Feces and phylogeny

A couple of weeks ago I wondered aloud about the question of whether diet-related changes in the nature of gut bacteria could have significant effects in evolution.  The paper I was writing about at the time showed that flies fed different diets quickly began to prefer mates who had been fed the same diet, and this preference appeared to be due to a change in the composition of gut bacteria.  But is the composition of gut bacteria maintained over evolutionary timescales? A recent paper (Ochman et al. 2010.  Evolutionary relationships of wild hominids recapitulated by gut microbial communities.  PLoS Biology doi:10.1371/journal.pbio.1000546) suggests that it is; but the role of diet remains unclear.

Is it me you like, or my bacteria?

When two populations of a species evolve in different directions — perhaps because they live on separate islands, with different food sources or different dangers — at some point individuals from the two populations become unwilling to mate with each other.  This can increase the rate at which the two populations diverge, and thus the chance that they will actually become separate species.   A recent paper (Sharon et al. 2010 Commensal bacteria play a role in mating preference of Drosophila melanogaster, PNAS doi: 10.1073/pnas.1009906107) suggests that developing a mating preference may be much easier than we thought, and can be due not to genetic change but to changes in the bacteria carried by the population.