Ecology and genetics of interspecific hybridization in the swallowtails, Papilio hospiton Géné and P. machaon L., in Corsica (Lepidoptera: Papilionidae)

Abstract The Corsican swallowtail butterfly, Papilio hospiton , is endemic to Corsica and Sardinia (France and Italy) and included in the list of endangered species by the Washington Convention. It is spread all over Corsica in scattered populations linked to diverse habitats. A study by enzyme electrophoresis showed that the genetic diversity of the species is of the same order of magnitude as that of Papilio machaon from continental France and Corsica. The differentiation between populations is rather low, which is consistent with the high vagility of the adults. Natural hybridization between P. hospiton and P. machaon is frequent, and laboratory crosses show that the hybrids are not sterile. However, developmental perturbations impair the viability of further hybrid progenies. Although limited introgression between the two species is likely to take place, enzyme electrophoresis and PCR-RFLP analysis of mitochondrial DNA show that their gene pools remain distinct. Genetic assimilation by P. machaon therefore does not seem to be a threat for P. hospiton .