GENETIC-BASIS OF MALE-STERILITY IN HYBRIDS BETWEEN 2 CLOSELY RELATED SPECIES OF DROSOPHILA

D. simulans and D. mauritiana are closely related sibling species, the former cosmopolitan and the latter restricted to the small oceanic island of Mauritius. Genetic analysis of male sterility in hybrids between these species shows that at least 5 loci (one on each chromosome arm) are responsible for this reproductive isolation. This is the most loci that were detected with the techniques used and implies that the true genetic divergence for sterility is even greater. The effects of chromosome segments on the character are roughly additive, with the X-linked segment making the largest contribution to sterility. The large effect of X chromosomes on male-limited reproductive isolation and the frequent limitation of hybrid sterility to males may be attributable to fertility interactions between X and Y chromosomes. These results parallel what was found in other Drosophila species and relate to recent theories of how reproductive isolation evolves in small founder populations.