Gene flow and adaptive potential in Drosophila melanogaster

Gene flow among historically isolated populations is expected to increase genetic diversity and consequently the ability of populations to adapt to environmental changes. Few experimental studies, however, have examined the relationship between gene flow and the adaptive potential of populations. The increase in adaptive potential that occurs as a result of gene flow is expected to depend on the genetic variance among populations that undergo genetic exchange. In the present study, we compared observed and expected changes in adaptive potential (as measured by the selection response of sternopleural bristle number) that occur as a result of gene flow among experimental populations of Drosophila melanogaster. We examined the effect of limited immigration (m = 0.05 over 3 generations) among a set of experimentally isolated lineages, in addition to the effect of complete hybridization among lineages. As expected, we found that limited immigration and hybridization both yielded increases in adaptive potential. However, whereas the effect of limited immigration agreed well with theoretical expectations, the increase in adaptive potential following complete hybridization of lineages was significantly less than expected. We discuss these findings in relation to endangered species conservation efforts, particularly with respect to the goal of maximizing the retention of adaptive potential within managed populations.