Genetic evidence for adaptation-driven incipient speciation of Drosophila melanogaster along a microclimatic contrast in "Evolution Canyon," Israel

Substantial genetic differentiation, as great as among species, exists betw een populations of Drosophila melanogaster inhabiting opposite slopes of a small canyon. Previous work has shown that prezygotic sexual isolation and numerous differences in stress-related phenotypes have evolved between D. m elanogaster populations in "Evolution Canyon," Israel, in which slopes 100- 400 m apart differ dramatically in aridity, solar radiation, and associated vegetation. Because the canyon's width is well within flies' dispersal cap abilities, we examined genetic changes associated with local adaptation and incipient speciation in the absence of geographical isolation. Here we rep ort remarkable genetic differentiation of microsatellites and divergence in the regulatory region of hsp70Ba which encodes the major inducible heat sh ock protein of Drosophila, in the two populations. Additionally, an analysi s of microsatellites suggests a limited exchange of migrants and lack of re cent population bottlenecks. We hypothesize that adaptation to the contrast ing microclimates overwhelms gene flow and is responsible for the genetic a nd phenotypic divergence between the populations.