Abstract
Pleistocene glaciations dramatically affected species distribution in regions that were impacted by ice cover and subsequent postglacial range expansion impacted contemporary biodiversity in complex ways. The European whitefish, Coregonus lavaretus, is a widely distributed salmonid fish species on mainland Europe, but in Britain it has only seven native populations, all of which are found on the western extremes of the island. The origins and colonization routes of the species into Britain are unknown but likely contributed to contemporary genetic patterns and regional uniqueness. Here, we used up to 25,751 genome‐wide polymorphic loci to reconstruct the history and to discern the demographic and evolutionary forces underpinning divergence between British populations. Overall, we found lower genetic diversity in Scottish populations but high differentiation (F ST = 0.433–0.712) from the English/Welsh and other European populations. Differentiation was elevated genome‐wide rather than in particular genomic regions. Demographic modelling supported a postglacial colonization into western Scotland from northern refugia and a separate colonization route for the English/Welsh populations from southern refugia, with these two groups having been separated for more than ca. 50 Ky. We found cyto‐nuclear discordance at a European scale, with the Scottish populations clustering closely with Baltic population in the mtDNA analysis but not in the nuclear data, and with the Norwegian and Alpine populations displaying the same mtDNA haplotype but being distantly related in the nuclear tree. These findings suggest that neutral processes, primarily drift and regionally distinct pre‐glacial evolutionary histories, are important drivers of genomic divergence in British populations of European whitefish. This sheds new light on the establishment of the native British freshwater fauna after the last glacial maximum.
Highlights
Understanding the demographic and evolutionary forces shaping differentiation and speciation is a major undertaking in evolutionary biology (Seehausen et al, 2014)
This is relevant for determining historical processes, and to generate critical contemporary knowledge on how species are structured across their range, information that is important for conservation (Funk et al, 2012)
We obtained a total of 102 C. lavaretus samples from 11 populations from across Eurasia (Figure 1): 10 individuals from Koppentraun in the Alpine region in Austria (ALP), 10 individuals from Achterwasser in the Baltic region in Germany (BAL), 10 individuals from Lake Hávgajávri in Norway (NOR), 4 individuals from the River Ob in Russia (RUS), 10 individuals from Loch Lomond (LOM) and from Loch Eck (ECK) in Scotland, individuals from Llyn Tegid in Wales (LTE), and from England, 11 individuals from Red Tarn (RTA), 4 individuals from Haweswater (HAW), 11 individuals from Ullswater (UWA) and 11 individuals from Brotherswater (BWA)
Summary
Understanding the demographic and evolutionary forces shaping differentiation and speciation is a major undertaking in evolutionary biology (Seehausen et al, 2014). Some contradictions exist between these different data types, they generally suggest a separation between populations in Scotland, Wales and England, with the Welsh population being more closely related to the English populations These studies have lacked contextualization by continental Europe populations and were based on few genetic markers, and it was not possible to infer the drivers of differentiation, the role of complex postglacial demography, and whether major genomic structural differences are involved. To infer the role of particular genomic regions in divergence, we investigate genome- wide differentiation and admixture amongst populations These results shed new light on the establishment of the native British freshwater fauna after the last glacial maximum and highlight the
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