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March 29, 2013

Persistent polymorphisms, enhancing mutation, new fossils, cooperation & conservation

All five of my Darwinian Agriculture lectures at the International Rice Research Institute are now available on YouTube.

Here are some interesting papers published this week.

Multiple Instances of Ancient Balancing Selection Shared Between Humans and Chimpanzees " In addition to the major histocompatibility complex, we identified 125 regions in which the same haplotypes are segregating in the two species [neither version has displaced the other in either species in 6 million years], all but two of which are noncoding [i.e., they probably control other genes rather than coding for a protein]." The most likely explanation for such prolonged co-existence is that individuals with less-common alleles may be resistant to pathogens that have evolved to attack those with more-common alleles.

Accelerated gene evolution through replication-transcription conflicts" "We propose that bacteria, and potentially other organisms, promote faster evolution of specific genes through orientation-dependent encounters between DNA replication and transcription."

Palaeontology: Tubular worms from the Burgess Shale"

Preservation of ovarian follicles reveals early evolution of avian reproductive behaviour"

Both information and social cohesion determine collective decisions in animal groups

Governance regime and location influence avoided deforestation success of protected areas in the Brazilian Amazon

Wild Pollinators Enhance Fruit Set of Crops Regardless of Honey Bee Abundance

March 1, 2013

Copying in birds, dolphins, and viruses; evolution & environmental change; evolution of mutation rate

Learning and signal copying facilitate communication among bird species "where only two species regularly interact, one species' [alarm] calls incorporate the call of the other."

Vocal copying of individually distinctive signature whistles in bottlenose dolphins "Copying occurred almost exclusively between close associates such as mother-calf pairs and male alliances during separation... copies were clearly recognizable as such because copiers consistently modified some acoustic parameters of a signal when copying it... no evidence for the use of copying in aggression or deception."

A bacteriophage encodes its own CRISPR/Cas adaptive response to evade host innate immunity "the only documented bacterial adaptive immune system is the CRISPR/Cas... a phage-encoded CRISPR/Cas system is used to counteract a phage inhibitory chromosomal island of the bacterial host. "

Evolutionary rescue from extinction is contingent on a lower rate of environmental change" "By assessing fitness of these engineered [E. coli] strains across a range of drug concentrations, we show that certain genotypes are evolutionarily inaccessible under rapid environmental change."

Fossil evidence for a hyperdiverse sclerophyll flora under a non-Mediterranean-type climate "sclerophyll hyperdiversity has developed in distinctly non-Mediterranean climates... likely a response to long-term climate stability."

A trade-off between oxidative stress resistance and DNA repair plays a role in the evolution of elevated mutation rates in bacteria "The dominant paradigm for the evolution of mutator alleles in bacterial populations is that they spread by indirect selection for linked beneficial mutations when bacteria are poorly adapted... [but] hydrogen peroxide, generates direct selection for an elevated mutation rate in the pathogenic bacterium Pseudomonas aeruginosa as a consequence of a trade-off between the fidelity of DNA repair and hydrogen peroxide resistance."


August 10, 2012

Fossils, convergent evolution, cooperation, and "groundwater footprints"

New fossils from Koobi Fora in northern Kenya confirm taxonomic diversity in early Homo "The new fossils confirm the presence of two contemporary species of early Homo, in addition to Homo erectus, in the early Pleistocene of eastern Africa."

A transitional snake from the Late Cretaceous period of North America "...snakes evolved from burrowing lizards. The skull is intermediate..."

Community-wide convergent evolution in insect adaptation to toxic cardenolides by substitutions in the Na,K-ATPase The same molecular change to a sodium pump, previously seen in Monarch butterflies, was found in four insect species (separated by 300 million years of evolution) feeding on plants making the same natural insecticides.

Heterogeneous networks do not promote cooperation when humans play a Prisoner's Dilemma "1,229 volunteers chosen among last year's high school students"

Water balance of global aquifers revealed by groundwater footprint" "80 per cent of aquifers have a groundwater footprint that is less than their area" but "the global groundwater footprint is currently about 3.5 times the actual area of aquifers", putting water supplies for 3.5 million people at risk. My book briefly compares the ecological footprints of conventional and organic farms.

August 3, 2012

Defense against malaria, cuckoos, mobile elements, and creationists

Fighting malaria with engineered symbiotic bacteria from vector mosquitoes
"symbiotic bacteria to deliver antimalaria effector molecules to the midgut lumen"

PLoS Biology: The Evolutionary Consequences of Blood-Stage Vaccination on the Rodent Malaria Plasmodium chabaudi
"recombinant blood stage malaria vaccines can drive the evolution of more virulent malaria parasites"

Cuckoos Combat Socially Transmitted Defenses of Reed Warbler Hosts with a Plumage Polymorphism
"social learning is specific to the cuckoo morph that neighbors mob"

Function, Targets, and Evolution of Caenorhabditis elegans piRNAs
evolving defenses against active mobile elements

A complete insect from the Late Devonian period
400 million years ago? Like 400 million years (to three significant digits) before the Earth was created?

March 30, 2012

The tortoise and the tortoise

This week's paper is "Embryonic communication in the nest: metabolic responses of reptilian embryos to developmental rates of siblings", published in Proceedings of the Royal Society by Jessica McGlashan and others.

Turtle eggs deeper in a nest are exposed to lower temperatures. Since they don't regulate their own temperature and since the rate of development depends on temperature, you might expect these eggs to hatch later than those above them. If their older siblings leave first, that could reveal the location of the nest to hungry predators. Some turtle species have solved this problem -- all the turtles emerge together, in contrast to what would be predicted by differences in temperatures to which they were exposed.

The authors of this paper tested the hypothesis that some form of communication between eggs is involved. They exposed eggs to different temperatures, to get different stages of development, then mixed them to see whether the less-advanced eggs accelerated their development when mixed with more-developed eggs.

Mixing with more-developed eggs led to higher respiration rates and heart rates, both of which were measured noninvasively. You might expect that accelerating hatching would lead to problems, but apparently not: the baby turtles were just as good at righting themselves after being turned over.

It would be interesting to compare the question of synchronous emergence in turtles versus germinating seeds. A group of seeds might mostly come from the same mother plant. So, like turtles, they would have fairly high genetic relatedness, which would tend to promote cooperation. But a seed that germinates a little sooner than its neighbors may end up shading them all season. What about turtles? The last turtle to reach the water may have the highest risk of predation, but the first one isn't necessarily safer than those in the middle. Adult trees may benefit from synchronizing their seed production, for predator-saturation reasons similar to those that apply to turtles. But for seed germination, the benefits of being first may outweigh any benefits of synchrony.
turtle.JPG

January 12, 2012

Flycatchers use early birds (great tits) to crowd-source clutch size

A bird that tries to raise too many chicks this year may not survive to reproduce again. So there's a tradeoff between current and future reproduction. Earlier, I discussed how stress hormones over-worked mothers pass to their chicks decrease survival of this year's chicks, whereas the reduced work-load can increase the mother's life-long reproduction. But how many chicks is too many? It depends on food supply and other conditions that vary from year to year.

Rather than researching conditions themselves, flycatchers could wait to see how many eggs other flycatchers lay. This is the approach many humans use to decide how much to invest in stocks, but it doesn't work any better for the flycatchers than it does for us. By the time they figure out what others are doing, it's too late to take advantage of the information.

An alternative crowd-sourcing approach is to see how many eggs were laid by another species of bird that finishes egg-laying a bit earlier. Indeed, Jukka Forsman and colleagues report, in a recent paper in Biology Letters, that "Observed heterospecific clutch size can affect offspring investment decisions."

Continue reading "Flycatchers use early birds (great tits) to crowd-source clutch size " »

October 28, 2011

Copy-protection strategies in birds

Brood parasites lay their eggs in the nests of other birds, typically of a different species. Why don't those birds recognize the foreign eggs and kick them out of the nest? The parasitic species have often evolved so that their eggs look much like those of their hosts. Can the host species evolve to recognize the intruders? This week's paper discusses two different evolutionary responses.

"How to evade a coevolving brood parasite: egg discrimination versus egg variability as host defences" was published by Claire Spottiswoode and Martin Stevens under Proceedings of the Royal Society's open-access option, so you can read the details for yourself here.

They compared three species of bird parasitized by different species of African finch. Individuals of one host species varied enormously in the appearance of their eggs, as shown below. The parasitic finches apparently don't match their eggs to the particular host individual, so their eggs would often be a poor match. But this host isn't as good at recognizing slightly different eggs, relative to a host that produces less-variable eggs. This difference between species is consistent with the hypothesis that the species with less-variable eggs was under stronger selection for ability to recognize subtle differences.
eggs.jpg
A statistician might point out that, however many birds they sampled of each species, any conclusions about correlations between species-level traits (egg variability among individuals and detection of visual differences) would need to be based on a larger number of species. But until someone comes up with a counter-example, I'll assume their conclusions are probably right, although not proven.

Speaking of correlations, the most-downloaded paper from that journal also deals with parasitism and intelligence. The authors of "Parasite prevalence and the worldwide distribution of cognitive ability" found that average IQ is lowest in countries with highest frequency of infectious disease. They argue that the metabolic cost of fighting disease leaves less energy for developing brains. Even if disease does affect brain development, I wonder whether energy is the key factor. They also suggest that increases in average IQ over decades may be due to reduced disease. Again, it seems like these two variables could interact in a variety of ways, especially if we are talking about national averages. Disease affects economies which affect prenatal care, nutrition, education, etc.?

March 25, 2011

The beaks of the finches

This week's paper is "Divergence with gene flow as facilitated by ecological differences: within-island variation in Darwin's finches", published in Philosophical Transactions of the Royal Society.

"If humans evolved from chimps", ask the creationists, "why are there still chimps?" Good question! Humans didn't evolve from modern chimps, any more than I am descended from my cousins. We just share ancestors.

But still... why are there now chimps and humans, rather than one species? More generally, how does one species split in two? If part of a species becomes isolated enough to be inaccessible for mating, or at least "geographically undesirable," then the two populations can diverge through natural selection or random genetic drift, eventually losing the ability to reproduce with each other.

But genetic divergence doesn't always require geographical isolation. For example, if birds with medium-size beaks get less food than those with large or small beaks (on an island with many large and small seeds but few medium seeds), will the resulting "disruptive selection" tend to split the population into two subpopulations, with genes for small and large beaks? Maybe, but not if small- and large-beaked birds interbreed, combining genes for large and small beaks. And why wouldn't they?

Continue reading "The beaks of the finches" »

February 10, 2011

Evolution of cooperation, disease, relatives, birds...

Some recent papers that look interesting:

The evolution of host protection by vertically transmitted parasites

Cooperation among non-relatives evolves by state-dependent generalized reciprocity

Before senescence: the evolutionary demography of ontogenesis

Costs of memory: lessons from 'mini' brains

Land inheritance establishes sibling competition for marriage and reproduction in rural Ethiopia

Major global radiation of corvoid birds originated in the proto-Papuan archipelago

Within and transgenerational immune priming in an insect to a DNA virus

Multiple strategies in structured populations

Long-term isolation of a highly mobile seabird on the Galapagos

May 28, 2010

Sexual imprinting in redheads

We may disagree on who's most attractive, but most of us prefer to mate with a member of our own species. But that can be tricky for redheads. Redhead mothers often lay their eggs -- I'm talking about ducks, of course -- in canvasback nests, saving themselves the trouble of raising the chicks. But what if chicks raised by canvasbacks end up thinking of themselves as canvasbacks? Or, however, they may think of themselves, what if their earlier experience makes them prefer canvasbacks as mates? They might end up mating with the wrong species.

This apparently doesn't happen very often in nature, but why not? One possibility is that redheads are genetically programmed to prefer redheads, even if they grow up with canvasbacks. After all, brush turkeys grow up to prefer mating with brush turkeys (below), even though they're incubated in compost piles managed mostly by males. Michael Sorenson, Mark Hauber, and Scott Derrickson, the authors of this week's paper, "Sexual imprinting misguides species recognition in a facultative interspecific brood parasite", published in Proceedings of the Royal Society, set out to test this hypothesis for redheads.
BushTurkey.JPG
BushTurkeyMound.JPG
Brush turkey and brush turkey mound in Australia. Photo by Ford Denison.

Continue reading "Sexual imprinting in redheads" »

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.

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

September 20, 2008

Who suffers from stress?

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?" »

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?

Continue reading "Conflict builds cooperation" »

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?

Continue reading "The bird in the mirror" »

June 18, 2008

Guest blog: The Peacock's Tale

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" »

March 15, 2008

100th post: reversing evolution II: mimicry in snakes

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" »

March 9, 2008

Tricky parasites winning the evolutionary arms race

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" »

January 29, 2008

Choosy mothers may choose wisely

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" »

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.

Continue reading "Conflict over parental care" »

July 28, 2007

Begging: the question

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" »

June 10, 2007

Rock-paper-scissors for high stakes

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" »

June 3, 2007

Scientific controversy: dinosaur-tail soup ?

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?

The two elements of evolutionary theory that upset creationists most wouldn't be affected at all, of course. Our confidence that the universe is a million times older than Bible-based estimates, and that humans and chimps share a recent common ancestor, is based on multiple lines of evidence for each, none of it dependent on which dinosaurs had feathers, if any.

But what about the claim that birds are descended from dinosaurs? Let's see what a leading textbook, "Evolutionary Analysis", says. Page 44: Sinosauropteryx had what "some paleontologists believe are primitive feathers." Page 45: they cite several papers, one questioning this conclusion. "More convincing are [true feathers on] the dromesaur fossils." Page 553: "Luis Chiappe (1995) used skeletal characters to infer the phylogeny [family tree] of early bird lineages." The tree shown has protofeathers near the base, followed by true feathers. If the P. Roy. Soc. paper is correct, that would only require revising the earliest branches of his tree.

So this is a real controversy, but it's only a controversy about where feathers appeared in the family tree of dinosaurs and birds. As the paper says, "the wider question of whether or not birds originate from dinosaurs does not concern the present study." The main fossil evidence that they did comes from analysis of skeletons, not feathers. We don't have DNA from dinosaurs, but genetic comparisons among living species suggest that birds are more closely related to crocodiles than to mammals (Science 283:998). So birds-from-dinosaurs still seems likely.

The second paper is "Context dependence in the coevolution of plant and rhizobial mutualists" by Katy Heath (heat0059@umn.edu) and Peter TIffin, whose lab is next to mine. Among other things, this paper shows that plants infected by two different strains of rhizobium bacteria often grew less than those infected only with the worst of the two strains. This result may become controversial soon, when Toby Kiers and I publish data apparently showing that plants infected by two different strains can grow more than those infected with only the best strain. Our experiments were done with soybean, whereas theirs used a wild relative of alfalfa, which houses rhizobia in a different type of root nodule (see photos). Also, our two strains were much more different than theirs. So maybe this doesn't really qualify as a controversy, at least not yet.

AlfalfaNodules5.jpg

TrefoilNodules2.jpg

Nodule photos taken in our lab (c) Inga Spence... licensing from www.alamy.com.

When there is a controversy, should it be taught? We certainly shouldn't teach a conclusion as certain when it is still (genuinely) controversial. And students should learn about some past scientific controversies, to understand how they were resolved. The triumph of evolution would be a good example. Exposure to some current controversies would be good, too, assuming teachers have time to keep up with the literature, well enough to know what has been settled (at least until convincing new data to the contrary are published) and what is still controversial. I remember Professor Spanswick, at Cornell. telling us "I found the evidence for the chemiosmotic hypothesis convincing, but always presented it as a controversy... until Mitchell won the Nobel Prize for it."

May 29, 2007

Coevolution and gene flow

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" »

May 14, 2007

Evolution of babysitting in bluebirds

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" »

April 25, 2007

Bigger males, or smaller females?

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?" »