Abstract
In order to describe the influence of Pleistocene glaciations on the genetic structure and demography of a highly mobile, but specialized, passerine, the Savi’s Warbler (Locustella luscinioides), mitochondrial DNA sequences (ND2) and microsatellites were analysed in c.330 individuals of 17 breeding and two wintering populations. Phylogenetic, population genetics and coalescent methods were used to describe the genetic structure, determine the timing of the major splits and model the demography of populations. Savi’s Warblers split from its sister species c.8 million years ago and have two major haplotype groups that diverged in the early/middle Pleistocene. One of these clades originated in the Balkans and is currently widespread, showing strong evidence for population expansion; whereas the other is restricted to Iberia and remained stable. Microsatellites agreed with a genetic break around the Pyrenees, but showed considerable introgression and a weaker genetic structure. Both genetic markers showed an isolation-by-distance pattern associated with the population expansion of the eastern clade. Breeding populations seem to be segregated at the wintering sites, but results on migratory connectivity are preliminary. Savi’s Warbler is the only known migratory bird species in which Iberian birds did not expand beyond the Pyrenees after the last glaciation. Despite the long period of independent evolution of western and eastern populations, complete introgression occurred when these groups met in Iberia. Mitochondrial sequences indicated the existence of refugia-within-refugia in the Iberian Peninsula during the last glacial period, which is surprising given the high dispersal capacity of this species. Plumage differences of eastern subspecies seemed to have evolved recently through natural selection, in agreement with the glacial expansion hypothesis. This study supports the great importance of the Iberian Peninsula and its role for the conservation of genetic variation.
Highlights
Historic events, such as changes in climate and topography, have been shown to leave genetic signatures that subsist to the present time [1,2]
Mitochondrial DNA We analysed the complete (1041 bp) NADH dehydrogenase subunit 2 gene (ND2) gene of 330 individuals sampled from 17 breeding and two wintering sites, and included one sequence available in GenBank from Krasnodar, Russia [17]
Phylogeographic analysis has revealed common patterns in the genetic structure of numerous species, suggesting that at least some historical events were extremely influential at the community level [1,2,7]
Summary
Historic events, such as changes in climate and topography, have been shown to leave genetic signatures that subsist to the present time [1,2]. The quaternary glaciations, in particular, are thought to have been a major driving force of diversification and speciation, being the subject of multiple studies [3,4] During this period, most species have shown evidence for demographic and distributional changes (expansions and contractions) that seemed to occur in syntony with the advance and retreat of the ice sheets during the glacial cycles [5]. In Europe, three discrete major refugia were identified: the Iberian Peninsula, the Italian Peninsula and the Balkan region, which remained ice free and led to independent, allopatric evolution for considerable periods of time [1,2,6] Populations expanding from these refugia often met at suture (or hybrid) zones that are consistent across species, for instance at the Pyrenees and the Alps, across central Europe and across central Scandinavia [2]
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