| Abstract: | Climatic oscillations influence the distribution of species in time. Thermophilic species survived the ice ages in
refugia around the Mediterranean. Northern Africa is one of the possibly important refugia. In this study we test the
genetic differentiation between northern African and European populations, using the marbled white butterfly species
complex, Melanargia galathea/M. lachesis, as a model. We studied 18 allozyme loci in 876 individuals from 23
populations representing a major part of Europe (northern Spain to Romania) and the western part of northern Africa
(Atlas Mountains). The African populations resemble the European ones in allelic richness; their genetic diversity is
higher than in Europe. Cluster analysis discriminated five European genetic groups: M. lachesis, a western European
lineage, and three eastern European lineages. However, the African samples did not form a separate cluster within this
phenogram, but clustered randomly within the Balkan/southeastern European groups. The genetic differentiation
among the African populations (FST 8.8%) was higher than that within any of the European lineages (FST 2.6–5.5%).
The high genetic diversity and the relatively strong differentiation of the four African populations sampled in a
comparatively limited area of the Atlas Mountains indicate that the most probable origin of M. galathea is northern
Africa, with its sibling species, M. lachesis, evolving in parallel in Iberia. Most probably, M. galathea colonised Europe
first during the Eem interglacial, some 130 ky ago. Since M. lachesis must have existed on the Iberian peninsula during
that period already, M. galathea should have reached Europe via Italy. The genetic differentiation to distinct groups in
Europe most probably evolved during the following Wu¨ rm glacial period.
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