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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.
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.?


Really, these disease affect brain development?

I'll check this paper later.


How many species were sampled?

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