Environmental gradients between marine biogeographical provinces separate distinct faunal communities. However, the absence of absolute dispersal barriers allows numerous species to occur on both sides of such boundaries. While the regional populations of such widespread species are often morphologically indistinguishable from each other, genetic evidence suggests that they represent unique ecotypes, and likely even cryptic species, that may be uniquely adapted to their local environment. Here, we explored genomic divergence in four sympatric southern African decapod crustaceans whose ranges span the boundary between the cool-temperate west coast (south-eastern Atlantic) and the warm-temperate south coast (south-western Indian Ocean) near the southern tip of the African continent. Using genome-wide data, we found that all four species comprise distinct west coast and south coast ecotypes, with molecular dating suggesting divergence during the Pleistocene. Transcriptomic data from the hepatopancreas of twelve specimens of one of these species, the mudprawn Upogebia africana, which were exposed to either 10 °C or 20 °C, showed a clear difference in gene expression profiles between the west- and south coast ecotypes. This difference was particularly clear at 10 °C, where individuals from the south coast experienced a ‘transcriptomic shock’. This low temperature is more typical of the west coast during upwelling events, and the physiological stress experienced by the south coast ecotype under such conditions may explain its absence from that coastline. Our results shed new light on the processes involved in driving genomic divergence and incipient speciation along coastlines with porous dispersal barriers.

海洋生物地理省之间的环境梯度将不同的动物群落分开。然而，由于没有绝对的传播障碍，因此在边界两侧出现了大量物种。虽然这种分布广泛的物种的区域种群在形态上通常无法区分，但遗传证据表明它们代表了独特的生态型，甚至可能是隐蔽的物种，可能独特地适应了当地的环境。在这里，我们探索了四种同域南部非洲十足目甲壳类动物的基因组差异，它们的范围跨越了冷温带西海岸（东南大西洋）和南端附近的暖温带南海岸（西南印度洋）之间的边界。非洲大陆。使用全基因组数据，我们发现所有四个物种都包含不同的西海岸和南海岸生态型，分子测年表明更新世期间存在分歧。来自这些物种之一的十二个标本的肝胰腺的转录组学数据，泥虾暴露于 10 °C 或 20 °C 的Upogebia Africana显示出西海岸和南海岸生态型之间基因表达谱的明显差异。这种差异在 10 °C 时尤为明显，来自南海岸的个体经历了“转录组休克”。在上升流事件期间，这种低温在西海岸更为典型，而南海岸生态型在这种条件下所经历的生理压力可能解释了它不存在于该海岸线的原因。我们的结果为沿着具有多孔扩散屏障的海岸线驱动基因组分化和早期物种形成所涉及的过程提供了新的启示。