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November 9, 2012

Cooking key to cognition; corals recruit bodyguards; etc.

Metabolic constraint imposes tradeoff between body size and number of brain neurons in human evolution "This limitation was probably overcome in Homo erectus with the shift to a cooked diet."

Corals Chemically Cue Mutualistic Fishes to Remove Competing Seaweeds "Mutualistic gobies and corals appear to represent a marine parallel to terrestrial ant-plants, in that the host provides shelter and food in return for protection from natural enemies."

Bateman in Nature: Predation on Offspring Reduces the Potential for Sexual Selection "substantial yearly variation in the Bateman slope [number of offspring as a function of the number of mates] due to predation on fawns was evident."

Drift-barrier hypothesis and mutation-rate evolution "selection appears to reduce the mutation rate... to a level that scales negatively with both the effective population size (Ne)... and the genomic content "


For a list of my upcoming talks around the world, see my new Darwinian Agriculture Blog.

April 8, 2011

This week's picks

Workers influence royal reproduction
"worker aggressive and non-aggressive behaviour towards queens predicted which queen monopolized reproduction. In contrast, among-queen interactions were rare and did not predict queen reproduction. Furthermore, parentage analysis showed workers favoured their mother when present"
[Maybe "inclusive fitness" is useful after all!]

Updated chronology for the Miocene hominoid radiation in Western Eurasia
"Eurasian pongines [orangutans and extinct relatives] and African hominines [humans, chimps, bonobos, and extinct relatives] might have independently evolved in their respective continents from similar kenyapithecin ancestors [apes living 14 million years ago], resulting from an early Middle Miocene [5-23 MYA] intercontinental range extension followed by vicariance [geographic separation, reducing or eliminating interbreeding so allowing evolutionary divergence]. "

Ribozyme-Catalyzed Transcription of an Active Ribozyme "we recombined traits evolved separately in different ribozyme [catalytic enzyme made of RNA rather than protein] lineages. This yielded a more general polymerase ribozyme that was able to synthesize a wider spectrum of RNA sequences, as we demonstrate by the accurate synthesis of an enzymatically active RNA, a hammerhead endonuclease ribozyme. "

An evolutionary process that assembles phenotypes through space rather than through time "assortative mating between fast-dispersing individuals at the invasion front results in an evolutionary increase in dispersal rates in successive generations"

Fork-tailed drongos use deceptive mimicked alarm calls to steal food
"false alarm calls when watching target species handling food, in response to which targets flee to cover abandoning their food"

Moving calls: a vocal mechanism underlying quorum decisions in cohesive groups
"a sharp increase in the probability of changing foraging patch when the number of group members joining the chorus increased from two up to three"

Differences in the temporal dynamics of phenotypic selection among fitness components in the wild "The consistency in direction and stronger long-term average strength of selection through mating success and fecundity suggests that selection through these fitness components should cause more persistent directional evolution relative to selection through survival."

Rapid Spread of a Bacterial Symbiont in an Invasive Whitefly Is Driven by Fitness Benefits and Female Bias "Rickettsia sp. nr. bellii swept into a population of an invasive agricultural pest, the sweet potato whitefly, Bemisia tabaci, in just 6 years. Compared with uninfected whiteflies, Rickettsia-infected whiteflies produced more offspring, had higher survival to adulthood, developed faster, and produced a higher proportion of daughters. The symbiont thus functions as both mutualist and reproductive manipulator. "

The evolutionary biology of child health "cancer, the primary cause of non-infectious childhood mortality, mirrors child growth rates from birth to adolescence, with paediatric cancer development impacted by imprinted genes"

Tradeoffs associated with constitutive and induced plant resistance against herbivory "Across all 58 plant species, we demonstrate a tradeoff between constitutive and induced resistance, which was robust to accounting for phylogenetic history of the species. Moreover, the tradeoff was driven by wild species and was not evident for cultivated species."

Towards a quantitative understanding of the late Neoproterozoic carbon cycle
"all of the main features of the carbonate and organic carbon isotope record can be explained by the release of methane hydrates from an anoxic dissolved organic carbon-rich ocean into an atmosphere containing oxygen levels considerably less than today"

March 4, 2011

Sex, sexiness, viruses, nematodes, and horses

Haploinsufficiency and the sex chromosomes from yeasts to humans
"orthologues of S. cerevisiae HI genes (those for which a reduction in copy number in a diploid from two to one results in significantly reduced fitness) are significantly under-represented on the X chromosomes of mammals... accumulation of HI genes on the sex chromosomes would compromise fitness in both sexes, given X chromosome inactivation in females"

Natural selection stops the evolution of male attractiveness
"lack of genetic variation that would allow an increase in sexual fitness while simultaneously maintaining nonsexual fitness"

A Virophage at the Origin of Large DNA Transposons

Computational and phylogenetic validation of nematode horizontal gene transfer

Dietary Change and Evolution of Horses in North America

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" »

October 23, 2009

Experimental evolution of sex (revised)

"I show that a similar cost of sex exists when asexual mutants arise... but not when the species is a self-fertile hermaphrodite.... Although individual fitness (expected reproductive success) is assumed to be equal for sexual and asexual females, the heritability of fitness is... twice as high in asexual females" -- Richard Michod, Darwinian Dynamics

I should be working on my book, but a paper that just came out in Nature got me thinking about sex. A population with half males and half females will grow only half as fast as one consisting only of females that self-fertilize or clone themselves. So, many people have asked why sex evolved.

That's an interesting question, but I'm not sure about the rationale. As noted by Michod, a population of self-fertilizing hermaphrodites doesn't have any intrinsic growth advantage over a population of hermaphrodites that mostly cross-fertilizes. So is the problem sex, or males?

Evolutionary changes in gene frequency over generations depend on whether individuals with a given gene survive and reproduce more than other members of their population, not on the consequences for overall population growth. (Individuals can move between populations.) So we really have two related questions:
1) why do genes for producing male offspring persist? and
2) why do genes for cross-fertilization persist in species that can self-fertilize?

From an individual perspective, it's not apparent that producing male offspring is always a bad idea. Do couples with two sons have fewer descendants than those with two daughters? It can depend on the sex ratio in the population. If a human couple produces one offspring of whichever sex is in the minority, their offspring may have an easier time finding a mate.

But what about cross-fertilization? If a female cloned herself, her offspring would have all of her genes, rather than just half of them. So the frequency of genes for self-fertilization would tend to increase, unless individuals resulting from cross-fertilization were more likely to survive and reproduce. An offspring with half as many of one's genes, but a 2.1-fold better chance of survival (maybe because a sexual partner contributes different disease-resistance genes) gives a greater increase in fitness. So, one key to understanding the evolution of sex (cross-fertilization) is to measure the survival of individuals with one parent versus two, under conditions that plausibly occurred at critical points in a species ancestry.

This week's paper, "Mutation load and rapid adaptation favour outcrossing over self-fertilization", set out to "recapitulate the evolutionary process under the specific conditions predicted to favour either selfing or outcrossing." Levi Morran, Michelle Parmenter, and Patrick Phillips used the nematode, C. elegans, which consists of males and hermaphrodites. (This mix, and the lack of pure females, suggests there can be individual benefits to maleness, whatever the consequences for the population as a whole.) They used genetic manipulation to make populations that only self-fertilized or never self-fertilized, exposed them to high mutation rates or to a bacterial pathogen, and let them evolve.

Continue reading "Experimental evolution of sex (revised)" »

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.

Continue reading "Experimental evolution of predation and sexual attractiveness" »

August 15, 2008

What's that smell?

I'm back from vacation, which included a closeup look at this research submarine with Q&A by an expert technician, and seeing the family of our next president in a beach park. But lots of interesting work accumulated while I was gone, so my comments on this week's paper will be brief. You can read the whole thing on line.

"MHC-correlated odour preferences in humans and the use of oral contraceptives" was published in Proceedings of the Royal Society by Craig Roberts and colleagues. This is another women-sniffing-tee-shirts paper, but with some interesting new results.

Continue reading "What's that smell?" »

June 29, 2008

Evolution 2008: sexy plants, battling bacteria, durable cooperation

About 1500 scientists attended Evolution 2008 here last week. The four-day meeting was filled with 15-minute talks (usually ten at once, in different rooms), plus two evening poster sessions (like a science fair, for grownups, with discussions rather than judging), scenically located on a pedestrian bridge over the Mississippi. Reports that “scientists are abandoning evolution�? appear to be exaggerated.

Here are summaries of some of the talks I enjoyed.

Continue reading "Evolution 2008: sexy plants, battling bacteria, durable cooperation" »

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" »

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.

Continue reading "Separate vacations and other sexual differences" »

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" »

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?" »