The Balkans and the colonization of Europe: the post-glacial range expansion of the wild boar, Sus scrofa

Aim We focus on the biogeographical role of the Balkan Peninsula as a glacial refugium and source of northward post-glacial dispersal for many European taxa. Specifically, we analysed the genetic structure and variation of wild boar (Sus scrofa) samples primarily from Greece, a region that has repeatedly served as a glacial refugium within the Balkan Peninsula. Location Continental Greece, the Aegean island of Samos and Bulgaria. Methods We analysed wild boar samples from 18 localities. Samples from common domestic breeds were also examined to take into account interactions between wild and domesticated animals. Phylogenetic analyses were carried out on a 637-bp fragment of the mitochondrial DNA control region in 200 wild boar and 27 domestic pigs. The sequences were also compared with 791 Eurasian wild boar and domestic pig D-loop sequences obtained from GenBank. Results Ninety-four haplotypes were identified in the European wild boar data set, of which 68 were found in the Balkan samples and assigned to two previously described clades: the E1 European and Near Eastern clades. All of the continental samples clustered in the E1 clade and the samples from Samos fell into the Near Eastern clade, consistent with the island's proximity to Asia Minor. Intriguingly, 62 novel haplotypes were identified and are found exclusively in the Balkans. Only six haplotypes were shared between wild boar and domestic pigs. Main conclusions Our data reveal numerous novel and geographically restricted haplotypes in wild boar populations, suggesting the presence of separate refugia in the Balkans. Our analyses support the hypothesis of a postglacial wild boar expansion consistent with the leading edge model, north and west from modern day Greece, and suggest little maternal introgression of Near Eastern and domestic haplotypes into wild Balkan populations.