Abstract
The rate at which populations adapt depends on the probability and time of fixation of beneficial alleles. Both of these quantities can be significantly impacted by population subdivision and limited gene flow. However, how limited dispersal through its combined effects on the probability and time to fixation influences the rate of adaptation via hard and soft sweeps remains understudied. We investigate this here using the diffusion approximation and simulations. In contrast to previous suggestions, we find that adaptation may take on average fewer generations under limited dispersal than under panmixia. This is especially true if adaptation occurs via hard sweeps of recessive alleles, and dispersal is not too limited (such that approximately FST < 0.25). The reason is that such mildly limited dispersal leads to only a moderate increase in effective population size (which slows down fixation), but is sufficient to cause a relative excess of homozygosity due to inbreeding, thereby exposing rare recessive alleles to selection (which accelerates fixation). We also explore the effect of meta-population dynamics through local extinction followed by recolonization, finding that such dynamics always accelerate adaptation via soft sweeps, while hard sweeps exhibit faster fixation interspersed with longer waiting times. Finally, we discuss the implications of our results for the detection of sweeps, suggesting that limited dispersal mitigates the expected differences between the genetic signatures of sweeps involving recessive and dominant alleles.
