ABSTRACT: The supralittoral zones of sandy beaches are particularly vulnerable to coastal development and other activities that cause localised habitat destruction. Supratidal species, such as peracarid crustaceans, which lack a pelagic larval phase and tend to avoid direct contact with the swash, are therefore expected to be distributed as isolated populations, with implications for their long-term survival. Genetic population structure of one such species, the pill bug Tylos capensis, was investigated based on mitochondrial cytochrome c oxidase subunit I (COI) haplotype sequences, to assess demographic history and regional population connectivity in the presence of potential dispersal barriers (an estuary, coastal cliffs) along the Indian Ocean coast of South Africa. Here, pill bugs demonstrated strong and significant genetic structure at the regional scale, with 3 distinct clades across the species’ geographic distribution. At a localised spatial scale, coastal cliffs intersecting the high shore appeared to be a strong barrier to gene flow between adjacent populations, while a permanently open estuary did not limit gene flow. Estimates of historic gene flow and patterns of COI differentiation coincided with greater habitat continuity during the Pleistocene glaciations at sea levels between -75 and -120 m, when the African south coast was probably dominated by sandy beaches. While gene flow among low-dispersing pill bug populations is unlikely to benefit from a network of closely spaced coastal protected areas, the isolated nature of this species, coupled with the cryptic diversity inherent in this taxon, emphasizes the need for their protection. The importance of protecting the intact littoral active zone of beaches is highlighted.

中文翻译：

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历史扩散障碍决定了潮上沙滩育雏器的遗传结构和连通性

摘要：沙滩上的沿海地带特别容易受到沿海开发和其他活动的影响，这些活动会导致局部栖息地破坏。因此，潮上物种，例如无远洋幼虫阶段并倾向于避免直接接触潮汐的甲壳类动物，预计将作为孤立的种群分布，从而影响它们的长期生存。基于线粒体细胞色素c研究了一种此类物种的遗传种群结构，药丸虫Tylos capensis氧化酶亚基 I (COI) 单倍型序列，以评估在南非印度洋沿岸存在潜在扩散障碍（河口、沿海悬崖）的情况下的人口历史和区域人口连通性。在这里，药丸虫在区域范围内表现出强大而显着的遗传结构，在该物种的地理分布中具有 3 个不同的进化枝。在局部空间尺度上，与高岸相交的海岸悬崖似乎是相邻种群之间基因流动的强大屏障，而永久开放的河口并没有限制基因流动。对历史基因流和 COI 分化模式的估计与更新世冰川期间 -75 至 -120 m 之间海平面的栖息地连续性更大，当时非洲南部海岸可能以沙滩为主。虽然低分散药丸虫种群之间的基因流动不太可能受益于紧密间隔的沿海保护区网络，但该物种的孤立性质，加上该分类群固有的神秘多样性，强调了对其保护的必要性。强调保护完整的沿海活动区海滩的重要性。