Mating behavior of Drosophila affinis : a test for geographic variation in intraspecific and interspecific mate discrimination

Two general models of the evolution of courtship behavior have been proposed; one emphasizes evolutionary stability while the other emphasizes evolutionary lability of mating signals and preferences. The documentation of geographic variation in mating behavior in a wide range of taxa provides support for the view that preferences and signals are subject to rapid evolution. A lack of geographic variation in mating behavior has also been documented for several species which suggests that the validity of the two opposing models of the evolution of courtship may depend on the system in question. Additional case studies are required to determine the generality of interpopulation divergence in mating behavior and to allow for comparisons of patterns between species.

In this study, I tested for the presence of geographic variation in Drosophila affinis, a woodland North American species. A total of 63 multiple mate choice tests were run between 21 D. affinis isofemale lines from eight geographic populations and a D. affinis tester stock from Tennessee. Drosophila affinis females have previously been reported to mate with a closely related species, Dathabasca, in the laboratory, suggesting the possibility of influence on mating behavior from interspecific interactions. To test for the presence of geographic variation in interspecific discrimination, I ran a series of multiple choice tests between nine D. affinis isofemale lines from seven geographic populations and a tester stock of D. athabasca from Tennessee.

There was no significant variation in D. affinis in either intraspecific and interspecific discrimination, which is noteworthy for two reasons. First, this study is one of the few that reports a lack of such variation in a Drosophila species. Second, extensive geographic variation in mating behavior has previously been documented in D. athabasca, an ecologically similar, close relative of D. affinis. I discuss possible reasons for the different patterns of variation found in the two species.