Genital coupling and copulatory wounding in the Drosophila rufa species complex: comparison with the D. auraria species complex (Diptera: Drosophilidae)

In sexually reproducing animals, genital morphology is usually divergent among closely related species, which can lead to a mismatch of genital coupling (i.e. mechanical isolation). The montium species group of the subgenus Sophophora is the largest clade in Drosophila and is a useful model in which to study the evolution of genital morphology. This group includes a pair of sister clades, i.e. the Drosophila auraria and Drosophila rufa species complexes. The former includes four species with overlapping distributions, and the latter consists of five species that are almost allopatric. The previous study on the D. auraria complex suggested genital co-evolution between sexes (female structures accepting for or protecting from male structures). To test the generality, we analysed the D. rufa complex and three outgroup species. In the D. rufa complex, we detected genital structures corresponding between sexes, and copulatory wounds with species-specific positions. Given that approximately the same number of evolutionary changes in the genital traits were detected in both sexes of the two clades, we conclude that selection pressure to avoid interspecific mating (reproductive character displacement) is not a prerequisite for rapid genital co-evolution.