Hybridization is a key mechanism involved in lineage diversification and speciation, especially in ecosystems that experienced repeated environmental oscillations. Recently radiated plant groups, which have evolved in mountain ecosystems impacted by historical climate change provide an excellent model system for studying the impact of gene flow on speciation. We combined organellar (whole-plastome) and nuclear genomic data (RAD-seq) with a cytogenetic approach (rDNA FISH) to investigate the effects of hybridization and introgression on evolution and speciation in the genus Soldanella (snowbells, Primulaceae). Pervasive introgression has already occurred among ancestral lineages of snowbells and has persisted throughout the entire evolutionary history of the genus, regardless of the ecology, cytotype, or distribution range size of the affected species. The highest extent of introgression has been detected in the Carpathian species, which is also reflected in their extensive karyotype variation. Introgression occurred even between species with dysploid and euploid cytotypes, which were considered to be reproductively isolated. The magnitude of introgression detected in snowbells is unprecedented in other mountain genera of the European Alpine System investigated hitherto. Our study stresses the prominent evolutionary role of hybridization in facilitating speciation and diversification on the one hand, but also enriching previously isolated genetic pools. [chloroplast capture; diversification; dysploidy; European Alpine system; introgression; nuclear-cytoplasmic discordance; ribosomal DNA.].

Center for Theoretical Study Charles University and the Academy of Sciences of the Czech Republic Jilská 1 110 00 Praha Czech Republic

Central European Institute of Technology Department of Experimental Biology Faculty of Science Masaryk University Kamenice 753 5 CZ 625 00 Brno Czech Republic

Department of Biology Ecology and Earth Sciences University of Calabria Rende Cosenza Italy

Department of Botany and Biodiversity Research University of Vienna Vienna Austria

Department of Botany Charles University Prague Czech Republic

Department of Evolution and Systematics Plant Science and Biodiversity Centre Slovak Academy of Sciences Institute of Botany Bratislava Slovakia

Department of Zoology Comenius University in Bratislava Bratislava Slovakia

Slovak National Museum Natural History Museum Bratislava Slovakia

Université Grenoble Alpes University of Savoie Mont Blanc CNRS Grenoble France

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