Did Polyommatus icarus (Lepidoptera: Lycaenidae) have distinct glacial refugia in southern Europe? Evidence from population genetics

Pleistocene climatic oscillations strongly influenced the genetic composition of many species which are often divided into several genetic lineages. In this context, we studied the allozymes of a common and widely distributed butterfly, the common blue Polyommatus icarus, over a large part of Europe. The species had a rather high genetic diversity within populations with a strikingly high mean number of alleles per locus (2.98). In contrast, differentiation between populations was very low (FST: 0.0187). Only a marginal trend of decline in genetic diversity from the south to the north was observed. Isolation‐by‐distance existed on a European scale (r = 0.826), but not at a regional level. Regional differentiation between populations in western Germany was extremely low (FST: 0.0041). It is probable that P. icarus was widely distributed in the Mediterranean region during the last ice age and expanded into central Europe in the postglacial period without major genetic erosion. Moderate present and past gene flow in an intact metapopulation structure may have occurred on local, regional and perhaps even continental scales. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80, 529–538.