Ara Motia G, McCulloch Graham A, Dutoit Ludovic, Wallis Graham P, Ingram Travis
Department of Zoology University of Otago Dunedin New Zealand.
Department of Marine Fisheries and Oceanography Patuakhali Science and Technology University Patuakhali Bangladesh.
Ecol Evol. 2024 Feb 16;14(2):e10987. doi: 10.1002/ece3.10987. eCollection 2024 Feb.
Landlocking of diadromous fish in freshwater systems can have significant genomic consequences. For instance, the loss of the migratory life stage can dramatically reduce gene flow across populations, leading to increased genetic structuring and stronger effects of local adaptation. These genomic consequences have been well-studied in some mainland systems, but the evolutionary impacts of landlocking in island ecosystems are largely unknown. In this study, we used a genotyping-by-sequencing (GBS) approach to examine the evolutionary history of landlocking in common smelt () on Chatham Island, a small isolated oceanic island 800 kilometres east of mainland New Zealand. We examined the relationship between Chatham Island and mainland smelt and used coalescent analyses to test the number and timing of landlocking events on Chatham Island. Our genomic analysis, based on 21,135 SNPs across 169 individuals, revealed that the Chatham Island smelt was genomically distinct from the mainland New Zealand fish, consistent with a single ancestral colonisation event of Chatham Island in the Pleistocene. Significant genetic structure was also evident within the Chatham Island smelt, with a diadromous Chatham Island smelt group, along with three geographically structured landlocked groups. Coalescent demographic analysis supported three independent landlocking events, with this loss of diadromy significantly pre-dating human colonisation. Our results illustrate how landlocking of diadromous fish can occur repeatedly across a narrow spatial scale, and highlight a unique system to study the genomic basis of repeated adaptation.
淡水系统中洄游性鱼类的陆封现象会产生重大的基因组后果。例如，洄游生活阶段的丧失会显著减少种群间的基因流动，导致遗传结构增强以及局部适应性效应增强。这些基因组后果在一些大陆系统中已得到充分研究，但岛屿生态系统中陆封现象的进化影响在很大程度上尚不清楚。在本研究中，我们采用简化基因组测序（GBS）方法来研究查塔姆岛（位于新西兰大陆以东800公里处的一个孤立的小海洋岛屿）上普通胡瓜鱼（）陆封现象的进化历史。我们研究了查塔姆岛胡瓜鱼与大陆胡瓜鱼之间的关系，并使用溯祖分析来检验查塔姆岛陆封事件的数量和时间。我们基于169个个体的21,135个单核苷酸多态性（SNP）进行的基因组分析表明，查塔姆岛胡瓜鱼在基因组上与新西兰大陆的鱼类不同，这与更新世时期查塔姆岛的单次祖先殖民事件一致。查塔姆岛胡瓜鱼内部也存在显著的遗传结构，有一个洄游型查塔姆岛胡瓜鱼群体，以及三个地理结构上的陆封群体。溯祖种群动态分析支持了三次独立的陆封事件，这种洄游性的丧失明显早于人类殖民。我们的结果说明了洄游性鱼类的陆封现象如何能在狭窄的空间尺度上反复发生，并突出了一个研究反复适应的基因组基础的独特系统。
