Manuzzi et al_Population genomics and phylogeography of a benthic coastal shark (Scyliorhinus canicula) using 2b-RAD SNPs

The existence of strong genetic structure is expected in species with limited ability to disperse and philopatric behaviour. These life-history traits are found in many small benthic elasmobranchs, such as in the small-spotted catshark (Scyliorhinus canicula). However, no evidence of genetic structure was found across its northeastern Atlantic (NEA) range using traditional molecular markers. Here, fine-scale genetic differentiation was detected between the British Isles and southern Iberia using 2674 single nucleotide polymorphism loci generated using 2b-Restriction site Associated DNA (2b-RAD). Geographical distance and historical demography were two major drivers shaping the distribution of genetic diversity of S. canicula along the NEA. Significant positive spatial autocorrelation of allelic frequencies was detected, with genetic differentiation generally increasing with geographical distance. However, marked genetic divergence of the Celtic Sea and South Portugal collections from their closest neighbours resulted in geographically constrained genetic breaks south of the British Isles and off southwestern Iberia. Historical demographic reconstruction of population pairs across these genetic breaks suggested a scenario of historical isolation before secondary contact, probably related to distinct northern and southern glacial refugia. These results provide new insights into the population structure of S. canicula along the NEA and serve as a reference for benthic elasmobranchs.

在具有有限扩散能力和亲缘性行为物种中，预期存在强烈的遗传结构。许多小型底栖软骨鱼，如小斑猫鲨（Scyliorhinus canicula），均展现出这些生命史特征。然而，利用传统分子标记，在其东北大西洋（NEA）范围内并未发现遗传结构的证据。本研究中，通过2b-Restriction site Associated DNA（2b-RAD）技术生成了2674个单核苷酸多态性位点，在英吉利群岛与南伊比利亚之间检测到了精细的遗传分化。地理距离和历史人口统计是塑造S. canicula在NEA遗传多样性分布的两个主要驱动力。等位基因频率的空间自相关性显著，且遗传分化通常随着地理距离的增加而增强。然而，凯尔特海和南葡萄牙的样本与邻近地区之间显著的遗传差异，导致了不列颠群岛南部和伊比利亚西南部以南的地理限制性遗传断裂。对这些遗传断裂处人口对的历史人口统计重建，暗示了在次级接触之前的历史隔离情景，这可能与北部和南部的冰川避难所的差异性有关。这些研究结果为S. canicula在NEA的种群结构提供了新的见解，并为底栖软骨鱼的种群研究提供了参考。