Limited hybridization along a large contact zone between two genetic lineages of the butterfly Erebia medusa (Satyrinae, Lepidoptera) in Central Europe

Genetic lineages evolving during glacial isolation frequently come into contact as the result of postglacial range expansions. Hybridization often occurs along these contact zones. In Europe, the high mountain systems of the Alps and Pyrenees are well known for their hybrid belts. This article studies the contact zone of the Woodland Ringlet Erebia medusa in a Hercynian mountain area in the Czech-German border region not exceeding 1500 m a.s.l. Hybrid populations between an eastern and a western genetic lineage were detected by AMOVA-based tests, principal component analysis and neighbour joining analysis. Over most of the range of the Czech-German Border Mts, the ridges separate the western and the eastern genetic lineage from each other. However, two important hybrid areas were detected: (1) the watershed of the Ohre river in the north-west of that area, a major valley system passing through these mountains and (2) the high plateaux of the Sumava Mts in the south-east, an extended area of high elevation. The location of hybrid populations in geographical vicinity to non-hybrid populations and the generally low F-IS (2.1%) make reduced fitness of hybrid individuals little likely. The hybrid populations have intermediate genetic diversity between the genetically poor western and the genetically rich eastern lineage populations.