Sexual isolation between Drosophila melanogaster, D-Simulans and D-mauritiana: sex and species specific discrimination

The sexual isolation among the related species Drosophila melanogaster, D. simulans and D. mauritiana is asymmetrical. While D. mauritiana males mate well with both D. melanogaster and D. simulans females, females of D. mauri tiana discriminate strongly against males of these two species. Similarly, D. simulans males mate with D. melanogaster females but the reciprocal cros s is difficult. Interspecific crosses between several populations of the th ree species were performed to determine if (i) males and females of the sam e species share a common sexual isolation genetic system, and (ii) males (o r females) use the same genetic system to discriminate against females (or males) of the other two species. Results indicate that although differences in male and female isolation depend on the populations tested, the isolati on behaviour between a pair of species is highly correlated despite the var iations. However, the rank order of the isolation level along the populatio ns was not correlated in both sexes, which suggests that different genes ac t in male and female sexual isolation. Neither for males nor for females, t he isolation behaviour of one species was paralleled in the other two speci es, which indicates that the genetic systems involved in this trait are spe cies-pair specific. The implications of these results are discussed.