Abstract
Pleistocene climatic changes affected the current distribution and genetic structure of alpine plants. Some refugial areas for the high elevation species have been proposed in the Alps, but whether they could survive on nunataks, is still controversial. Here, the spatial genetic structure in Salix serpillifolia revealed by chloroplast (cpSSR) and nuclear (nSSR) microsatellites was compared with the MaxEnt-modelled geographic distributions under current and past (Last Glacial Maximum) climate conditions. Our results suggest that the genetic pattern of differentiation detected in S. serpillifolia may be explained by the existence of Pleistocene refugia, including nunataks. The geographical patterns of variation obtained from the chloroplast and nuclear markers were not fully congruent. The spatial genetic structure that was based on nSSRs was more homogenous, while the cpSSR-based pattern pointed at strong genetic structure along the Alps. Five populations from the Central Alps had a combination of local and unique cpSSR clusters and admixture of those occurring in the Western and Eastern Alps. These findings may indicate the local survival of small populations of S. serpillifolia that were subsequently populated by new colonists in the postglacial period.
Highlights
Quaternary climate oscillations have caused entire plant zones to shift (Huntley and Birks 1983; Comes and Kadereit 1998; Tzedakis et al 2013)
Detailed information on the polymorphisms of the nSSR loci that were used in this study is presented in Online Resource 1
Our study shows that S. serpillifolia harbours moderate genetic and allelic diversity at nuclear microsatellites (HE = 0.644; A = 10.933; at the species level, not presented in the results section), yet this diversity was comparable to previously observed estimations in the arctic-alpine willow species, S. lanata, S. lapponum and S. herbacea (HE = 0.706, 0.703, 0.527; A = 8.4, 12.4, 5.8, respectively) (Stamati et al 2007)
Summary
Quaternary climate oscillations have caused entire plant zones to shift (Huntley and Birks 1983; Comes and Kadereit 1998; Tzedakis et al 2013). Cooling might have increased the area that was available to some species and allowed them to expand This is probably the case with some tundra plants, which had a larger range in the periglacial tundra than in the present period The relatively mild climate in the lowlands south of the Alps during the glacial periods allowed tree species to grow and persist but these conditions were likely not suitable for alpine species (Ravazzi 2002; Schönswetter et al 2005; Stewart et al 2010). Along with the expansion of the glaciers in the cold Quaternary phases, the habitats of the European high-mountain plants were becoming increasingly limited.
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