Phylogeography provides insights into how historical and contemporary processes influence the genetic structure and gene flow in marine organisms around the globe. In benthic marine invertebrates, a species’ reproductive strategy can strongly impact phylogeographic patterns and distribution, with some direct-developing (non-planktonic) dispersers demonstrating strong genetic structure but also broad geographic spread. While seemingly paradoxical, past work has shown ovoviviparous species, like Littorina saxatilis, can be more successful colonizers of remote locations than species with planktonic larvae, like L. littorea. Both Littorina species overlap in much of their North Atlantic ranges but have different colonization histories: L. saxatilis is native on both North Atlantic coasts and islands, and L. littorea is native to the eastern Atlantic but introduced to the west. Using an extensive mitochondrial dataset (1236 sequences; 85 sites), we examined how their opposing reproductive strategies correspond to their distributions and phylogeographies. Littorina saxatilis exhibited a heterogeneous genetic structure reflecting post-glacial recolonization from multiple refugial sites, while L. littorea had a homogeneous structure with a post-glacial history characterized by recolonization from one main refugial area in the northeast Atlantic. Further, haplotype diversity was significantly depressed in northwest Atlantic L. littorea populations, signifying a strong bottleneck characteristic of a human-mediated introduction. In contrast, haplotype diversity in L. saxatilis was similar between the two regions, demonstrating long-term history on both coasts. Thus, our study suggests contrasting life-history characteristics were a major structuring force in the phylogeographic patterns of these related species following large-scale disturbances (natural and anthropogenic) that compel contraction and redistribution over large areas.

系统地理学提供了对历史和当代过程如何影响全球海洋生物的遗传结构和基因流动的见解。在底栖海洋无脊椎动物中，物种的繁殖策略可以强烈影响系统地理学模式和分布，一些直接发育的（非浮游的）传播者表现出强大的遗传结构和广泛的地理分布。虽然看似自相矛盾，但过去的研究表明，卵胎生物种，如Littorina saxatilis，可能比L. littorea等具有浮游幼虫的物种更成功地定居在偏远地区。两种Littorina物种在北大西洋的大部分地区都有重叠，但有不同的殖民历史：L. saxatilisL. littorea原产于北大西洋沿岸和岛屿，L. littorea原产于东大西洋，但被引入西部。使用广泛的线粒体数据集（1236 个序列；85 个位点），我们检查了它们对立的繁殖策略如何与其分布和系统地理学相对应。Littorina saxatilis表现出异质的遗传结构，反映了来自多个避难所的冰川后重新殖民化，而L. littorea具有同质结构，具有冰河后历史，其特征是来自大西洋东北部一个主要避难所的重新殖民化。此外，西北大西洋L. littorea 的单倍型多样性显着降低种群，标志着人类介导的引入的强大瓶颈特征。相比之下，L. saxatilis 的单倍型多样性在两个地区之间相似，证明了两个海岸的长期历史。因此，我们的研究表明，在大规模干扰（自然和人为）迫使大面积收缩和重新分布之后，对比的生活史特征是这些相关物种系统地理学模式的主要结构力量。