March 20, 2009

No butterflies were harmed by this research

With a species using cryptic resemblance [camouflage] for its protection, the very existence of neighbours involves a danger to the individual, since the discovery of one by a predator will be a step in teaching it to recognize the crypsis. With an aposematic [bad-tasting, warning-coloration] species, on the other hand, the existence of neighbours is an asset, since they may well serve to teach an inexperienced predator the warning pattern. -- William Hamilton, 1964
This week's paper describes research that could have been a winning science fair project. "Does colour polymorphism enhance survival of prey populations?", published online by Lena Wennersten and Anders Forsman in Proceedings of the Royal Society, helps answer an interesting evolutionary question, using materials available in many kitchens.

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January 10, 2009

Grooming and groveling reduces meerkat stress

This week's paper is "Manipulating grooming by decreasing ectoparasite load causes unpredicted changes in antagonism" by Joah Madden and Tim Clutton-Brock, published on-line in Proceedings of the Royal Society.

Social animals often groom each other, removing parasites (lice, ticks, fleas, etc.) from places that may be hard for the beneficiary to reach, while also relaxing them, reducing heart rate and lowering concentrations of stress hormones. This stress-reducing function is sometimes considered more important than the hygenic one, but that made me ask, in an earlier post, why natural selection hasn't made lower (healthier) levels of stress the default. If stress is harmful and grooming isn't always available, why depend on grooming to reduce stress?

Madden and Clutton-Brock tested the interaction among parasites, grooming, and social interactions by chemically treating meerkats to eliminate parasites. Half of the meerkats got treated with an antiparasite chemical while the other half got water as a control, but parasite levels dropped in both. Maybe the chemical rubbed off on nontreated individuals.

With lower parasite loads, they only groomed each other half as much. Self-grooming also decreased. Because the social function of grooming was thought to be important, they expected increased fighting, bullying, etc., but that didn't happen overall. The biggest overall change in social interactions was a near-doubling in "unprompted submissions", basically groveling. Looking more carefully at pairwise interactions, they found some increases in dominance interactions, which were often followed by grooming of the dominant individual by the subordinate. So lower parasite levels led to less grooming, which led to stress, leading to cranky dominants, who were then placated by grooming they didn't really need (at least not for parasites) or general groveling. They concluded that

"for meerkats, grooming primarily serves a hygienic function, and secondarily provides a facultative response to antagonism, functioning to halt persistence or escalation of antagonism. This contrasts with its proposed function suggested for primates as a pre-emptive strategy that inhibits the initiation of antagonism by establishing or reinforcing a social structure."

November 28, 2008

We cooperators need to stick together

Experiments on the evolution of cooperation can be simpler with microbes than with animals. Microbes do sometimes cooperate. For example, some amoebae get together and form a stalk (consisting of hundreds of individual cells) to elevate spores (many more individual cells) above the soil. Bacteria may collectively produce and release enough extracellular enzymes to make food available for all, when none of them could make enough enzyme alone. But why should an amoeba volunteer to be in the stalk (an evolutionary dead end) rather than becoming a spore? And why not save the cost of making expensive extracellular enzymes, by free-loading on enzyme production by others? Out of the goodness of their hearts? They don't have hearts.

Cooperation is easiest to understand among microbes that share the same allele (one of several alternative versions of a gene) for cooperation. Kin-selection theory says that an allele leading to some individually costly activity may spread if it preferentially benefits others with the same allele, relative to those with different alleles. Cooperation among relatives, who are more likely to share a given allele, is therefore easy to understand.

But can microbes recognize kin, i.e., whether another microbe has the same alleles? Sometimes, apparently. In this week's paper, Elizabeth Ostrowski and colleagues report in PLoS Biology that Kin discrimination increases with genetic distance in a social amoeba.

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November 7, 2008

Can an NPR gene explain gregarious and solitary behavior?

This week's issue of Science has a special section on the genetics of behavior. In humans, at least, conflicting results seem to be common. According to the overview paper, one study found that people who were abused as children have a two-thirds chance of depression as adults, if and only if they also have a particular version of a serotonin transporter gene; an analysis of several studies on this gene rejected this conclusion, however. Other combinations of genes affecting testosterone and the rate at which certain brain chemicals break down may increase criminal activity, but maybe not. One company is already offering genetic testing of potential mates for a gene possibly linked to divorce. How soon will we see "in-vitro tourism", to countries that offer genetic modification of behavior-linked genes in human germ-line cells? Clinics that currently offer untested or dangerous "cancer cures" might not wait for answers to the many scientific, technical, and ethical questions that such services would raise. But genetic effects on behavior are complex and hard to predict, even in the simplest cases, as seen in this week's paper.

"npr-1 regulates foraging and dispersal strategies in Caenorhabditis elegans" was just published in Current Biology by Andrea Gloria-Soria and Ricardo Azevedo.
C. elegans is a tiny worm, barely visible without magnification. Two alleles of the npr gene produce two different versions of the NPR signal-receptor protein, differing in a single amino acid. (Despite the connection to signals, the NPR gene actually has as much to do with National Public Radio as the famous "sonic hedgehog" gene has to do with hedgehogs.)

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October 18, 2008

Cooperative fish, cheating ants

Cooperation is widespread in nature, despite theoretical predictions that "cheating" mutants could displace cooperators over just a few generations of evolution. We don't apply human moral standards to other species, of course, but define cheating as contributing less, while benefiting from activities of others. The evolutionary persistence of cooperation is usually attributed to reciprocity (trading resources or services) or to kin selection: cooperation among relatives, such as parental care, can persist even without reciprocity. Fish that clean parasites from other fish are a standard example of reciprocity -- they get to eat the parasites -- whereas nonreproductive worker ants are a standard example of kin selection. I will briefly discuss one recent paper on each of these.

Redouan Bshary and coauthors report in Nature that "Pairs of cooperating cleaner fish provide better service quality than singletons." Cleaner fish often prefer to eat client mucus (yum!) than client parasites, but clients don't like this and tend to leave. When a male and female cleaner work together, the client fish may leave if either of them takes a bite of mucus. Females, in particular, were less likely to do this when cleaning with their male partner rather than alone. The authors also did an experiment to see whether cleaner fish would eat a less-preferred food (fish flakes, perhaps analogous to client parasites) if eating their more-preferred food (prawns, perhaps analogous to client mucus) resulted in the food plate being taken away. They did, especially the females. This may have been because the male often chased her if she ate a prawn, costing them both the rest of their meal. Overall, pairs appear to provide better service to clients, because they are better-behaved together than alone, especially the female.

Shigeto Dobata and coauthors reported on "Cheater genotypes in the parthenogenetic ant Pristomyrmex punctatas" in Proceedings of the Royal Society. Social insects, such as ants and bees, usually have reproductive queens and nonreproductive workers. Worker genes are transmitted to the next generation by the queen, who is typically the workers' mother and therefore shares most of their genes. Pristomyrmex punctatas is different. An individual ant may reproduce (usually when young) and also work. Some individuals are more like queens, however. These are larger, reproduce more, and do little or no work for the colony. If these nonworking ants were close relatives of the workers, this behavior could perhaps be maintained by kin selection. It could be an example of division of labor for mutual benefit, a less-extreme version of the more-familiar worker/queen division. So Dobata and coauthors analyzed the DNA of hundreds of ants to see how they were related. They found that these nonworking ants were much less closely related to workers than queens usually are. Most of the ants (working or not) reproduced parthenogenetically, essentially cloning themselves without sex. Working hard while unrelated individuals profit from your work doesn't usually work out over the long run, but these nonworking ants have been seen in the field for over 25 years. Is this an evolutionary dead end? A similar situation with Cape honey bees, whose colonies are parasitized by unrelated "pseudoqueens" usually leads to colony extinction. I look forward to reading more about this interesting ant species.

October 10, 2008

Experimental evolution of predation and sexual attractiveness

Fossils and DNA-sequence comparisons among species are like fingerprints and other clues found at crime scenes. We can often draw reliable conclusions about past events (evolutionary or criminal) from such physical evidence, but some people prefer eyewitness accounts. So evolutionary biologists are increasingly doing experiments that let us see evolution in action. Evolution is a change over generations, so the short generation times of microbes make them especially useful for experimental evolution.

Two recent examples, both published in Proceedings of the Royal Society, are "Experimental evolution of a microbial predator's ability to find prey", by Kristina Hillesland, Greg Velicer, and Richard Lenski, and "Experimental evolution of a sexually selected display in yeast", by David Rogers and Duncan Grieg.

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September 12, 2008

Evolution of mental illness

I usually only discuss papers with original data, but I'm going to make an exception this week.

"Battle of the sexes may set the brain" was published in Nature by Christopher Badcock and Bernard Crespi. It's labeled "Opinion" but it is based on facts as well as theory. Their central hypothesis is that mental illness in humans is often the result of conflicts between genes inherited from the mother and father.

Imagine a gene -- let's call it IGF2, since that's it's name -- that causes a fetus to grow faster, resulting in somewhat higher birth weight. Babies with slightly higher birth weight tend to be healthier, up to a point, but they may endanger the health of the mother, at least a little. So most women shut down the copy of IGF2 in their eggs. Therefore, most babies get an active copy from their father and an inactive copy from their mother. Occasionally, though, the mother's copy is also active in the fetus, resulting in larger-than-normal babies. It turns out that these babies have a higher risk of autism.

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September 6, 2008

Conflict builds cooperation

I just heard an interesting talk by Joan Silk on lasting friendships among female baboons, in which grooming and mutual support during conflicts are both important. Here's a link to some of her papers. This week's paper is on a somewhat-related topic, but in birds rather than apes.

"Duration and outcome of intergroup conflict influences intragroup affiliative behaviour" was just published in Proceedings of the Royal Society by Andrew Radford, of the University of Bristol.

Woodhoopoes are African birds (videos here) that live in small groups, typically a breeding pair and some close relatives. Conflicts over territory with neighboring groups (mostly yelling at each other) are common, often more than once a day. Neighbors rarely take over each other's territories, but if they win the shouting match they stay and forage for awhile. Do such conflicts and their outcomes affect group solidarity?

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August 21, 2008

The bird in the mirror

This week’s paper is “Mirror-induced behavior in the magpie (Pica pica): evidence of self-recognition?, by Helmut Prior and colleagues, available online in PLoS Biology.

When confronted with mirrors, apes (including humans) react very differently from monkeys. Monkeys never seem to recognize that they are seeing a reflection of themselves rather than another monkey. Recently, dolphins and elephants have been added to the list of species that can recognize themselves in mirrors and use them for self-exploration. Most other species can not. Is this because their brains are too small? Or is the tendency to self-exploration using a mirror a side-effect of a mental ability that evolved for other reasons? If the latter is true (even if there is also some minimum brain size requirement), then more species that need to pay more attention to what others of their species are doing might be more likely to evolve this mental ability.

Some birds, for example, hide food, raid each other’s food caches, and pay attention to who was around when they were hiding food. How do these birds respond to mirrors?

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May 31, 2008

Traditional values in bees

The beehive was an early Mormon icon, symbolizing hard work and cooperation. To an evolutionary biologist, however, a beehive could symbolize reproductive skew, a situation where some individuals reproduce much more than others. Extreme reproductive skew is one of the defining characteristics of eusocial species, of which honey bees are a prime example. Reproductive skew can differ between the sexes. In honey bees, the queen lays most of the eggs, and most females don't reproduce at all. Polygamous species and groups show the opposite pattern: males vary much more in reproductive success than females do. Maybe an inverted beehive would have been a better symbol. Note that the cells in our bodies behave somewhat like a eusocial bee colony; any children we have are directly descended from a few sex cells, while brain cells and skin cells play the supporting role of worker bees.

This week's paper, "Ancestral monogamy shows kin selection is key to the evolution of eusociality" was published in Science by William Hughes and others. Like humans, some bees are monogamous, meaning that the queen mates with only one male, so her daughters (the workers) are all sisters. In other bee species, the queen mates with several males, so her daughters are half-sisters. Relatedness generally favors cooperation, although there are some possible complications, discussed below.

This week's paper asks how mating behavior affects the evolution of eusociality. They reasoned that, if mating system doesn't matter, then today's eusocial species could be descended from either monogamous, polygamous, polyandrous (each female has multiple mates), or promiscuous ancestors. Alternatively, eusociality may evolve more easily with one of these mating systems than with the others.

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May 16, 2008

Sex! Identity theft! Burying beetles!

The "Coolidge effect" - I would have named it for a different American president - is a tendency of some males to be more interested in a new sex partner than one they have mated with in the past. Males that don't help care for young may have more descendants this way than if they put all their eggs (so to speak) in one basket. But to avoid remating with the same partner, one first needs to remember them all.

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April 19, 2008

Separate vacations and other sexual differences

Three recent papers in Proceedings of the Royal Society discuss differences between males and females or, in one case, among males.

"The costs of risky male behaviour: sex differences in seasonal survival in a small sexually monomorphic primate" by Cornelia Kraus and others, is based on a 10-year study of differences between male and female behavior in grey mouse lemurs. During the breeding season, males had lower survival than females, despite any possible risks associated with pregnancy or raising young. The higher risk for males apparently resulted from their tendency to travel more, looking for females.

The sexes also differ in winter behavior: females hibernate, while males remain active. Is there something about female physiology that makes hibernation healthier for them than it would be for males? Maybe, but there was no difference in winter survival between the sexes, which don't differ much in size in this lemur species. The authors suggest that hibernation might have longer-term benefits in females, such as increased lifespan, whereas males need to stay active to bulk up in preparation for the breeding season.

This paper reminded me of an earlier paper on albatrosses, in which "in each pair, the male spent the winter just north of the pack ice in Antarctic waters whereas the female stayed south of Madagascar." It's not hard to understand why males and females might differ in various ways (size, color, etc.) but differences in behavior outside of the breeding season are more interesting.

The second paper addresses an old argument between Charles Darwin and Alfred Russel Wallace, who developed similar explanations of evolution by natural selection at about the same time.

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November 25, 2007

Conflict over parental care

My wife and I have been watching the Planet Earth series. Week after week, mother polar bears and mother snow leopards care for their young, while fathers are either absent or dangerous. But then we got to Emperor penguins. What's the difference? This week's paper Parental conflict in birds: comparative analyses of offspring development, ecology and mating opportunities tries to answer this question.

Every baby bird -- except some turkeys -- has two parents. How much care does each parent provide for their chicks, and why? If animal behavior were ordained by a god, as a guide to human behavior, then we might expect all wild species to exhibit the same exemplary behavior. Or maybe those species that have more opportunities to interact with and influence humans -- ducks, say -- would exhibit divinely inspired behavior, while those remote from human settlements -- Emperor penguins, for example -- are left to the whims of natural selection?

The authors of this week's paper didn't waste time testing such nature-as-morality-lesson hypotheses, which are left as an exercise for creationists. Instead, they explored how parental care behaviors have evolved in response to various factors. These factors include how chicks of different species depend on parental care, and also whether a bird that leaves its mate alone to care for their chicks has additional opportunities to reproduce.

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November 9, 2007

When hybrids are best

This week's paper is Facultative Mate Choice Drives Adaptive Hybridization by Karin Pfennig of the University of North Carolina, Chapel Hill (where I went to kindergarten), published in Science.
Spadefoot Toad (Wikipedia)

In contrast with the "hybrid vigor" sometimes seen with crosses between different genotypes within a species -- corn, for example -- hybrids resulting from mating between related species are usually less likely to survive and reproduce. For example, when two different species of spadefoot toad mate, their daughters usually produce fewer eggs. But apparently there are situations where genes from the other species are beneficial enough to outweigh problems due to genetic incompatibilities.

When Spea bombifrons females mate with Spea multiplicata males, their tadpoles mature faster. This is beneficial in shallow ponds that don't last long, but not in deeper ponds, which will last long enough for nonhybrid tadpoles to mature. Therefore, the smart thing for S. bombifrons females to do would be to mate with their own species in deeper ponds, but with S. multiplicata in shallower ponds. But how smart is the average toad?

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