A Natural Population Derived from Species Hybridizationin the Drosophila ananassae Species Complexon Penang Island, Malaysia

We surveyed natural population of the Drosophila ananassae species complex on Penang Island, Malaysia. Analyses of phenotypic traits, chromosome arrangements, molecular markers, and reproductive isolation suggest the existence of two species: D. ananassae and D. cf. parapallidosa. Molecular marker analysis indicates that D. cf. parapallidosa carries chromosome Y and 4 introgressions from D. ananassae. Thus, D. cf. parapallidosa seems to be a hybrid descendant that recently originated from a natural D. parapallidosa♀× D. ananassae♂ cross. Furthermore, D. cf. parapallidosa behaves differently from authentic D. parapallidosa with respect to its reproductive isolation from D. ananassae. Premating isolation is usually seen in only the D. ananassae♀× D. parapallidosa♂ cross, but we observed it in crosses of both directions between D. ananassae and D. cf. parapallidosa. In addition, hybrid males from the D. ananassae♀× D. parapallidosa♂ cross are usually sterile, but they were fertile when D. ananassae♀ were mated with D. cf. parapallidosa ♂. We attempted an artificial reconstruction of the hybrid species to simulate the evolutionary process(es) that produced D. cf. parapallidosa. This is a rare case of natural hybrid population in Drosophila and may be a useful system for elucidating speciation with gene flow.