Many freshwater gastropod species face extinction, including 79% of species in the family Pleuroceridae. The Oblong Rocksnail, Leptoxis compacta, is a narrow range endemic pleurocerid from the Cahaba River basin in central Alabama that has seen rapid range contraction in the last 100 years. Such a decline is expected to negatively affect genetic diversity in the species. However, precise patterns of genetic variation and gene flow across the restricted range of L. compacta are unknown. This lack of information limits our understanding of human impacts on the Cahaba River system and Pleuroceridae. Here, we show that L. compacta has likely seen a species-wide decline in genetic diversity, but remaining populations have relatively high genetic diversity. We also report a contemporary range extension compared to the last published survey. Leptoxis compacta does not display an isolation by distance pattern, contrasting patterns seen in many riverine taxa. Our findings also indicate that historical range contraction has resulted in the absence of common genetic patterns seen in many riverine taxa like isolation by distance as the small distribution of L. compacta allows for relatively unrestricted gene flow across its remaining range despite limited dispersal abilities. Two collection sites had higher genetic diversity than others, and broodstock sites for future captive propagation and reintroduction efforts should utilize sites identified here as having the highest genetic diversity. Broadly, our results support the hypothesis that range contraction will result in the reduction of species-wide genetic diversity, and common riverscape genetic patterns cannot be assumed to be present in species facing extinction risk.

中文翻译：

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长方形岩钉鼠（Leptoxis compacta）的范围缩小，塑造了河景的遗传模式

许多淡水腹足动物物种面临灭绝，其中包括芦苇科的79％。长方形长钉蜗牛Leptoxis compacta是来自阿拉巴马州中部Cahaba河盆地的一种窄范围特有的胸膜胃癌，在过去100年中出现了快速范围的收缩。预计这种下降会对物种的遗传多样性产生负面影响。但是，在紧凑型乳杆菌的有限范围内，遗传变异和基因流的精确模式是未知的。信息的缺乏限制了我们对人类对卡哈巴河水系和侧耳科的影响的理解。在这里，我们展示了L. compacta可能已经看到全物种的遗传多样性下降，但其余种群的遗传多样性却相对较高。与上次发布的调查相比，我们还报告了当代范围的扩展。Leptoxis compacta并没有显示出距离模式的隔离，这与许多河流生物分类中的模式形成了鲜明对比。我们的发现还表明，历史范围的缩小导致缺乏许多河流分类群中常见的遗传模式，例如通过距离隔离以及紧凑型乳杆菌的小距离分布。尽管分散能力有限，但允许在其剩余范围内相对不受限制地流动基因。两个收集地点的遗传多样性高于其他收集地点，亲虾地点用于未来的圈养繁殖和再引入工作应利用此处确定的遗传多样性最高的地点。从广义上讲，我们的结果支持以下假设：范围缩小将导致物种范围内的遗传多样性减少，并且不能假定常见的河景遗传模式存在于面临灭绝风险的物种中。