Assortative mating in Drosophila adapted to a microsite ecological gradient.

Elucidating the causes of population divergence, and ultimately speciation, is a central objective of evolutionary biology. A number of previous studies of Drosophila populations from the Nahal Oren canyon (Mt Carmel, Israel) revealed significant interslope differences for a complex of fitness and behavioral traits. Peculiarities in courtship song patterns and nonrandom mating were observed, despite a small interslope distance. Single and multiple mate choice tests with D. melanogaster from the opposite slopes displayed highly significant assortative mating, with preference for sexual partners from the same slope. Here we report the results on mate choice in the sibling species D. melanogaster and D. simulans inhabiting Nahal Oren canyon. Significant assortative mating was found in both species. Genetic heterogeneity in mate choice was found among the isofemale lines of D. melanogaster. Samples of isofemale lines established from females collected in spring and fall seasons show the same mating patterns.