Gene flow and selection in a natural population of Drosophila melanogaster.

A marked genetic differentiation to the presence of alcohol in the environment has been shown to occur between inside cellar and adjacent outside sections of a vineyard population of D. melanogaster (McKenzie and Parsons 1974). Estimates of migration during the vintage period suggest considerable movement occurs from outside into the cellar and that the most tolerant genotypes are the most successful migrants. A quantitative model of this system suggests that the selection intensity may not be a limiting factor in maintaining the differentiation. It also suggests that gene flow must be restricted between sections of the population at all but vintage periods if this differentiation is to persist.