Introgression and niche dynamics in two ecologically divergent species

物种范围的边缘在气候变化下可能是最脆弱的，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)两个密切相关但在生态上截然不同的悬钩子物种(棕榈悬钩子和灰悬钩子)在距离漂移及其后果以及过去的气候变化方面的差异，以及(2)这两个物种在接触区的不对称入渗。我们研究了来自两个物种南缘和北缘的9个种群。基于12个假定的功能基因序列的联合分析，结合GLM期间的生态位模拟，表明最南端的棕榈鼠种群可能从最后一次冰盛期(LGM)之前就存在了。相反，灰熊种群的分化相对较近，可能代表了向北迁移的年轻前哨。只有在雅库什岛上的棕榈大头鱼和灰大头大头鱼之间才检测到显著的入侵，那里物种的范围边缘在热带附近重叠。对岛上接触带10个种群的结构分析表明，沿海拔呈渐进式递进。进一步的调查正在进行中，以测试是否有任何正在选择的基因在从一个物种转移到另一个物种的速度快于中性预期。我们得出的结论是，在这些由气候变化引起的边缘种群中，最近发生了这些亲缘关系之间的渗透。在极端环境下，在物种的生态位中，导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.