adaptive evolution

Gossmann TI, Keightley PD & Eyre-Walker A 2012 The effect of variation in the effective population size on the rate of adaptive molecular evolution in eukaryotes. Genome Biol Evol 4:658-667.

• adaptation is to some extent limited by the supply of mutations
• at least some adaptation depends on newly occurring mutations rather than on standing genetic variation

• the rate of adaptive evolution is expected to be proportional to N_es if N_es≫1
• there is evidence of widespread adaptive amino acid substitutions in species such as Drosophila, house mice, bacteria, and some plant species with large N_e
• there is little evidence in hominids and other plant species that appear to have small N_e
• there are, however, some exceptions
• maize, for example, has a relatively large effective population size, approaching that of wild house mice, but shows little evidence of adaptive protein evolution
• the yeast Saccharomyces paradoxus, which presumably has a very large N_e, also shows little evidence of adaptive protein evolution
• Drosophila simulans does not appear to have undergone more adaptive evolution than D. melanogaster, even though it is thought to have a larger N_e

• the positive correlation between ω_a and N_e is consistent with a model in which the rate of adaptive evolution is limited by the supply of new mutations
• the correlation seems less consistent with a model in which adaptation comes from standing genetic variation (Pritchard et al. 2010; Pritchard and Rienzo 2010)