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, coloration 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 mitochondrial DNA 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 although 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之一。其中尤为受关注的是，这类因子能否界定种群分化与初期物种形成之间的分界阈值。真海豚属（Delphinus）物种便是极佳的研究案例：其地理分布范围极广，且在喙长、体色与体型上存在显著形态差异，尤其在近岸与远洋生境的种群间差异尤为突出。此前学界曾提出该属包含两个物种：真海豚（D. delphis）与长吻真海豚（D. capensis），但形态相似的异域种群并非单系群，这表明以近岸种群为主的‘长喙’型长吻真海豚并非单一的全球广布物种。但当前在北太平洋东部被划归为这两个物种的同域种群，却同时存在形态与遗传层面的分化。本研究利用微卫星DNA（microsatellite DNA）与线粒体DNA（mitochondrial DNA）分子标记，探究驱动这一初期物种形成事件的进化机制。我们采用溯祖分析与种群归属鉴定方法，解析生殖隔离的形成时间与隔离程度。研究数据显示：尽管存在一定程度的持续基因交流，但北太平洋东部的这两个推定物种互为单系群；而生殖隔离的形成时间，似乎与全新世时期区域古海洋环境的变化存在关联。