Mimura Makiko, Mishima Misako, Lascoux Martin, Yahara Tetsukazu
BMC Evol Biol. 2014 Oct 25;2014:209. doi: 10.1186/s12862-014-0209-9.
The margins of a species' range might be located at the margins of a species' niche, and in such cases, can be highly vulnerable to climate changes. They, however, may also undergo significant evolutionary changes due to drastic population dynamics in response to climate changes, which may increase the chances of isolation and contact among species. Such species interactions induced by climate changes could then regulate or facilitate further responses to climatic changes. We hypothesized that climate changes lead to species contacts and subsequent genetic exchanges due to differences in population dynamics at the species boundaries. We sampled two closely related Rubus species, one temperate (Rubus palmatus) and the other subtropical (R. grayanus) near their joint species boundaries in southern Japan. Coalescent analysis, based on molecular data and ecological niche modelling during the Last Glacial Maximum (LGM), were used to infer past population dynamics. At the contact zones on Yakushima (Yaku Island), where the two species are parapatrically distributed, we tested hybridization along altitudinal gradients.
Coalescent analysis suggested that the southernmost populations of R. palmatus predated the LGM (~20,000 ya). Conversely, populations at the current northern limit of R. grayanus diverged relatively recently and likely represent young outposts of a northbound range shift. These population dynamics were partly supported by the ensemble forecasting of six different species distribution models. Both past and ongoing hybridizations were detected near and on Yakushima. Backcrosses and advanced-generation hybrids likely generated the clinal hybrid zones along altitudinal gradients on the island where the two species are currently parapatrically distributed.
Climate oscillations during the Quaternary Period and the response of a species in range shifts likely led to repeated contacts with the gene pools of ecologically distinct relatives. Such species interactions, induced by climate changes, may bring new genetic material to the marginal populations where species tend to experience more extreme climatic conditions at the margins of the species distribution.
一个物种分布范围的边缘可能位于其生态位的边缘，在这种情况下，极易受到气候变化的影响。然而，由于应对气候变化时剧烈的种群动态变化，它们也可能经历显著的进化改变，这可能增加物种间隔离和接触的机会。气候变化引发的这种物种相互作用进而可能调节或促进对气候变化的进一步响应。我们假设，由于物种边界处种群动态的差异，气候变化导致物种接触以及随后的基因交换。我们在日本南部两个近缘悬钩子属物种（一个为温带物种掌叶悬钩子（Rubus palmatus），另一个为亚热带物种灰白毛莓（R. grayanus））的联合物种边界附近进行了采样。基于分子数据和末次盛冰期（LGM）期间的生态位建模，采用溯祖分析来推断过去的种群动态。在屋久岛（Yaku Island）的接触带，这两个物种呈邻域分布，我们沿着海拔梯度测试了杂交情况。
溯祖分析表明，掌叶悬钩子最南端的种群早于末次盛冰期（约20,000年前）就已存在。相反，灰白毛莓当前北界的种群分化相对较晚，可能代表向北范围扩张的年轻前沿种群。六种不同物种分布模型的集合预测部分支持了这些种群动态。在屋久岛及其附近检测到了过去和正在进行的杂交现象。回交和高代杂种可能在该岛沿着海拔梯度形成了渐变杂交带，目前这两个物种在该岛呈邻域分布。
第四纪时期的气候振荡以及物种在范围扩张中的响应可能导致与生态上不同的近缘物种的基因库反复接触。气候变化引发的这种物种相互作用可能会给边缘种群带来新的遗传物质，在物种分布边缘，这些种群往往会经历更极端的气候条件。
