finally, oral sex might help females to pick up chemical traces on her mate that might suggest if he's a suitable mate. Obviously, they'd already be having sex, but female mammals often exert choice over their sexual partners after the fact, rejecting sperm from inferior males, or encouraging congress with superior ones to displace it. All of these explanations are just hypotheses for the moment, but they could all be tested in the future.

Reference: Tan, M., Jones, G., Zhu, G., Ye, J., Hong, T., Zhou, S., Zhang, S., & Zhang, L. (2009). Fellatio by Fruit Bats Prolongs Copulation Time PLoS ONE, 4 (10) DOI: 10.1371/journal.pone.0007595

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Drinking blood makes vampire spider sexier

Tue, 27 Oct 2009 08:30:32 -0500

In East Africa lives a species of spider that drinks mammalian blood. But fear not - Evarcha culicivora is an indirect vampire - it sates its thirst by preying on female mosquitoes that have previously fed on blood themselves.

Even though its habitat is full of non-biting midges called "lake flies", it can tell the difference between these insects and the blood-carrying mozzies it carries. Robert Jackson from the University of Canterbury discovered this behaviour a few years ago and one of his colleagues, Fiona Cross, has now found that the blood isn't just a meal for the spiders, it's an aphrodisiac too.

Photo of E.culicivora eating a mosquito, by R. Jackson.

Cross made spiders choose between two adults of the opposite sex, by wafting their smells down a tube on different days and seeing which drew the choosy spider's attention for the longest time. The contenders had been fed on one of four diets: blood-fed female mosquitoes, sugar-fed female mosquitoes, male mosquitoes, or lake flies.

She found that only a menu of blood-fed mosquitoes made spiders more attractive to the opposite sex, and both males and females shared this turn-on. If spiders were switched from a diet of lake flies to one of bloody mosquitoes, their scents became more attractive. Even a single meal of blood makes the spiders smell more attractive. Likewise, fasting, or moving from mozzies to lake flies even for just a day, curtails the sex appeal of an individual's odour.

So for E.culicivora to maintain its sensuous scent, it needs to continuously feed on blood. In this way, spiders that smell of blood are probably those that are best at catching mosquitoes, and potential partners may be using the odours as a way of sussing out the quality of their mates. Of course, that's just a hypothesis. Next, Cross plans to see if spiders on a blood diet actually mate more often, or produce more viable eggs and sperm.

The other alternative is that spiders are using the smell of blood to lure in potential mates, by tricking them into thinking that prey is near. But Cross thinks this is unlikely - spiders were only drawn to the smell of blood if it was given off by individuals of the opposite sex.

The importance of smell might come as a surprise, especially since E.culicivora is a jumping spider, a group that's better known for their keen eyesight. But when it comes to mating, previous studies show that smell plays an equally important role in identifying a partner. If the smell was simply making them hungry, the gender of its source wouldn't matter.

Perhaps the actual chemical lure is produced after blood is processed in the spider's body. Perhaps it's a combination of blood and a sex-specific chemical that piques a partner's interest. The only real way to find out is to work out the precise chemicals that E.culicivora finds so appealing, and that's next on Cross's to-do list.

In the mean time, there are probably many other examples in nature of animals to rely on the same smells in courtship rituals as in other aspects of their lives. For examples, noctuid moths use sex pheromones that mimic smelly chemicals given off by plants, the same chemicals that they track to find somewhere to lay their eggs. And the European starling adds aromatic plants into its nest to attract females.

Reference: PNAS doi:10.1073/pnas.0904125106

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How humans started a bacterial pandemic in chickens

Mon, 26 Oct 2009 18:13:14 -0500

The prospect of infections spreading from animals to humans has become all too real with the onset of the current swine flu pandemic, and the threat of a bird flu still looming. But infections can jump the other way too. Decades before the world's media were gripped with panic over bird flu, humans transferred a disease to chickens and it has since caused a poultry pandemic right under our noses.

The infection in question is a familiar one - Staphylococcus aureus, a common human bacterium that's behind everything from mild skin infections to life-threatening MRSA. It causes chicken diseases too, including septic arthritis and 'bumblefoot'. But in the 1970s, broiler chickens began developing a new type of S.aureus infection called 'bacterial chrondronecrosis with osteomyelitis' or, more simply, BCO. It's a bone infection and it's a major cause of lameness in broiler chickens.

This new disease had human origins. Bethan Lowder from the University of Edinburgh has shown that all of the bacteria behind BCO share a common ancestor, which jumped from humans to chickens in Poland, around 38 years ago. From that point on, the bacterium's travel itinerary was set. Just as air travel has facilitated the spread of swine flu among humans, a global distribution network for chickens made it easy for S.aureus to spread all over the world aboard its new feathery hosts.

Lowder traced the common ancestry of S.aureus in chickens by analysing the genes of 57 samples. Of these, 48 came from healthy and diseased chickens across eight countries and four continents, and 9 were taken from different species of wild and domesticated birds. Amazingly, she found that two-thirds of all the broiler chicken samples came from a single strain of the bacterium called ST5.

ST5 infects humans all over the world and is one of the most successful strains of S.aureus to do so. But Lowder found that all of the chicken samples were more closely related to each other than they were to any of the human bacteria from the same strain. They all shared a common ancestor - a lineage of ST5 found only in Poland. Around 38 years ago, this pioneering bacterium made the leap from humans to chickens and its descendants have spread from Poland to countries as far as the US and Japan.

Since then, the ST5 strain has adapted to its new host. It has lost many of the genes it needs to cause disease in humans but it has picked up others that allow it to better infect chickens. A complete sequence of the bacterium's genome reveals that since its human days, it has picked up five new genes from other bird sources, none of which are found in humans or other mammals. In fact, Lowder thinks that the ST5 strain may be particularly good at picking up mobile genes from other sources. That might explain why both human and chicken versions are so successful, and why the human one often picks up genes that allow it to shrug off powerful antibiotics.

It's not clear how exactly these changes benefit the bacteria, but certainly, they're much better at resisting a chicken's immune system than their human predecessors. When faced with chicken heterophils - a type of white blood cell - the poultry strains were much more likely to survive than the human equivalents.

Lowder thinks that globalisation was the key to the new pandemic. In just the last fifty years, the broiler chicken industry has shifted from one dominated by small farms to a multi-billion dollar leviathan controlled by a small number of multinationals. These companies transport a relatively few breeding lines of chickens all over the world, and the low genetic diversity of these birds makes them vulnerable to infections as opportunistic as S.aureus.

She recommends that livestock are screened regularly so that emerging diseases can be picked up, and that stocks should often be cleansed of S.aureus, to nip potential new threats in the bud. Better regulations for international transport wouldn't go amiss either - it's no surprise that Australia, a country with stringent regulations on importing livestock, has no trace of the pandemic S.aureus strain.

Reference: PNAS: 10.1073/pnas.0909285106

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Mantis shrimp eyes outclass DVD players, inspire new technology

Sun, 25 Oct 2009 14:00:39 -0500

The most incredible eyes in the animal world can be found under the sea, on the head of the mantis shrimps. Each eye can move independently and can focus on object with three different areas, giving the mantis shrimp "trinocular vision". While we see in three colours, they see in twelve, and they can tune individual light-sensitive cells depending on local light levels. They can even see a special type of light - 'circularly polarised light' - that no other animal can.

But Nicholas Roberts from the University of Bristol has found a new twist to the mantis shrimp's eye. It contains a technology that's very similar to that found in CD and DVD players, but it completely outclasses our man-made efforts. If this biological design can be synthesised, it could form the basis of tomorrow's multimedia players and hard drives.

Previous studies have found that mantis shrimps can detect polarised light - light that vibrates in a single plane as it travels. Think of attaching a piece of string to a wall and shaking it up and down, and you'll get the idea. Last year, scientists discovered that they can also see circularly polarised light, which travels in the shape of a helix. To date, they are still the only animal that can see these spiralling beams of light.

Its secret lies at a microscopic level. Each eye is packed with light-sensitive cells called rhabdoms that are arranged in groups of eight. Seven sit in a cylinder and each has a tiny slit that polarised light can pass through if it's vibrating in the right plane. The eighth cell sits on top and its slit is angled at 45 degrees to the seven below it. It's this cell that converts circularly polarised light into its linear version.

In technical terms, the eighth cell is a "quarter-wave plate", because it rotates the plane in which light vibrates. Similar devices are also found in camera filters, CD players and DVD players but these man-made versions are far inferior to the mantis shrimp's biological tech.

Synthetic wave plates only work well for one colour of light. If you change the wavelength slightly, they become ineffective, so designing a wave plate that works for many colours is exceptionally difficult. But the mantis shrimp has already done it. Its eyes work across the entire visible spectrum, from ultraviolet to infrared, achieving a level of performance that our technology can't compete with.

What's more, the same eighth cell not only manipulates circularly polarised light, but it can sense ultraviolet light too. It's a detector and a converter - a two-for-one deal that nothing man-made shares.

Why the mantis shrimp needs such a sophisticated eye is unclear. It could help them to see their prey more clearly in water, which is rife with circularly polarised reflections. It needs good eyesight to be able to hit its prey accurately. Like a crustacean Thor, mantis shrimps shatter their victims with devastating hammer blows inflicted by the fastest arms on the planet. Their forearms, which end in clubs or spears, can travel through water at 10,000 times the acceleration of gravity and hit with the force of a rifle bullet.

Another option is that their super-eyes allow them to send and receive secret messages. A mantis shrimp's shell reflects circularly polarised light, and males and females produce these reflections from different body parts. Their ability to see this type of light could give them a hidden channel of communication that only they can see, for use in courtship or combat.

Whatever the reason for it, Roberts thinks that the eye's structure is "beautifully simple". It's all in the shapes of the cells, their size, and the amount of fat in their membranes. For all its outstanding performance, the eye's abilities were probably easy to evolve, requiring only small tweaks to the basic blueprint of the light-detecting cells.

Now that we know about the microscopic structures behind the mantis shrimp's amazing eye, Roberts is hopeful that engineers can mimic it using liquid crystals. "The cool thing is I think it's actually something you could make and it would improve the workings of current technologies such as Blu-Ray, which uses multiple wavelengths of light, and of future data storage devices," he said. It wouldn't be the first time that crustaceans have inspired technology. A new type of X-ray telescope, for example, was based on the eye of the lobster.

Reference: Nature Photonics DOI: 10.1038/NPHOTON.2009.189

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