Higher genetic diversity on mountain tops: the role of historical and contemporary processes in shaping genetic variation in the bank vole

Abstract

Glacial phases during the Pleistocene caused remarkable changes in species range distributions, with inevitable genetic consequences. Specifically, during interglacial phases, when the ice melted and new habitats became suitable again, species could recolonize regions that were previously covered by ice, such as high latitudes and elevations. Based on theoretical models and empirical data, a decrease in genetic variation is predicted along recolonization routes as a result of the consecutive founder effects that characterize the recolonization process. In the present study, we assessed the relative importance of historical and contemporary processes in shaping genetic diversity and differentiation of bank vole (Myodes glareolus) populations at different elevations in the Swiss Alps. By contrast to expectations, we found that genetic variation increased with elevation. Estimates of recent migration rates and a contrasting pattern of genetic differentiation observed at the mitochondrial cytochrome b gene and nuclear microsatellites support the hypothesis that higher genetic diversity at high elevation results from contemporary gene flow. Although historical recolonization processes can have marked effects on the genetic structure of populations, the present study provides an example where contemporary processes along an environmental gradient can reverse predicted patterns of genetic variation.

Small‐scale spatial variation in infection risk shapes the evolution of a Borrelia resistance gene in wild rodents

“…Alternatively, the formation or introgression of TLR2 c4 could be recent and local (see also above) and given the relatively low dispersal capability of voles (Le Galliard, Rémy, Ims, & Lambin, ), it might take a long time for the variant to spread to other populations. Indeed, small but significant population differentiation at neutral genetic markers has been observed among all our study populations, even among populations within the same valley (Cornetti et al., ), providing support that gene flow among populations is limited. Whereas reduced gene flow may explain why the variant is present in some valleys but not in others, importantly within valleys gene flow is higher (rather than lower) at high‐elevation sites (Cornetti et al., ).…”

“…Indeed, small but significant population differentiation at neutral genetic markers has been observed among all our study populations, even among populations within the same valley (Cornetti et al., ), providing support that gene flow among populations is limited. Whereas reduced gene flow may explain why the variant is present in some valleys but not in others, importantly within valleys gene flow is higher (rather than lower) at high‐elevation sites (Cornetti et al., ). The low frequency of TLR2 c4 at higher elevations thus cannot be explained by reduced gene flow at these sites.…”

“…Instead, a variant that has previously only been reported from the Italian bank vole lineage (TLR2 c4 ; Morger et al, 2015) was associated with a lower likelihood of Borrelia infection in our study populations. This is remarkable because bank voles at our study sites belong to the Western lineage (Cornetti et al, 2016), which has been separated from the Italian lineage >0.27 Ma (Deffontaine et al, 2005). It suggests either that TLR2 c4 is evolutionarily old (i.e., its origin pre-dates the split of the Western and Italian bank vole lineages) but has been lost from most other European populations (Morger et al, 2015), that TLR2 c4 has been introduced into our populations through immigrants from the Italian clade, or that pathogen-mediated selection has favoured the formation and spread of a new protective variant (TLR2 c4 ) after TLR2 c2 has been lost through neutral processes, such as bottlenecks and drift (i.e., independent convergent evolution in populations of the Western and Italian clades).…”

Bank Voles in Southern Eurasia: Vicariance and Adaptation

“…Several Alpine localities of the Western lineage exhibited a congruent divergence in tooth shape and climatic conditions. This echoes the recent finding of a high genetic diversity and important small-scale geographic structure in Alpine bank voles (Cornetti et al 2016). The mountainous landscape likely promotes extreme climatic differences even over a short geographic distance, and the topography may constitute barriers to gene flow.…”

Temporal environmental variation imposes differential selection on genomic and ecological traits of virtual plant communities

“…Since variation in our experiments could be increased neither by mutation 476 (Josephs et al 2017), nor by external gene flow (Cornetti et al 2016), selection 477 could only act on standing variation. Under these conditions, a higher linkage 478 of genes preserves variation in the associated trait (cf.…”