Data from: Post-glacial habitat release and incipient speciation in the genus Delphinus

The role of ecological and changing environmental factors in the radiation of species diversity is a fundamental question in evolutionary biology. Of particular interest is the potential for these factors to determine the boundary between what we would consider differentiation among populations, and incipient speciation. Dolphins in the genus Delphinus provide a useful test case, exhibiting morphological variation in beak length, colouration and body size across their wide geographic distribution, and in particular among coastal and more pelagic habitats. Two species have been proposed, D. delphis and D. capensis, but morphologically similar allopatric populations are not monophyletic, indicating that the mostly coastal ‘long-beaked’ D. capensis form is not a single globally distributed species. However, the sympatric populations in the Eastern North Pacific currently designated as these two species are both morphologically and genetically differentiated. Here we use microsatellite DNA and mtDNA markers to investigate the evolutionary mechanisms that led to this incipient speciation event. We used coalescent and assignment methods to investigate the timing and extent of reproductive isolation. Our data indicate that while there is some level of on-going gene flow, the putative species found in the Eastern North Pacific are reciprocally monophyletic. The timing of isolation appears to be associated with regional changes in paleoceanographic conditions within the Holocene timeframe.生态与动态环境因子在物种多样性辐射演化中的作用，是进化生物学领域的核心科学问题。其中尤为值得关注的是，这类因子或可划定种群分化与初期物种形成之间的界限。真海豚属（Delphinus）的海豚是理想的研究模型类群：它们在广泛的地理分布范围内，尤其是在近岸与远海生境之间，展现出喙长、体色与体型的形态变异。此前已有研究提出该属包含两个物种，即D. delphis与D. capensis，但形态相似的异域种群并非单系群（monophyletic），这表明主要栖息于近岸的“长喙”型D. capensis并非单一广布物种。不过，东太平洋东部目前被归为这两个物种的同域种群，却在形态与遗传层面均存在分化。本研究利用微卫星DNA（microsatellite DNA）与线粒体DNA（mtDNA）分子标记，探究导致该初期物种形成事件的进化机制；通过溯祖（coalescent）与种群指派分析方法，解析生殖隔离的形成时间与程度。研究结果显示，尽管存在一定程度的持续基因交流，但东太平洋东部的这两个推定物种互为单系群（monophyletic）。隔离事件的发生时间，似乎与全新世（Holocene）时期区域古海洋环境的变化存在关联。