Genetic structure of French populations of the mountain butterfly Parnassius mnemosyne L. (Lepidoptera: Papilionidae)

Geographical variation in allozyme frequencies among 24 populations of the butterfly Parnassius mnemosyne in southern France was studied by enzyme electrophoresis. Clustering procedures were used to define the geographical organization of genetic variation and an analysis of genetic differentiation was performed to test the degree of potential gene flow between the colonies using the methodologies derived from F-statistics and the private alleles model. Further, an approach using reduced space ordinations (factorial analysis of correspondences and discriminant analysis), was used to allow the visualization of genetically intermediate populations and to determine the rôles of individual alleles at various levels of geographical structure. In P. mnemosyne , the effect of both isolation by distance and geographical barriers upon gene flow is complex. Some barriers appear to be very efficient, but others, at least as strong geographically, do not act in such a way. Multivariate analyses underlined the progressive transition between some groups while in other instances, a sharp cut was observed without obvious topographical barriers. Ecogeographical data and historical events (such as colonization processes) should probably be taken into account in order to explain the geographical variation of genetic structure.