Introgression and niche dynamics in two ecologically divergent species

在气候变化的影响下，物种活动范围的边缘可能是最脆弱的，但由于剧烈的种群动态，例如与新物种的接触，它也可能经历重大的进化变化。我们测试了(1)两个密切相关但生态上截然不同的红颊草物种（R. palmatus和R. grayanus）的范围转移及其后果的差异，以及(2)这两个物种在接触区之间的不对称渗透。我们研究了两个物种南缘和北缘共9个居群。基于12个推测功能基因序列和生态位模型的聚结分析表明，掌纹草最南端的种群可能在末次盛冰期之前就存在了。相反，灰尾鼠种群分化相对较晚，可能代表了向北迁移的年轻前哨。在屋久岛，仅在掌鼠和灰鼠之间发现了显著的渐渗现象，其分布范围的边缘有明显的重叠。对岛上接触区10个种群的结构分析表明，沿海拔逐渐渗入。进一步的调查正在进行中，以测试是否有任何基因在选择中从一个物种转移到另一个物种的速度比中性预期更快。我们的结论是，在气候变化引起的这些边缘种群中，这些亲缘关系之间的渐渗最近发生了。在物种生态位的极端环境下，基因渗入可以增加物种范围边缘的进化潜力。

The margins of a species’ range might be most vulnerable under climate changes, but it may also undergo significant evolutionary change due to drastic population dynamics, e.g. contacts with new species. We tested(1) differences in range shift and its consequences, along with past climate change, in two closely related but ecologically distinct Rubus species (R. palmatus and R. grayanus) and(2) asymmetric introgression between these two species at the contact zone. We studied nine populations in total from southern and northern margins of two species. Coalescent analysis based on 12 putatively functional gene sequences together with niche modeling during GLM, suggested that the southernmost populations of R. palmatus perhaps persisted since before the Last Glacial Maximum (LGM). Conversely, the R. grayanuspopulations diverged relatively recently and likely represent young outposts of a northbound range shift. Significant introgression was only detected between R. palmatus and R. grayanus on Yakushima Island, where the margins of the species’ ranges overlapped parapatrically. Structure analysis in ten populations on the contact zone on the island suggests gradual introgression along the altitudes. Further investigation is in progress to test whether any gene under selection is moving from one to another species faster than neutral expectation. We conclude that introgression between these relatives has recently taken place at these marginal populations induced by climate changes. Introgression could increase the evolutionary potential at the margins of the species’ range under extreme environments in the species’ niches.