Quaternary range shifts, hybridization and ecological niche evolution in Saxifraga sect. Saxifraga subsect. Arachnoideae

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Hybridization can result in either homoploid or polyploid hybrid species, but also, through introgressive hybridization, in the transfer of traits among species and in increased genetic variation in introgressed species. Saxifraga sect. Saxifraga subsect. Arachnoideae contains 12 species of widely divergent ecology and distribution. Whereas two species of the group are distributed at low altitudes south and east of the Alps outside the Last Glacial Maximum glaciers where they grow in shady recesses of calcareous or non-calcareous rocks, six are distributed at mostly subalpine to alpine altitudes inside or on the edge of the Last Glacial Maximum glaciers and grow on gravel, scree or rocks. The remaining four species show a mosaic of the ecogeographical properties of the preceding two groups by growing in shady recesses but across either a wide altitudinal range or at high altitudes only or by growing on rocks across a wide altitudinal range. Also, seven of the twelve species of the subsection are more or less narrow endemics and only five occupy wider geographical ranges. Comparison of plastid- and nuclear-based phylogenies of the subsection revealed supported conflict in phylogenetic topology which may imply hybridization between species. On this background, the major aim of the proposed project is to investigate whether the species with mosaic ecogeographical properties on the one hand and the species with wide geographical distributions on the other hand show evidence for past hybridization which may have led to the transfer of adaptive traits or to an increase of genetic variation facilitating range expansion, respectively. As a first step, we intend to reconstruct a species tree of the subsection using a hybrid capture approach, and to reveal possible past hybridization by coalescent simulations. Species niches will be characterized using ecological indicator values, and niche evolution and ancestral areas will be reconstructed for the study group. Coincidence in the species tree of niche shifts/range expansions and hybridization will provide first evidence for a possible role of hybridization in the evolution of ecological niche and distribution area in the study group.