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

杂交可以产生同倍体或多倍体杂交种，但也可以通过渐渗杂交在种间转移性状，并增加渐渗种的遗传变异。虎耳草组虎耳草亚组。蛛形纲有12种，生态和分布差异很大。其中2种主要分布在末次盛冰期冰川以外阿尔卑斯山脉以南和以东的低海拔地区，生长在钙质或非钙质岩石的荫蔽处；6种主要分布在末次盛冰期冰川内部或边缘的亚高山至高山海拔地区，生长在砾石、碎石或岩石上。其余四种表现出前两种的生态地理特征的马赛克，它们生长在阴凉的洼地中，但在很宽的海拔范围内，或只生长在高海拔地区，或生长在很宽的海拔范围内的岩石上。此外，该分部的12种中有7种或多或少是狭窄的地方性物种，只有5种占据更大的地理范围。该分部的质体和核系统发育的比较揭示了系统发育拓扑结构的支持冲突，这可能意味着物种之间的杂交。在此背景下，本研究的主要目的是研究具有马赛克生态地理特性的物种和具有广泛地理分布的物种是否分别显示了过去杂交的证据，这种杂交可能导致适应性性状的转移或遗传变异的增加，从而促进了范围的扩大。作为第一步，我们打算使用杂交捕获方法重建该分段的物种树，并通过聚结模拟揭示可能的过去杂交。利用生态指标值对物种生态位进行表征，重构群落生态位演化和祖先区。物种树中生态位转移/范围扩展与杂交的一致性将首次为杂交在群落生态位和分布区域演化中可能发挥的作用提供证据。

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.