Centre for Ecological Genomics and Wildlife Conservation, Department of Zoology, University of Johannesburg, Auckland Park 2006, South Africa.
Hawai'i Institute of Marine Biology, University of Hawai'i at Mānoa, Kāne'ohe, Hawai'i, Honolulu, HI, USA.
Mar Genomics. 2021 Aug;58:100847. doi: 10.1016/j.margen.2021.100847. Epub 2021 Feb 24.
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.
环境梯度在海洋生物地理区之间分离出不同的动物群落。然而，没有绝对的扩散障碍使得许多物种能够出现在这些边界的两侧。虽然这些广泛分布的物种的区域种群在形态上彼此难以区分，但遗传证据表明它们代表独特的生态型，甚至可能是隐种，可能独特地适应其当地环境。在这里，我们探索了在南非的四种共生的十足甲壳动物中的基因组分歧，它们的范围跨越了非洲大陆南端附近的凉爽西海岸（东南大西洋）和温暖的南海岸（西南印度洋）之间的边界。使用全基因组数据，我们发现所有四个物种都包括独特的西海岸和南海岸生态型，分子年代学表明它们在更新世发生了分歧。对其中一种物种——泥虾 Upogebia africana 的 12 个标本的肝胰腺转录组数据进行分析，这些标本分别暴露在 10°C 或 20°C 下，显示出西海岸和南海岸生态型之间的基因表达谱有明显差异。这种差异在 10°C 时尤为明显，南海岸的个体经历了“转录组冲击”。这种低温在上升流事件期间更典型于西海岸，而南海岸生态型在这种条件下经历的生理压力可能解释了它在该海岸线上的缺失。我们的结果为驱动基因组分歧和沿扩散屏障海岸线发生初期物种形成的过程提供了新的见解。
