Data from: Secondary contact and asymmetrical gene flow in a cosmopolitan marine fish across the Benguela upwelling zone

The combination of oceanographic barriers and habitat heterogeneity are known to reduce connectivity and leave specific genetic signatures in the demographic history of marine species. However, barriers to gene flow in the marine environment are almost never impermeable which inevitably allows secondary contact to occur. In this study eight sampling sites (five along the South African coastline, one each in Angola, Senegal and Portugal) were chosen to examine the population genetic structure and phylogeographic history of the cosmopolitan bluefish (Pomatomus saltatrix), distributed across a large South-east Atlantic upwelling zone. Bayesian clustering and FST analyses were applied to mtDNA cytochrome b, intron AM2B1 and 15 microsatellite loci. We detected uncharacteristically high genetic differentiation (FST 0.15-0.20; p<0.001) between the fish sampled from South Africa and the other sites, strongly influenced by five outlier microsatellite loci located in conserved intergenic regions. In addition, differentiation among the remaining East Atlantic sites was detected, although mtDNA indicated past isolation with subsequent secondary contact between these East Atlantic populations. We further identified secondary contact, with unidirectional gene flow from South Africa to Angola. The directional contact is likely explained by a combination of the northward flowing offshore current and endogenous incompatibilities restricting integration of certain regions of the genome and limiting gene flow to the south. The results confirm that the dynamic system associated with the Benguela Current upwelling zone influences species distributions and population processes in the South-east Atlantic.

众所周知，海洋学屏障与生境异质性的共同作用会降低种群连通性，并在海洋物种的种群历史中留下特定的遗传印记。然而，海洋环境中的基因流屏障几乎从不完全阻隔，这不可避免地会引发二次接触事件。本研究选取8个采样位点（南非海岸线沿线5个，安哥拉、塞内加尔及葡萄牙各1个），对广泛分布于东南大西洋大型上升流区的广布性扁鲹（Pomatomus saltatrix）的种群遗传结构与系统地理学历史展开研究。本研究针对线粒体DNA（mtDNA）细胞色素b、内含子AM2B1以及15个微卫星位点开展贝叶斯聚类与FST分析。研究检测到南非采样群体与其余位点的采样群体间存在异常高的遗传分化（FST值为0.15~0.20；p<0.001），这一结果主要受位于保守基因间区的5个异常微卫星位点影响。此外，本研究还检测到其余东大西洋采样位点间存在遗传分化；尽管线粒体DNA分析结果显示，这些东大西洋种群曾经历隔离，随后发生了二次接触。本研究进一步证实了二次接触事件的存在，其基因流呈现从南非流向安哥拉的单向性特征。这种定向的基因流模式可能由两方面因素共同导致：一是向北流动的离岸海流，二是内源不相容性会阻碍基因组特定区域的整合，并限制向南的基因流。本研究结果证实，与本格拉海流（Benguela Current）上升流区相关的动态海洋系统会对东南大西洋海域的物种分布与种群过程产生影响。