Multiple Pleistocene refugia and postglacial colonization in the European chub (Squalius cephalus) revealed by combined use of nuclear and mitochondrial markers
|Type:||Article in Periodical|
|Keywords:||cytochrome b; Europe; freshwater fishes; glacial refugia; microsatellites; phylogeography; population structure|
The patterns of nuclear and mitochondrial genetic variation in the European chub, Squalius cephalus (Linnaeus, 1758) was analyzed, in order to understand the evolutionary history of this species and to test biogeographical hypotheses for the existence of co-distributed European freshwater fish species. We genotyped 12 polymorphic microsatellite markers derived from 310 individuals collected from across the distribution of S. cephalus in Europe and sequenced mtDNA from a subset of 75 individuals. Sequences of mtDNA cytochrome b were analysed using both phylogenetic and population genetic methods. Geographical structure in microsatellite loci was examined using a distance method (FST), factorial correspondence analysis (FCA) and a Bayesian clustering method. The mtDNA network showed a clear split into four different haplogroup lineages: Western (separated into Atlantic and Danubian sublineages), Eastern, Aegean (occurring in two distinct sublineages in the Balkans and in Spain) and Adriatic. Our results indicate recent population expansion in the Eastern and Western Atlantic lineages and the admixture of two previously separate sublineages (Atlantic and Danubian) in the Western lineage. Bayesian structure analysis as well as FCA results roughly corresponded to the mtDNA-based structure, separating the sampled individuals into almost non-overlapping groups. Our results support hypotheses suggesting origins of extant lineages of freshwater fishes in multiple-refugia and the subsequent postglacial colonization of Europe via different routes. We confirmed the previously proposed two-step expansion scenario from the Danube refuge, the existence of a secondary refuge (Western-Atlantic) during the last glaciation and population expansion of this lineage. Conspicuous divergences among Mediterranean populations reflect their different origin, as well as their low contribution to the recent genetic pool of chub in Central Europe.