Two Cases of Ice-Age speciation in and Around the Alps

Sandra Gruenig, Ph.D

Department of Biology, University of Fribourg

Quaternary climatic oscillations in the European Alps provide a great system to study underpinnings of plant diversification. In particular, climate-induced range shifts, leading to allopatric differentiation and  secondary gene flow, likely promoted hybrid speciation and the emergence of new polyploid species. This talk will present two cases of Ice-Age-driven speciation in and around the Alps, in which hybridization and whole-genome duplication (WGD) underlie the origin of new species in response to glacial cycles.

In the first case, population genetics and climatic niche modeling were used to infer the hybrid origin of Pulmonaria helvetica, a narrow endemic species found in Western Switzerland, which was covered by ice during the Last Glacial Maximum (ca 22,000 years ago). The second case focuses on Biscutella laevigata, a textbook example of mixed-ploidy species complex in the Alps. By integrating spatial genetics, coalescent modeling, and climatic niche analyses, the evolutionary history of diploids and tetraploids was inferred, highlighting a considerable postglacial expansion of the tetraploids to their current distribution across the Alps. To test to which extant the expansion of autotetraploids was driven by adaptation to environmental heterogeneity, whole-genome sequences of selected pairs of diploid and tetraploid populations from lowland vs alpine environments in a factorial design were used, highlighting genomic signatures of adaptation to elevation in both diploids and autotetraploids. Finally, the role of WGD per se from post-polyploidy evolution on various phenotypes and their plasticity were disentangled by producing and manipulating synthetic tetraploids in two treatments corresponding to either standard or stressful conditions, highlighting contrasted long-term actions of selection on WGD-induced changes.