INTERSPECIFIC HYBRIDS OF DROSOPHILA HETERONEURA AND D. SILVESTRIS I. COURTSHIP SUCCESS

Drosophila heteroneura and D. silvestris are well‐defined, sympatric species of the planitibia subgroup of Hawaiian Drosophila. D. silvestris can be subdivided into two allopatric morphotypes that differ in the number of bristle rows on the front tibia (two rows versus three rows). We measured courtship success of intraspecific and interspecific hybrids as the proportion of females inseminated during a two‐week period with a single sib male. Proportions were arcsin‐transformed so that the values were asymptotically normal in distribution, and tests of homogeneity and of mean differences were performed. Of key importance is the discovery of genetic variation for the proportion of inseminated females within both D. heteroneura and D. silvestris . The interspecific crosses and the D. silvestris intraspecific crosses also provide evidence for a coadapted gene complex with some dominance or heterosis. This coadapted gene complex correlates with the morphotypes of these flies, rather than with the D. heteroneura/D. silvestris contrasts per se. This observation stresses the importance of recognizing both behavioral and morphological components of the mate‐recognition system. The incompatible coadaptation that separates the two‐row from the three‐row forms also supports recent molecular studies which indicate that the three‐row form split from the two‐row form prior to the split between D. heteroneura and two‐row D. silvestris . The observations of intraspecific variability and coadaptation support the predictions of a genetic‐transilience model which explains the origin of a new mate‐recognition system in terms of sexual selection in the context of a founder‐flush event.