Gene flow in the European coal tit, Periparus ater (Aves: Passeriformes): low among Mediterranean populations but high in a continental contact zone

Abstract

Extant phylogeographical patterns of Palearctic terrestrial vertebrates are generally believed to have originated from glacial range fragmentation. Post-Pleistocene range expansions have led to the formation of secondary contact zones among genetically distinct taxa. For coal tits (Periparus ater), such a contact zone has been localized in Germany. In this study, we quantified gene flow between Fennoscandian and southern European coal tits using a set of 13 microsatellite loci. STRUCTURE analysis revealed four genetic clusters, two occurring on Mediterranean islands. German populations were genetically admixed but introgression of southern alleles was evident for Fennoscandian populations. In the south, we found negligible introgression of northern alleles (and haplotypes) but slight admixture of two southern genetic clusters in the Pyrenees and on the Balkan Peninsula and near complete sorting of these two allelic lineages on the islands of Corsica and Sardinia. Genetic distinctiveness of the Mediterranean island populations reflects general patterns of endemism in the Corso-Sardinian fauna and the Cypriot fauna. Wide-range gene flow in Central Europe suggests a broad zone of intergradation between subspecies of the coal tit rather than a narrow contact zone. This is in accordance with low morphological and bioacoustic differentiation of European coal tit populations.