Research Blogging - Mathematics - English

Let the Buyer Beware

2012-05-22T13:26:00Z

"Modern societies are complex systems" may be the understatement of the year. Obvious or not, however, it must be stated when attempting to model even some minuscule aspect of such a society. Take, for instance......

Tiago P. Peixoto, & Stefan Bornholdt. (2012) No Need for Conspiracy: Self-Organized Cartel Formation in a Modified Trust Game. Physical Review Letters, 108(21), 218702. info:/10.1103/PhysRevLett.108.218702

Does Social Status Change Brains?

2012-05-16T12:33:15Z

Photo by The Grappling Source Inc. at Wikimedia CommonsBeing subordinated is stressful. The process of one individual lowering the social rank of another often involves physical aggression, aggressive displays, and exclusion. In addition to the obvious possible costs of being subordinated (like getting beat up), subordinated individuals often undergo physiological changes to their hormonal systems and brains. Sounds pretty scary, doesn’t it? But what if some of those changes are beneficial in some ways?Dominance hierarchies are a fact of life across the animal kingdom. In a social group, everyone can’t be dominant (otherwise, life would always be like an episode of Celebrity Apprentice, and what could possibly be more stressful than that?). Living in a social group is more peaceful and nutritive when a clear dominance hierarchy is established. Establishing that hierarchy often involves a relatively short aggressive phase of jostling for position, followed by a longer more stable phase once everyone knows where they fall in the social group. Established dominance hierarchies are not always stable (they can change over time or from moment to moment) and they are not always linear (for example, Ben can be dominant over Chris, who is dominant over David, who is dominant over Ben). But they do generally help reduce conflict and the risk of physical injury overall.Nonetheless, it can be stressful to be on the subordinate end of a dominance hierarchy and these social interactions are known to cause physiological changes. Researchers Christina Sørensen and Göran Nilsson from the University of Oslo, Cliff Summers from the University of South Dakota and Øyvind Øverli from the Norwegian University of Life Sciences investigated some of these physiological differences among isolated, dominant, and subordinate rainbow trout.A photo of a rainbow trout by Ken Hammond at the USDA. Photo at Wikimedia Commons.Like other salmonid fish, rainbow trout are aggressive, territorial and develop social hierarchies as juveniles. Dominant trout tend to initiate most of the aggressive acts, hog food resources, grow larger, and reproduce the most, whereas subordinate trout display less aggression, feeding, growth, and reproduction. The researchers recorded the behavior, feeding and growth rates in three groups of fish: trout housed alone, trout housed with a more subordinate trout, and trout housed with a more dominant trout. The researchers also measured cortisol (a hormone involved in stress responses), serotonin (a neurotransmitter involved in mood, the perception of food availability, and the perception of social rank, among other things) and the development of new neurons (called neurogenesis) in these same fish.This video of two juvenile rainbow trout was taken by Dr. Erik Höglund. Here is Christina Sørensen’s description of the video: “What you see in the film is two juvenile rainbow trout who have been housed on each side of a dividing wall in a small aquarium. The dividing wall has been removed (for the first time) immediately before filming. You will see that the fish initially show interest for each other, followed by a typical display behaviour, where they circle each other. Finally one of the fish will initiate aggression by biting the other. First the aggression is bidirectional, as they fight for dominance, but after a while, one of the fish withdraws from further aggression and shows only submissive behaviour (escaping from the dominant and in the long run trying to hide... and as is described in the paper, depressed feed intake). The video has been cut to show in quick succession these four stages of development of the dominance hierarchy”. The researchers found that as expected, the dominant trout were aggressive when a pair was first placed together, but the aggression subsided after about 3 days. Also as expected, the dominant and isolated trout were bold feeders with low cortisol levels and high growth rates, whereas the subordinate trout did not feed as well, had high cortisol levels and low growth rates. Additionally, the subordinate trout had higher serotonin activity levels and less neurogenesis than the dominant or isolated trout. These results suggest that the subordination experience causes significant changes to trout brain development (Although we can’t rule out the possibility that fish with more serotonin and less neurogenesis are predisposed to be subordinate). In either case, this sounds like bad news for subordinate brains, right? Maybe it is. Or maybe the decrease in neurogenesis just reflects the decrease in overall growth rates (smaller bodies need smaller brains). Or maybe something about the development of these subordinate brains improves the chances that these individuals will survive and reproduce in their subordination. A crayfish raising its claws. Image by Duloup at Wikimedia.Research on dominance in crayfish by Fadi Issa, Joanne Drummond, and Don Edwards at...

Sørensen, C., Nilsson, G., Summers, C., & Øverli, �. (2012) Social stress reduces forebrain cell proliferation in rainbow trout (Oncorhynchus mykiss). Behavioural Brain Research, 227(2), 311-318. DOI: 10.1016/j.bbr.2011.01.041

Issa, F., Drummond, J., Cattaert, D., & Edwards, D. (2012) Neural Circuit Reconfiguration by Social Status. Journal of Neuroscience, 32(16), 5638-5645. DOI: 10.1523/JNEUROSCI.5668-11.2012

Yeh, S., Fricke, R., & Edwards, D. (1996) The Effect of Social Experience on Serotonergic Modulation of the Escape Circuit of Crayfish. Science, 271(5247), 366-369. DOI: 10.1126/science.271.5247.366

Issa, F., & Edwards, D. (2006) Ritualized Submission and the Reduction of Aggression in an Invertebrate. Current Biology, 16(22), 2217-2221. DOI: 10.1016/j.cub.2006.08.065

Flat tori in 3D

2012-05-11T08:20:08Z

It's been a while since I've read a pure math paper, but when I saw the picture I knew I had to pick this one up. For the pure mathematicians out there: I haven't done pure math since my grad years, so feel free to pitch in and correct me if I misunderstood any of the following! "Torus" is mathematics for donut. Take a very flexible square -- imagine it's made of rubber -- roll it, then glue together the circles at the two ends. Congratulations. You've made a torus. Now suppose you live on the torus and you need a map that takes you from A to B. Think of an atlas that shows you all the streets and cities on the torus. How do you map the torus onto a flat surface so that you can actually hold the map in your hands? Well, you go back to that square you used to make the torus, right? Cut out the donut vertically, then horizontally, and you've got your square back and now you can map all the streets you want. Problem: the distances on your map will now be distorted, just like continent sizes are distorted on world maps (have you ever seen this image?). Well, it turns out, there's a famous theorem, the Nash embedding theorem, that states that any Riemannian manifold (replace that with the torus we were talking about) can be isometrically embedded into the Euclidean space. Isometrically here means in such a way that it preserves the distances. So the square won't work for the torus (it does not preserve distances), but there is a way to get a map with such property. Problem: how to visualize it? See, that's always been my issue with math. It's so beautiful at telling you what exists and what doesn't, but then you get to the practical side, as in, "Okay, now give me such map," and the mathematician shrugs and looks at you all weird: "I told you it exists, aren't you happy with that?" Sorry, I'm joking, let's get serious again. Here's the news: we now have a visualization of a flat torus (the isometric map) in the three-dimensional space. In the latest issue of PNAS, Vincent Borrellia, Said Jabranea, Francis Lazarusb, and Boris Thibert present an isometric embedding of the flat torus in three-dimensional space. Forget the jargon and just look at the picture: how cool is that? And here is the best part: see all those corrugation in the figure? It's because it's a "smooth" fractal surface, a sort of hybrid between a fractal and smooth surface. The embedding is "a continuously differentiable map that cannot be enhanced to be twice continuously differentiable. As a consequence, the image surface is smooth enough to have a tangent plane everywhere, but not sufficient to admit extrinsic curvatures." Yes. I'm still a mathematician at heart, because I read this and got all excited. Of course, the rest of the paper went right past my head, but any of you willing to add a few more insights, you are more than welcome to do so in the comments below. Thanks! A few more details on the paper here. Borrelli, V., Jabrane, S., Lazarus, F., & Thibert, B. (2012). From the Cover: Flat tori in three-dimensional space and convex integration Proceedings of the National Academy of Sciences, 109 (19), 7218-7223 DOI: 10.1073/pnas.1118478109...

Borrelli, V., Jabrane, S., Lazarus, F., & Thibert, B. (2012) From the Cover: Flat tori in three-dimensional space and convex integration. Proceedings of the National Academy of Sciences, 109(19), 7218-7223. DOI: 10.1073/pnas.1118478109

Spurious Positive Mapping of the Brain?

2012-05-02T13:32:34Z

Many fMRI studies could be giving false-positive results according to an important new paper from Anders Eklund and colleagues: Does parametric fMRI analysis with SPM yield valid results?—An empirical study of 1484 rest datasets.The authors examined the SPM8 software package, probably the most popular tool for analyzing neuroimaging data.Their approach was beautifully simple. They wanted to check how often conventional analysis of fMRI would "find" a signal when there wasn't really anything happening. So they took data from nearly 1,500 people who were scanned when they were just resting, and saw what would happen if you looked for "task related" activations in those scans, even though there was in fact no task. It's a very clever use of the resting state data.Eklund et al ran the analysis many thousands of times, under various different conditions. This is the key finding:This shows the proportion of analyses which produced significant "activations" associated with various different "tasks". In theory, the false positive rate should be way down at the bottom at 5% in each case. That's the error rate they told SPM8 to provide. As you can see, it was often much higher. Oh dear.The error rate depended on two main things. Most important was the task design. Block designs were much worse than event-related designs (see the labels at the bottom: B1,2,3,4 are block, E1,2,3,4 are event.) The longer the blocks, the more errors. B4, the most error-ridden design of all, corresponds to 30 second blocks.That's bad news because that's a very common design.Secondly, the repeat time (TR) mattered, especially for block designs. The TR is how long it takes to scan the whole brain once. The longer the TR, the better, the data showed: 1 second TRs are really dodgy. Luckily, they are rarely used. 2 seconds is OK for most event-related designs, but block designs really suffer. 3 seconds is even better.Because most fMRI studies today use 2-3 second TRs, this is somewhat reassuring, but for block design B4 the error rate was still up to 30% even with TR=3. Oh dear, oh dear.So what went wrong? It's complicated, and you should read the paper, but in a nutshell the problem is that fMRI data analysis assumes that there are only two sources of data: the real brain activation signal, and white noise. The key assumption is that it's white noise, which essentially means that it is random at any moment in time: knowing about what the noise did in the past tells you nothing about what it will do in the future. "Random" noise that's actually correlated with itself over time is not white noise.Now noise in the brain is certainly not white, for various reasons, including the effects of breathing and heart rate (which of course are cyclical, not random.) All fMRI analysis packages try to correct for this - but Eklund et al have shown that SPM8's approach doesn't manage to do that, at least for many designs.What about rival fMRI software like FSL or BrainVoyager? We don't know. They use different approaches to noise modelling, which might mean they do better, but maybe not.And the really big question: does this mean we can't trust published SPM8 results? Does SPM stand for Spurious Positive Mapping? Well, that's also not clear. All of Eklund et al's analyses were based on single subject data. But most fMRI studies pool the results from more like 20 or 30 subjects. Averaging over many subjects might make the false positives cancel out, but we don't yet know if that would solve the problem or only lessen it.Eklund, A., Andersson, M., Josephson, C., Johannesson, M., and Knutsson, H. (2012). Does parametric fMRI analysis with SPM yield valid results?—An empirical study of 1484 rest datasets NeuroImage DOI: 10.1016/j.neuroimage.2012.03.093...

Eklund, A., Andersson, M., Josephson, C., Johannesson, M., & Knutsson, H. (2012) Does parametric fMRI analysis with SPM yield valid results?—An empirical study of 1484 rest datasets. NeuroImage. DOI: 10.1016/j.neuroimage.2012.03.093

Why This Horde of Idiots is No Genius

2012-05-02T12:53:14Z

At first look (in Part 1 of this post), swarm theory seems to predict that the larger the social group, the better the resulting group decisions and behaviors. Then, with over 300 million of us in the U.S., shouldn’t we only be making brilliant decisions? And with over 7 billion worldwide, shouldn’t we have already prevented all international conflicts, cancer, and environmental destruction? And why the heck is Snooki still everywhere we look?! A riot in Vancouver, Canada after the Vancouver Canucks lost the Stanley Cup in 2011 left the city with scars. Photo by Elopde at Wikimedia Commons. Many large groups of people make incredibly stupid decisions. Like proverbial lemmings (a hoax perpetuated by Disney), large groups of people have caused incredible damage to their community after their hockey team lost the Stanley Cup, quit their jobs and given away all of their possessions believing the end of the world was coming on May 21, 2011 (ehem… we’re still here), and insisted that wearing baggy pants around the thighs is a reasonable thing to do even though it is not sexy and it trips you when you try to run. Where are we going wrong? Tom Seeley at Cornell University has gained tremendous insight into effective group decision-making from his years observing honeybees, which he shares with us in his book, Honeybee Democracy. (By the way, this is also one of the best books out there for painting a picture of the life of a behavioral biologist). Honeybees live in swarms of thousands. When the hive becomes overcrowded, about a third of the worker bees will stay home to rear a new queen while the old queen and the rest of the hive will leave to begin the process of finding a new home. During this time, the migrants will coalesce on a nearby branch while they search out and decide among new home options. This process can take anywhere from hours to days during which the colony is vulnerable and exposed. But they can’t be too hasty: choosing a new home that is too small or too exposed could be equally deadly. This homeless honeybee swarm found an unconventional "branch". They'd better decide on a new home before the cyclist gets back! Photo by Nino Barbieri at Wikimedia. Although each swarm has a queen, she plays no role in making this life-or-death decision. Rather, this decision is made by a consensus among 300-500 scout bees that results after an intense “dance-debate”. Then, as a single united swarm, they leave their branch and move into their new home. At this point, it’s critical that the swarm is unified in their choice of home site, because a split-decision runs the risk of creating a chaos in which the one and only queen can be lost and the entire hive will perish. This is a high-stakes decision that honeybees make democratically, efficiently, and amazingly, they almost always make the best possible choice! How do they do that? And how can we do that? Each dot represents where on the body this dancer was head-bumped by a dancer for a competing site. Each time she's bumped, she's a little less enthusiastic about her own dance. Figure from Seeley, et al. 2012 paper in Science.The honeybee house-hunting process has several features that allow them as a group to hone in on the best possible solution. The process begins when a scout discovers a site that has potential for a new home. She returns to her swarm and reports on this site, using a waggle dance that encodes the direction and distance to the site and her estimate of its quality. The longer she dances, the better she perceived the site to be. Other scouts do the same, perhaps visiting the same site or maybe a new one, and they report their findings in dance when they return. More scouts are recruited and the swarm breaks into a dancing frenzy, with many scouts dancing for multiple possible sites. Over time, scouts that are less enthusiastic about their discovered site stop dancing, in part discouraged by dancers for other sites that head-bump them while beeping. Eventually, the dancing scouts are unified in their dance for what is almost always the best site. The swarm warms up their flight muscles, and off they go, in unison to their new home.What can we learn from this process? Tom has summarized his wisdom gained from observing honeybees in the following: Tom Seeley’s Five Habits of Highly Effective Hives 1. “Group members share a goal”. This is easy for honeybees, but not as much for us. All of the honeybees in a swarm share the same goal: Find the best possible home as quickly as possible. People are not always similar in our goals, needs and wants and one person’s goals are sometimes in direct conflict with another person’s goals. The trick here is finding common ground. 2. “Group members search broadly to find possible solutions to the problem”. Seek out information from as many sources as you can. Be creative. Use your personal experience. And if the group is diverse, there will be a broader range of personal experience to harness. Diversity increases the ability of a group to make the best decisions. 3. “Group members contribute their information freely and honestly”. This requires a welcoming and supportive environment that withholds judgment of the individuals for the ideas expressed. You don’t have to agree with an idea to respect and listen to the person expressing it. 4. “Group members evaluate the options independently and they vote independently”. Just as scout bees don’t dance for a site they have not visited and assessed themselves, we should not advocate possible solutions or candidates that we have not ourselves looked into and thought critically about. A group can only be smarter than the individuals in it if the individuals think for themselves. 5. “Group members aggregate their votes fairly”. Everyone gets a vote and each one counts equally. ‘Nuff said. We can learn a lot from these honeybees. Even when the stakes are high, we can make good decisions for our group if we are open, honest, inclusive, fair and think independently. Want to know more? Check these out: 1....

Seeley, T., Visscher, P., Schlegel, T., Hogan, P., Franks, N., & Marshall, J. (2011) Stop Signals Provide Cross Inhibition in Collective Decision-Making by Honeybee Swarms. Science, 335(6064), 108-111. DOI: 10.1126/science.1210361

List, C., Elsholtz, C., & Seeley, T. (2009) Independence and interdependence in collective decision making: an agent-based model of nest-site choice by honeybee swarms. Philosophical Transactions of the Royal Society B: Biological Sciences, 364(1518), 755-762. DOI: 10.1098/rstb.2008.0277

Math Shows Today's Writers Are Less Influenced by the Past

2012-04-30T15:03:02Z

When Charles Dickens wrote It was the of, it was the of, the immortal first words in A Tale of Two Cities, he can't have imagined that 21st-century computer scientists would parse his prepositions and pronouns as part of vast literary data sets. But today's researchers are studying the unimportant words in books to find important literary trends. With the meaty words taken out, language becomes a numbers game. To see how literary styles evolve over time--a science dubbed "stylometry"--researchers led by James Hughes at Dartmouth College turned to Project Gutenberg. The site contains the full text of more than 38,000 out-of-copyright books. Researchers began their mining expedition by digging out every author who wrote after 1550, had a known date of birth and (when relevant) death, and had at least 5 English-language books digitized. These criteria gave the researchers a set of 537 authors with 7,733 published works. But they weren't interested in every word of those books. Nouns and adjectives were out: No Kareninas or Lolitas, nothing nice or bad or beautiful, no roads or homes or people. Most verbs were out, except for forms of the utilitarian to be. No one could speak or walk or Fly, good Fleance! It may seem that the researchers were stripping all the information-containing words out of the sentences, and in fact that was their goal: "Content-free" words were all they wanted. The 307-word vocabulary that remained from the books was mostly prepositions, conjunctions, and articles. This linguistic filler, the little stitches that hold together the good stuff, is known to contain a kind of authorial fingerprint. We may not think much about these words when we're writing or speaking, but scientists can use them to define our style. Hughes and his team used computer analysis to score each author's similarity to every other author. They found that before the late 18th century, authors's stylistic similarity didn't depend on how close to each other they lived. (Each author was represented by a single year, the midpoint between his or her birth and death.) During this time period, authors who lived in the same generation didn't influence each other's styles much more than authors who lived hundreds of years away. But from the late 18th century to today, it was a different story. Stylistically, authors were more similar to their contemporaries than to other writers. By the late 19th century, writers closely matched the style of other writers who lived at the same time (at least according to the computers tallying up their non-content words). This influence dropped off outside of 30 years. In other words, authors who lived more than three decades away each other may as well have lived centuries away, for all the similarity between their writing. Looking at more recent books, that window of influence seems to become even tighter. Among authors from the first half of the 20th century, the similarity of style drops off beyond just 23 years. Over time, authors have become more and more influenced by the other authors writing at the same time. The researchers say this may simply be due to the number of books published. In the early part of their dataset, there were few enough books around that a studious person could read, well, most of them. But as more and more books were published, contemporary books made up a larger share of what was available to read. Authors have filled more and more shelves in their libraries with books by their peers--and this has made them more likely to echo each other's styles. Because Project Gutenberg relies on public-domain material, there weren't very many authors after the mid-20th century included in this study. Looking forward, "You would expect a continued diminishing of influence," says Daniel Rockmore, the paper's senior author. Contemporary books take up an ever greater portion of what's available to read. In addition to the huge number of books published each year (more than 288,000 in the United States in 2009), there are now e-books and e-readers and Japanese Twitter novels. A century from now, we may be able to look back and see that today's authors had an ever-condensing frame of influence. Of course, by then literary styles might only last a week. Most books will be forgotten, but every author will be a revolutionary. James M. Hughes, Nicholas J. Foti, David C. Krakauer, & Daniel N. Rockmore (2012). Quantitative patterns of stylistic influence in the evolution of literature PNAS : 10.1073/pnas.1115407109 Image: Library of Congress from ep_jhu/Flickr...

James M. Hughes, Nicholas J. Foti, David C. Krakauer, & Daniel N. Rockmore. (2012) Quantitative patterns of stylistic influence in the evolution of literature. PNAS. info:/10.1073/pnas.1115407109

Can a Horde of Idiots be a Genius?

2012-04-25T11:54:31Z

Let’s face it: The typical individual is not that bright. Just check out these human specimens: Yet somehow, if you get enough numbskulls together, the group can make some pretty intelligent decisions. We’ve seen this in a wide variety of organisms facing a number of different challenges.In a brilliant series of studies, Jean-Louis Deneubourg, a professor at the Free University of Brussels, and his colleagues tested the abilities of Argentine ants (a common dark-brown ant species) to collectively solve foraging problems. In one of these studies, the ants were provided with a bridge that connected the nest to a food source. This bridge split and fused in two places (like eyeglass frames), but at each split one branch was shorter than the other, resulting in a single shortest-path and multiple longer paths. After a few minutes, explorers crossed the bridge (by a meandering path) and discovered the food. This recruited foragers, each of which chose randomly between the short and the long branch at each split. Then suddenly, the foragers all started to prefer the shortest route. How did they do that?This figure from the Goss et al 1989 paper in Naturwissemschaften shows (a) the design of a single module, (b) ants scattered on the bridge after 4 minutes (I promise they’re there), and (c) ants mostly on the shortest path after 8 minutesYou can think of it this way: a single individual often tries to make decisions based on the uncertain information available to it. But if you have a group of individuals, they will likely each have information that differs somewhat from the information of others in the group. If they each make a decision based on their own information alone, they will likely result in a number of poor decisions and a few good ones. But if they can each base their decisions on the accumulation of all of the information of the group, they stand a much better chance of making a good decision. The more information accumulated, the more likely they are to make the best possible decision. In the case of the Argentine ant, the accumulated information takes the form of pheromone trails. Argentine ants lay pheromone trails both when leaving the nest and when returning to the nest. Ants that are lucky enough to take a shorter foraging route return to the nest sooner, increasing the pheromone concentration of the route each way. In this way, shorter routes develop more concentrated pheromone trails faster, which attract more ants, which further increase pheromone concentration of the shortest routes. In this way, an ant colony can make an intelligent decision (take the shortest foraging route) without any individual doing anything more intelligent than following a simple rule (follow the strongest pheromone signal). Home is where the heart is. Photo of a bee swarm by Tom SeeleyHoneybee colonies also solve complicated tasks with the use of communication. Tom Seeley at Cornell University and his colleagues have investigated the honeybee group decision-making process of finding a new home. When a colony outgrows their hive, hundreds of scouts will go in search of a suitable new home, preferably one that is high off the ground with a south-facing entrance and room to grow. If a scout finds such a place, she returns to the colony and performs a waggle dance, a dance in which her body position and movements encode the directions to her site and her dancing vigor relates to how awesome she thinks the site is. Some scouts that see her dance may be persuaded to follow her directions and check out the site for themselves, and if impressed, may return to the hive and perform waggle dances too. Or they may follow another scout’s directions to a different site or even strike out on their own. Eventually, the majority of the scouts are all dancing the same vigorous dance. But interestingly, few scouts ever visit more than one site. Better sites simply receive more vigorous “dance-votes” and then attract more scouts to do the same. Like ants in search of a foraging path, the intensity of the collective signal drives the group towards the best decision. Once a quorum is reached, the honeybees fly off together to their new home.But groups can develop better solutions than individuals even without communication. Gaia Dell’Ariccia at the University of Zurich in Switzerland and her colleagues explored homing pigeon navigation by placing GPS trackers on the backs of pigeons and releasing them from a familiar location either alone or in a group of six. Because they were all trained to fly home from this site, they all found their way home regardless of whether they were alone or in a group. But as a flock, the pigeons left sooner, rested less, flew faster, and took a more direct route than did the same birds when making the trip alone. By averaging the directional tendencies of everyone in the group, they were able to mutually correct the errors of each individual and follow the straightest path. In each of these examples, each individual has limited and uncertain information, but each individual has information that may be slightly different than their neighbors’. By combining this diverse information and making a collective decision, hordes of idiots can make genius decisions.Want to know more? Check these out:1. Couzin, I. (2009). Collective cognition in animal groups Trends in Cognitive Sciences, 13 (1), 36-43 DOI: 10.1016/j.tics.2008.10.002 2....

Couzin, I. (2009) Collective cognition in animal groups. Trends in Cognitive Sciences, 13(1), 36-43. DOI: 10.1016/j.tics.2008.10.002

Goss, S., Aron, S., Deneubourg, J., & Pasteels, J. (1989) Self-organized shortcuts in the Argentine ant. Naturwissenschaften, 76(12), 579-581. DOI: 10.1007/BF00462870

Dussutour, A., Nicolis, S., Deneubourg, J., & Fourcassié, V. (2006) Collective decisions in ants when foraging under crowded conditions. Behavioral Ecology and Sociobiology, 61(1), 17-30. DOI: 10.1007/s00265-006-0233-x

List C, Elsholtz C, & Seeley TD. (2009) Independence and interdependence in collective decision making: an agent-based model of nest-site choice by honeybee swarms. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 364(1518), 755-62. PMID: 19073474

Dell'Ariccia, G., Dell'Omo, G., Wolfer, D., & Lipp, H. (2008) Flock flying improves pigeons' homing: GPS track analysis of individual flyers versus small groups. Animal Behaviour, 76(4), 1165-1172. DOI: 10.1016/j.anbehav.2008.05.022

It Doesn’t Always Pay to Kill Your Siblings

2012-04-18T10:55:20Z

A mother reed warbler feeding her "adoptive" murderous cuckoo chick. Does she really think this is her child? Photo by Per Harald Olsen on Wikimedia Commons.A woman, driven to not raise her own child, leaves her baby in another woman’s nursery, killing another baby that is there and replacing it with her own. As soon as the transplanted baby is strong enough, it slowly, methodically kills all the other children in the nursery, hording all of the adoptive mother’s attention for itself. With time, it grows needier and more demanding, running the poor adoptive mother ragged trying to care for the monstrous child that had murdered all her own children. It may sound like the plotline of a horror flick, but it happens every year among several egg-laying species (granted, maybe without quite so much anthropomorphism and drama). Animals that lay their eggs among the egg clutches of other species and benefit from the “hosts” parenting their young are called obligate brood parasites. Like the creepy narrative above, the still-naked, recently-hatched offspring of many obligate brood parasites attack and kill the offspring of their hosts to ensure more parental attention. Cuckoo chicks are well known to kill their “step-siblings” (the nestmates that are the chicks of their host parents) by pushing them out of the nest. Caution: Watching this BBC video can have emotional consequences: You may (depending on personal experiences) think that ensuring you are an only child would only increase your well-being. Interestingly, about a third of all avian obligate brood parasites don’t show this nestmate-killing behavior. This suggests that killing your nestmates may be advantageous in some circumstances, but disadvantageous in others. The shiny cowbird is another obligate brood parasite. It lays its eggs in the nests of over 200 different host species that vary in body size and lifestyle. An international research team, including Ros Gloag and Alex Kacelnik from the University of Oxford in the U.K. and Diego Tuero, Vanina Fiorini, and Juan Reboreda from the University of Buenos Aires, Argentina, set out to test whether the decision to kill or tolerate nestmates impacts cowbird chicks differently depending on the host species. The researchers observed the nests of two common shiny cowbird host species: the house wren, a much smaller host than the cowbird, and the chalk-browed mockingbird, a larger host than the cowbird. For each nest, they either placed a combination of one cowbird egg and a few host eggs, or one cowbird egg and a few artificial eggs. When the eggs hatched, this resulted in some cowbirds having host “step-siblings” and other cowbirds being “only children”. When the chicks were 4 days old and 8 days old, the researchers videotaped each nest, and measured how much food each chick was getting fed and each chick’s weight and tarsus length (that’s the length of one of the leg bones and gives a good method to compare body sizes in birds). This is a picture of begging chicks in a parasitized nest of a chalk-browed mockingbird, taken from a video. The chick with the smaller, redder gape at the top of the image is the cowbird. The other larger gapes belong to the mockingbird's own chicks. Photo by Ros Gloag.Overall, cowbirds grew to similar sizes at similar rates regardless of whether they were raised by mockingbird or house wren parents. But the presence or absence of nestmates had an interesting effect.Among cowbirds raised in mockingbird nests, cowbirds raised with nestmates faired far worse than cowbirds raised alone. Although mockingbird parents worked much harder and brought back more food to nests with more chicks (probably because the begging coming from the nest as a whole was much more rambunctious), cowbirds with mockingbird step-siblings had to share the provisions, whereas lone cowbird chicks got to eat everything the parents returned with. To make things worse, the mockingbird chicks grew faster than the cowbird chicks and they quickly outcompeted them. By the eighth day, cowbirds raised alone were larger and had higher survival rates than cowbirds raised with mockingbird step-siblings. This graph shows how much food the parents gave to the shiny cowbird chick, depending on whether the chick had mockingbird or wren parents and on whether it had nestmates (mixed) or was alone. The dashed bars show the total amount of food brought back to the nest for nests with nestmates. Notice that although nests with nestmates had the most food brought to the nest (dashed bars) in all cases, the shiny cowbird chicks with mockingbird parents got more food on day 8 if they were alone than if they had nestmates (solid bars) and the shiny cowbird chicks with wren parents got more food on day 8 if they had nestmates than if they were alone (solid bars). Graph from Gloag, et. al 2011 Behavioral Ecology paper.However, among cowbirds raised in house wren nests, cowbirds raised with wren step-siblings faired far better than cowbirds raised alone. As did the mockingbird parents, wren parents worked much harder and brought back more food to nests with more chicks. The cowbird chicks grew faster than the wren chicks, and so the cowbirds managed to eat more than their fair share of provisions. Additionally, sharing a nest with nestmates can have other benefits as well, such as helping to keep warm. As a result, cowbirds raised with wren step-siblings grew larger than cowbirds raised without wren step-siblings.We don’t yet know whether obligate brood parasite chicks with multiple host species adjust their strategy (kill or tolerate) depending on the size of the host chicks, but this study suggests that they might. If you are interested in science, this may be a topic you could explore.At any rate, killing your siblings or step-siblings probably isn’t a wise thing to do. They can help encourage our parents to do more for us, they can keep us warm, and when they’re not looking we can “borrow” their stuff. Besides, birds don’t have the same morals, ethics and court systems that we do.Want to know more? Check this out:...

Gloag, R., Tuero, D., Fiorini, V., Reboreda, J., & Kacelnik, A. (2011) The economics of nestmate killing in avian brood parasites: a provisions trade-off. Behavioral Ecology, 23(1), 132-140. DOI: 10.1093/beheco/arr166

Space Census Finds Extra Penguins, Poop

2012-04-13T14:20:02Z

Playing what might have been the world's most tedious game of Where's Waldo?, scientists used photos taken from space to count all the emperor penguins in Antarctica. They found more than a hundred thousand birds that hadn't been spotted before. The news may affect the penguins' fate in a warming world. Besides, what's a better surprise than extra penguins? Researchers from several institutions, including the British Antarctic Survey in Cambridge, undertook the emperor penguin space census. They thought previous penguin counts might not be accurate. For one thing, the last estimate of the Antarctic penguin population is almost 20 years old. For another, humans can't easily travel very far from their Antarctic research bases to seek out half-frozen bird huddles. So penguin colonies that are farther out in no man's land might have never been spotted by people. Thanks to emperor penguins' habit of clumping together in giant colonies during breeding season--and their convenient lack of camouflage against the snow--the researchers knew high-resolution satellite photos should reveal the penguins. They used images from all around Antarctica's coastline, where penguin colonies camp out. Forty-six colonies appeared, including several that hadn't been counted before. A penguin colony on the Antarctic coastline, spotted from above. After zooming in on each colony and sharpening the images, the researchers used computers to count the penguins one by one. The challenge was for the computer to decide which dark pixels represent penguins, rather than shadows on the snow--or penguin poop. Author Peter Fretwell explains that in this method, "you 'train' the computer to recognize the pixels that are penguin, guano, snow or shadow by giving it sample pixels. The computer then goes away and splits the whole image into each pixel type." Zooming in on a penguin colony and sharpening the image. I think I found the guano. As long as the images have a high enough quality, Fretwell says, this technique is "usually quite accurate." Where the satellite pictures were more shadowy, penguin counts would be a little less certain. For some of the colonies, though, researchers were able to check their numbers against estimates others had made from the ground or from aerial photography. And then there were the missing penguins. All the satellite images were taken during the breeding season, when emperor penguins congregate to create adorable new baby penguins. The new parents take turns babysitting: While one penguin takes care of the chick, the other goes out to sea and swallows lots of fish to regurgitate later. While the chicks are small, they spend most of their time balancing on top of their parents' feet to keep warm. Once the chicks are old enough to walk around on their own, both parents may leave to forage. So for every individual counted in a satellite photo, the authors assumed there was a hidden chick and a second adult at sea hunting for food. (They were only interested in counting breeding adults, not the chicks, most of which will die.) Later in the season, some of the penguin pixels may have been kids instead of adults. But since a young penguin standing on the ice probably has two parents away foraging, the researchers figured that pixel still stood for two adult penguins. The final count was about 595,000 adult emperor penguins in all of Antarctica. That's roughly the (human) population of Milwaukee. It's also substantially higher than the last estimate, which put the population between 270,000 and 350,000 adult birds. The census could easily have overestimated or underestimated the true number of penguins. But, Peter Fretwell says, "The main thing is that this gives us an initial benchmark from which we can monitor emperor penguin numbers in the long term." As climate change tightens its grip on every part of the globe--all the way to the poles--penguins will certainly see some changes around them. The sea ice along the coastlines they inhabit will disappear; shifting food webs may make their prey scarcer; and severe storms might become more frequent. Knowing how many emperor penguins are there now, and where to find their colonies, will help scientists monitor how the species is coping with the changes. We might even be able to keep them from becoming harder to find than Waldo. Fretwell, P., LaRue, M., Morin, P., Kooyman, G., Wienecke, B., Ratcliffe, N., Fox, A., Fleming, A., Porter, C., & Trathan, P. (2012). An Emperor Penguin Population Estimate: The First Global, Synoptic Survey of a Species from Space PLoS ONE, 7 (4) DOI: 10.1371/journal.pone.0033751 Image: Close-up penguins from Hannes Grobe/AWI/Wikimedia Commons; satellite images from Fretwell et al. Note for British readers: You may know Waldo as Wally....

Fretwell, P., LaRue, M., Morin, P., Kooyman, G., Wienecke, B., Ratcliffe, N., Fox, A., Fleming, A., Porter, C., & Trathan, P. (2012) An Emperor Penguin Population Estimate: The First Global, Synoptic Survey of a Species from Space. PLoS ONE, 7(4). DOI: 10.1371/journal.pone.0033751

Google Searches Give Away a Country's GDP

2012-04-10T11:02:02Z

Anytime we travel through the Internet we leave piles of data behind us, like Pigpen shedding his cloud of filth. It's too bad if you're concerned about privacy. But if you're a mathematician, that heap of dirt is more like a goldmine, and digging into it can turn up unexpected nuggets. A study of worldwide Google searches, for one thing, reveals that people in wealthier nations think less about the past. Google collects data on what search terms people around the world are using. Researchers who want to use this data to compare search terms across different countries are usually restricted to places that share a language. But the authors of a new paper in Scientific Reports got around that problem by looking only at numerical search terms. "We realized...that years represented in Arabic numerals are an almost universal written representation," author Helen Susannah Moat wrote in an email. By looking only at search terms such as 2011 or 2010, she and her coauthors could compare search data from nearly the whole globe. "It seemed a logical first step to consider to what extent Internet users were searching for dates in the future compared to dates in the past," Moat says. For example, looking at data from 2010, the researchers compared searches including 2011 to those including 2009. The ratio of forward-looking to backward-looking searches in each country became its "future orientation" score. The authors culled data from 45 countries with substantial Internet-using populations. Then they sorted those 45 countries by GDP ("also the most obvious variable," Moat says). A clear pattern popped out of the numbers: Countries with lower GDPs had lower future orientation scores, and vice versa. People in poorer countries did more searches concerning the previous year; those in wealthier nations searched more for the next year. The trend was strong, and it held up in data from 2009 and 2008 as well. Countries with the lowest future orientation scores included Pakistan and Vietnam, where previous-year searches outnumbered next-year searches by a factor of three or four to one. In the United States and Canada, countries toward the higher end in future orientation, searches for the last year and the next year were roughly equal. Switzerland, Australia, and the United Kingdom were among the most forward-looking countries of all. "One of the possible interpretations of our results," Moat writes, "is that a focus on the future supports economic success." In other words, populations that are more forward-thinking become wealthier. This up-by-the-bootstraps explanation doesn't seem like the simplest one, though. Another possibility is that populations with more money and leisure time can afford to spend it thinking about the future. A person in a wealthier nation might search online for next year's concert tickets, dates of work holidays, or when the new iPad is coming out. Someone without disposable income, though, might not have many such events to look forward to. Here's some good news for people in all nations: Google Trends is available online for aspiring data analysts to play with. Panning for gold in its graphs won't cost anything except your free time. Preis, T., Moat, H., Stanley, H., & Bishop, S. (2012). Quantifying the Advantage of Looking Forward Scientific Reports, 2 DOI: 10.1038/srep00350...

Preis, T., Moat, H., Stanley, H., & Bishop, S. (2012) Quantifying the Advantage of Looking Forward. Scientific Reports. DOI: 10.1038/srep00350