Colossendeis megalonyx Hoek, 1881 has the broadest distribution of all sea spiders in the Southern Ocean. Previous studies have detected several evolutionarily young lineages within this taxon and interpreted them as a result of allopatric speciation in a few shelf refuges during glacial maxima. However, alternative scenarios such as ecological speciation in sympatry have rarely been considered or tested. Here, we generated the most extensive genomic and morphometric data set on the C. megalonyx species complex to (i) comprehensively describe species diversity, (ii) explore intraspecific connectivity between populations located around Antarctica, and (iii) systematically test for positive selection indicative of adaptive speciation. We successfully applied a target hybrid enrichment approach and recovered all 1607 genes targeted. Phylogenomic analysis was consistent with previous findings and, moreover, increased the resolution of branching within lineages. We found specimens of phylogenetically well-separated lineages occurring in sympatry to be genetically distinct from each other and gene flow between geographically separated populations of the same lineages to be restricted. Evidence for positive selection was found for four genes associated with structural and neuronal functions. Hence, there is an indication for positive selection in the C. megalonyx species complex, yet its specific contribution to the speciation process remains to be explored further. Finally, morphometric analyses revealed multiple significant differences between lineages, but a clear separation proved difficult. Our study highlights the relevance of positive selection as a potential driver for speciation in the Southern Ocean.

中文翻译：

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使用海蜘蛛物种复杂 Colossendeis megalonyx 作为测试案例分析南大洋物种形成的驱动因素

Colossendeis megalonyx Hoek, 1881 是南大洋所有海蜘蛛中分布最广的。以前的研究已经在这个分类群中检测到了几个进化上年轻的谱系，​​并将它们解释为冰川最大值期间几个大陆架避难所中异域物种形成的结果。然而，很少考虑或测试替代方案，例如同情中的生态物种形成。在这里，我们在 C. megalonyx 物种复合体上生成了最广泛的基因组和形态测量数据集，以 (i) 全面描述物种多样性，(ii) 探索位于南极洲周围的种群之间的种内连通性，以及 (iii) 系统地测试阳性选择指示适应性物种形成。我们成功地应用了目标杂交富集方法并恢复了所有 1607 个目标基因。系统发育分析与之前的发现一致，而且增加了谱系内分支的分辨率。我们发现在系统发育上分离良好的谱系标本在基因上彼此不同，并且相同谱系的地理上分离的种群之间的基因流动受到限制。为与结构和神经元功能相关的四个基因发现了阳性选择的证据。因此，在 C. megalonyx 物种复合体中有阳性选择的迹象，但其对物种形成过程的具体贡献仍有待进一步探索。最后，形态计量学分析揭示了谱系之间的多个显着差异，但证明难以明确分离。