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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.?

October 14, 2011

Inclusive fitness, punishment, migration, dinosaurs

Here are some papers that looked interesting this week:
The validity and value of inclusive fitness theory

Costly punishment prevails in intergroup conflict

Migration by soaring or flapping: numerical atmospheric simulations


A late-surviving basal theropod dinosaur from the latest Triassic of North America

The Diets of Early Hominins

Hibernation is associated with increased survival and the evolution of slow life histories among mammals

Successful Transmission of a Retrovirus Depends on the Commensal Microbiota

October 10, 2011

This week's picks

I've been traveling and and have another trip coming up, but things should calm down after that. Meanwhile, evolutionary biology marches on.
Inferring the Tree of Life: chopping a phylogenomic problem down to size?

Deciphering the genetic basis of animal domestication

Detecting shifts in diversity limits from molecular phylogenies: what can we know?

A Map of Local Adaptation in Arabidopsis thaliana

The intriguing evolutionary dynamics of plant mitochondrial DNA

Extensive divergence of yeast stress responses through transitions between induced and constitutive activation

Host-parasite relationships in the genome

MHC genotypes associate with resistance to a frog-killing fungus

Sex-specific differential survival of extra-pair and within-pair offspring in song sparrows, Melospiza melodia

Infrared mapping resolves soft tissue preservation in 50 million year-old reptile skin