Format: ORAL

Loi¨c Pittet1, Natascha Wagner1, Pia Marinc?ek1, Elvira Ho¨randl1

1. Department of Systematic Botany, University of Göttingen, Germany

The geographic distribution of genetic lineages is highly impacted by climate fluctuations. Cold-adapted plant species have survived the last glaciations on nunataks within the glaciated area of the European Alps, unglaciated areas at the periphery of the ice sheet, in the marginal lowlands, or in other mountains of the European Alpine Systems that have been less glaciated. Following the last glacial period, cold-adapted species started to spread to newly available areas. The colonization is influenced by species-specific factors as well as evolutionary processes like hybridization and is still on-going. Two closely related but previously isolated species that merge their marginal ranges during recolonization create a secondary contact zone where hybridization can occur and potentially block the recolonization. Using Restriction-Site-Associated DNA sequencing, morphometrics, species distribution modelling and fine-grained environmental data, we aim to identify potential glacial refugia and recolonization routes of two willow (Salix L.) sister species pairs that show vicariant distributions and secondary contacts in the European Alps. We aim to characterize the hybrid zones genetically, morphologically, and ecologically to test the hypothesis that hybrid zones influence biogeographical patterns of parent species. Different potential glacial refugia were found in the southern European mountain systems or alpine periphery and suggest recolonization of the Alps from both eastern and western marginal areas. Hybrid zones show patterns of introgression rather than hybrid speciation and extend over several hundred kilometers. A discrepancy between phenotype and genotype could have resulted from backcrossing and segregation of later generation hybrids. Suitable environmental conditions were found for each species beyond their current distributions. Ecological relevees of secondary contact zones indicate high ecological niche similarity with parents but also niche expansion. No apparent reduction of fertility of hybrids was observed in the field. Altogether, our results support the hypothesis that hybrid zones can block the recolonization of parents.