Introgression and niche dynamics in two ecologically divergent species

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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.