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物种，但也可以通过渐进式杂交在物种之间转移性状，并在导入物种中增加遗传变异。Saxifraga学派虎耳草亚组。蛛网虫亚科有12种，生态和分布差异很大。其中两种分布在末次冰期最大冰川外阿尔卑斯山南部和东部的低海拔地区，生长在钙质或非钙质岩石的阴凉凹陷中，六种分布在末次冰期最大冰川内部或边缘的亚高山到高山高度，生长在砾石、碎石或岩石上。其余四个物种显示出前两个物种的生态地理特性的马赛克，它们生长在阴凉的凹处，但要么生长在宽海拔范围内，要么只生长在高海拔范围内，或者生长在宽海拔范围的岩石上。此外，小节中的12种中有7种或多或少是狭义的特有种，只有5种分布在更宽的地理范围内。对这一分段的基于叶绿体和基于核的系统发育进行比较，发现在系统发育拓扑上存在冲突，这可能意味着物种之间的杂交。在此背景下，该项目的主要目的是调查具有镶嵌生态地理属性的物种和具有广泛地理分布的物种是否分别显示出过去可能导致适应性状转移或有利于范围扩大的遗传变异的证据。作为第一步，我们打算使用混合捕获方法重建该分段的物种树，并通过合并模拟揭示可能的过去杂交。物种生态位将使用生态指标值进行表征，并将为研究组重建生态位进化和祖传区域。在生态位转移/范围扩展和杂交的物种树上的重合将为杂交在研究组生态位和分布区的进化中可能发挥的作用提供第一个证据。

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.