Data from: Tales of the unexpected: Phylogeography of the arctic-alpine model plant Saxifraga oppositifolia (Saxifragaceae) revisited

Arctic-alpine biota occupy enormous areas in the Arctic and the northern hemisphere mountain ranges, and have undergone major range shifts during their comparatively short history. The origins of individual arctic-alpine species remain largely unknown. In the case of the Purple saxifrage, Saxifraga oppositifolia, an important model for arctic-alpine plants, phylogeographic studies have remained inconclusive about early stages of the species’ spatiotemporal diversification, but have provided evidence for long-range colonization out of a presumed Beringian origin to cover today's circumpolar range. . We re-evaluated the species’ large-scale range dynamics based on a geographically extended sampling including crucial areas such as Central Asia and the (south-)eastern European mountain ranges and employing up-to-date phylogeographic analyses of a plastid sequence and a more restricted AFLP data set. In accordance with previous studies, we detected two major plastid DNA lineages also reflected in AFLP divergence, suggesting a long and independent vicariant history. Although we were unable to determine the species’ area of origin, our results point to the Alps and probably Central Asia, respectively, as the likely ancestral areas of the two main clades. AFLP data suggested that contact areas between the two clades in Eastern Europe, Northern Siberia and Greenland were secondary. In marked contrast to high levels of diversity revealed in previous studies, populations from the major arctic refugium Beringia did not exhibit any plastid sequence polymorphism. Our study shows that adequate sampling of the southern, refugial populations is crucial for understanding the range dynamics of arctic-alpine species.

北极高山生物群（Arctic-alpine biota）占据了北极及北半球山地的广袤区域，在其相对短暂的演化历史中经历了大范围的分布区变迁。目前学界对多数北极高山物种的起源仍知之甚少。以北极高山植物的重要模式物种——对叶虎耳草（Saxifraga oppositifolia）为例，现有系统地理学研究对该物种时空分化的早期阶段尚未得出明确结论，但已有证据表明，其从推测的白令起源地发生长距离殖民，最终形成了如今的环北极分布格局。本研究通过扩大地理采样范围（涵盖中亚、（南）欧东部山地等关键区域），并采用质体序列及有限扩增片段长度多态性（AFLP）数据集的最新系统地理学分析方法，重新评估了该物种的大范围分布动态。与既往研究结果一致，本研究检测到两大质体DNA谱系，该分化也在AFLP数据中有所体现，表明二者经历了漫长且独立的异域分化历程。尽管本研究未能确定该物种的起源地，但结果显示两大主要演化支的祖先分布区分别为阿尔卑斯山与中亚（大概率）。AFLP数据表明，两大演化支在东欧、北西伯利亚及格陵兰的接触区为次生接触带。与既往研究中检测到的高水平遗传多样性形成鲜明对比的是，主要北极避难所白令陆桥区域的种群未表现出任何质体序列多态性。本研究表明，对南部避难所种群的充分采样，是理解北极高山物种分布动态的关键。