population genetics
Leffler EM, Bullaughey K, Matute DR, Meyer WK, Ségurel L, Venkat A, Andolfatto P & Przeworski M 2012 Revisiting an old riddle: what determines genetic diversity within species? PLoS Biol 10:e31001388.
- species with larger population sizes may have more standing variation with which to respond to novel selection pressures, leading to a smaller fraction of adaptations from new mutations
- species with larger geographic ranges may be more likely to adapt through multiple, geographically restricted mutations than by global sweeps
- adaptation may have less of an effect in reducing variation than expected under assumptions of panmixia and selection on new mutations
- a possible explanation for the narrow range of diversity levels is that nuclear mutation rates per generation vary inversely with effective population size
- (e.g., due to more effective selection for a lower mutation rate in species with higher effective population sizes)
- the nuclear mutation rate per generation ranges over 100-fold
- 3.3 × 10−10 per site in Saccharomyces cerevisiae
- 3.5 × 10−9 in Drosophila melanogaster
- 1.3 × 10−8 in Homo sapiens
- 3.8 × 10−8 in Mus musculus
- (with the caveat that the per generation mutation rate may not be the relevant time-scale for S. cerevisiae)
- this explanation seems unlikely to entirely resolve the riddle
