This Week in Evolution

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

Continue reading "No butterflies were harmed by this research" »

Posted by R. Ford Denison at 10:36 PM | Permalink | Comments (0)

Recently, I wrote about how grooming each other can reduce levels of stress hormones, for example, in baboons and birds. But I asked, “why should natural selection allow excessive levels of this stress hormone?�
This week’s paper shows one way that natural selection can lead to harmful levels of stress hormones. The question, of course, is “harmful to whom?�

Writing in American Naturalist, Oliver Love and Tony Williams report that stressed mother birds pass stress hormones to their offspring. (Passing your stress on to others seems to be popular in humans also.) These hormones increase the risk of chicks dying, especially male chicks. But they may also increase the mother’s lifetime reproductive success.

Continue reading "Who suffers from stress?" »

Posted by R. Ford Denison at 11:10 PM | Permalink | Comments (3)

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?

Continue reading "Conflict builds cooperation" »

Posted by R. Ford Denison at 7:31 PM | Permalink | Comments (0)

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?

Continue reading "The bird in the mirror" »

Posted by R. Ford Denison at 5:38 PM | Permalink | Comments (1)

This week's post is by Dave Wisker, a graduate student in Molecular Ecology at the University of Central Missouri.

It's the creationist's dream. If actual evidence of creation is too much to hope for, how about a peer-reviewed paper in a respected journal overturning one of the icons supporting a major element of Darwin's theory?. Sexual selection in peafowl is definitely one of those icons. There appeared to be ample empirical evidence that peahen's preference for more elaborate trains on their mates has led to the spectacular male tail displays we see today. A series of papers in the 1990's by behavioral ecologist Marion Petrie and others seemed to solidly support this, and there is also evidence that elaborate tails may indicate good genes (Petrie et al, 1991; Petrie and Williams, 1993;.Loyau et al, 2005a). This, in itself, is a challenge to an older idea that the peacock's tail shows how arbitrary female preferences can be amplified to extremes by a "runaway"? process (Fisher, 1958). But, whatever their evolutionary origin, the preference itself has rarely been questioned.

However, a recent paper published in Animal Behaviour (http://tinyurl.com/4t69v5), "Peahens do not prefer males with more elaborate trains"?, challenges the conventional wisdom.

Continue reading "Guest blog: The Peacock's Tale" »

Posted by R. Ford Denison at 2:26 PM | Permalink | Comments (4)

This is a kilometerstone of sorts: my 100th post! Also, cumulative visits passed 10,000 this week. I know some blogs get more hits than that in only one day, but I used to spend hours preparing a lecture for 25 students, so I guess it's worthwhile to write a blog post for 10,000/100=100 readers. My readership trend over months seems to be slightly downward, however; I hope that's due to other blogs are getting better and readers having limited time, rather than my posts getting worse. Maybe I should be spending the time on my research or my Darwinian Agriculture book instead.

I recently wrote about mimicry in butterflies, then saw an interesting paper on how natural selection and migration affect mimicry in snakes. Selection and migration ("gene flow") are two of the four main processes responsible for evolutionary changes in the frequency of alternative genes in populations; the other two are the random ("drift") processes that can have a big effect in small populations but get smoothed out in large populations and, of course, mutation.

Selection and gene flow often act in opposite directions, because animals migrating into an area (or seeds or pollen blowing in) tend to be less well adapted to their new home, relative to animals or plants that have been evolving there. This general rule held up in this week's paper, as evident from the title: "Selection overrides gene flow to break down maladaptive mimicry", written by George Harper and David Pfenning and published in Nature.

Continue reading "100th post: reversing evolution II: mimicry in snakes" »

Posted by R. Ford Denison at 6:37 PM | Permalink | Comments (14)

Two papers this week describe recently discovered sophisticated adapatations of two different parasites: Gall insects can avoid and alter indirect plant defenses, published in New Phytologist by John Tooker and colleagues, and Parasite-induced fruit mimicry in a tropical canopy ant, published in American Naturalist by Steve Yanoviak and colleagues (if you're in a hurry, skip to the end for amazing photos).

Various plants recruit "bodyguards" when attacked by insects. For example, when caterpillars start munching on corn (maize) plants, the plants (including uninjured leaves) release gaseous chemicals called terpenoids. These terpenoids attract parasitic wasps, which lay their eggs into the caterpillars. This eventually kills the caterpillars, which presumably benefits the plant. But what if the caterpillars could prevent the plant from signaling to the wasps? As far as I know, caterpillars haven’t evolved this trick (yet), but there are apparently some insects – the Hessian fly, Mayetiola destructor (say) – that do not trigger signaling when they feed on wheat plants. There are at least two possible explanations…

Continue reading "Tricky parasites winning the evolutionary arms race" »

Posted by R. Ford Denison at 11:24 PM | Permalink | Comments (1)

Two papers on sexual selection in birds this week:
Adaptive Plasticity in Female Mate Choice Dampens Sexual Selection on Male Ornaments in the Lark Bunting , published in Science by Alexis Chaine and Bruce Lyon, and Natural and sexual selection against hybrid flycatchers, published in Proceedings of the Royal Society by Nina Svedin and colleagues.

Continue reading "Choosy mothers may choose wisely" »

Posted by R. Ford Denison at 12:10 AM | Permalink | Comments (2)

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.

Continue reading "Conflict over parental care" »

Posted by R. Ford Denison at 7:44 PM | Permalink | Comments (0)

My wife and I have a bird feeder outside our kitchen window. Yesterday I saw an adult male cardinal feeding some of the seed to an immature cardinal not much smaller than he was. I guess it's hard to say "no", but should he have?

This week's paper, "The adaptive value of parental responsiveness to nestling begging" by Uri Gordzinski and Arnon Lotem, published online in Proceedings of the Royal Society, may have answered this question.

Continue reading "Begging: the question" »

Posted by R. Ford Denison at 12:38 AM | Permalink | Comments (4)

Chapter 3 of The Origin of Species is titled "Struggle for Existence", which Darwin uses "in a large and metaphorical sense including dependence of one being on another, and including (which is more important) not only the life of the individual, but success in leaving progeny." Differences among plants and animals in their success in leaving progeny depends on their adaptation to the physical environment, but also their interactions with each other. For example, "A plant which annually produces a thousand seeds, of which only one of an average comes to maturity [this must be true, if population size is constant], may be more truly said to struggle with the plants of the same and other kinds which already clothe the ground."

If the traits that maximized survival and reproduction were always the same, those with those best traits would quickly displace those with alternative traits. But changes in the physical and biological environment mean that no one genotype is consistently best. This week's paper is about frequency-dependent selection, where the fitness of each genotype depends on how common it is. If less-common genotypes tend to increase in frequency, no single genotype will take over.

Continue reading "Rock-paper-scissors for high stakes" »

Posted by R. Ford Denison at 2:05 AM | Permalink | Comments (0)

This week I want to talk about scientific controversies. In politics or religion, any difference of opinion may qualify as a controversy, which some may try to "settle" by killing those with opposing views. Most scientists would agree that unsupported opinion isn't enough to make a scientific controversy. A scientific question is controversial only if people are actually publishing data that seem to lead to different conclusions.

Two papers in press in Proceedings of the Royal Society illustrate current scientific controversies. The first is "A new Chinese specimen indicates that 'protofeathers' in the Early Cretaceous theropod dinosaur Sinosauropteryx are degraded collagen fibers" by Theagarten Lingham-Soliar (linghamst@ukzn.ac.za) and colleagues at the Universities of KwaZulu-Natal and North Carolina and the Chinese Academy of Sciences.

The title pretty much says it all. (Collagen is what gives shark-fin soup its distinctive texture, hence the title of this entry.) If the conclusions in this paper become generally accepted, how would that change our overall understanding of evolution?

Continue reading "Dinosaur-tail soup?" »

Posted by R. Ford Denison at 5:17 PM | Permalink | Comments (8)

Two species coevolve when changes in either lead to changes in the other. This includes “arms races� between species that compete with each other, but also interactions that benefit both species. “Gene flow� is the movement of genes from one population into another, of the same or related species. For example, some genes in modern cows seem to have come from mating with wild aurochs, before they went extinct. Gene flow often provides new genes; some may be useful to the recipient population. For example, pollen from transgenic sugar beets could transfer herbicide resistance (along with other crop genes) to related weed beets. More often, genes that were useful in the source environment may be harmful to the recipient population. Natural selection will tend to eliminate these, unless gene flow rates are too high. For example, if plants growing on toxic soil around an old mine are outnumbered by neighbors on nontoxic soil nearby, gene flow may swamp natural selection, preventing evolution of tolerance to toxic soil.

This week I’ll discuss a review article on coevolution and then an experimental paper showing how gene flow can affect coevolution. The review is “Variable evolution� by Elizabeth Pennisi, published in the May 4 issue of Science. It discusses coevolution of wild parsnip with the webworms that eat them and coevolution of pine trees with birds and squirrels, among other topics.

Continue reading "Coevolution and gene flow" »

Posted by R. Ford Denison at 3:31 AM | Permalink | Comments (4)

Major transitions in evolution have often involved loss of independence, as discussed last week. Most female bees work to increase their mother’s reproduction, rather than laying eggs themselves. Less extreme examples of helping others reproduce are known in some animals. “Kin selection� favors helping relatives, if the cost of helping is less than the benefit to the one helped, times their relatedness to the helper. This is known as Hamilton’s Rule. As Haldane put it, “I would jump into a river to save two brothers or eight cousins.� “Cost� and “benefit� are measured in number of offspring and “relatedness� is relative to one’s usual competitors. If surrounded by cousins, Hamilton’s Rule would lead to helping only siblings.

For helping behavior to have evolved, there must have been genetic variation in helpfulness. This week’s paper shows that this is still true for western bluebirds in Oregon.

Continue reading "Evolution of babysitting in bluebirds" »

Posted by R. Ford Denison at 6:10 PM | Permalink | Comments (4)

As you may have noticed, males and females look different in many species. In “brood parasite� cuckoos, those members of the cuckoo family that lay their eggs in nests of other "host" species, males are mostly bigger and more colorful than females. Did males become bigger and more colorful over the course of evolution? This could be due to sexual selection, based on female choice or conflict between males. Or, did females become smaller and less colorful? That could be due to coevolution with the host species. Less colorful females are less likely to be noticed hanging around host nests, and smaller females may lay smaller eggs that are harder for hosts to tell from their own eggs.

This week’s paper is “The evolution of sexual dimorphism in parasitic cuckoos: sexual selection or coevolution?� by O. Kruger and colleagues at the University of Cambridge and Boston University, published online in Proceedings of the Royal Society.

Continue reading "Bigger males, or smaller females?" »

Posted by R. Ford Denison at 6:11 PM | Permalink | Comments (3)