Data from: Spatiotemporal analysis of gene flow in Chesapeake Bay Diamondback Terrapins (Malaclemys terrapin)

There is widespread concern regarding the impacts of anthropogenic activities on connectivity among populations of plants and animals, and understanding how contemporary and historical processes shape metapopulation dynamics is crucial for setting appropriate conservation targets. We used genetic data to identify population clusters and quantify gene flow over historical and contemporary time frames in the Diamondback Terrapin (Malaclemys terrapin). This species has a long and complicated history with humans, including commercial over-harvesting and subsequent translocation events during the early twentieth century. Today, terrapins face threats from habitat loss and mortality in fisheries bycatch. To evaluate population structure and gene flow among Diamondback Terrapin populations in the Chesapeake Bay region, we sampled 617 individuals from 15 localities, and screened individuals at 12 polymorphic microsatellite loci. Our goals were to demarcate metapopulation structure, quantify genetic diversity, estimate effective population sizes, and document temporal changes in gene flow. We found that terrapins in the Chesapeake Bay region harbor high levels of genetic diversity and form four populations. Effective population sizes were variable. Among most population comparisons, estimates of historical and contemporary terrapin gene flow were generally low (m ≈ 0.01). However, we detected a substantial increase in contemporary gene flow into Chesapeake Bay from populations outside the bay, as well as between two populations within Chesapeake Bay, possibly as a consequence of translocations during the early twentieth century. Our study shows that inferences across multiple time scales are needed to evaluate population connectivity, especially as recent changes may identify threats to population persistence.当前，人类活动对动植物种群间连通性的负面影响已引发广泛关注；厘清当代与历史演化过程如何塑造集合种群（metapopulation）动态，对于制定合理的保护目标至关重要。本研究以钻纹龟（Diamondback Terrapin，学名Malaclemys terrapin）为研究对象，利用遗传数据识别其种群聚类单元，并量化历史与当代时间尺度下的基因流（gene flow）。该物种与人类的交互历史悠久且复杂，包括20世纪早期的商业性过度捕捞及后续的人为移殖事件。如今，钻纹龟面临栖息地丧失与渔业兼捕致死的多重生存威胁。为探究切萨皮克湾区域钻纹龟种群的遗传结构与基因流模式，本研究从15个采样位点共采集617个个体样本，并对12个多态性微卫星位点进行基因分型筛查。本研究的核心目标包括：划定集合种群结构、量化遗传多样性水平、估算有效种群大小，以及记录基因流的时间动态变化。研究结果显示，切萨皮克湾区域的钻纹龟群体具有较高的遗传多样性，可划分为4个种群。有效种群大小存在显著异质性。在多数种群对比分析中，历史与当代钻纹龟的基因流估计值普遍较低（m≈0.01）。但本研究检测到，当代从切萨皮克湾外种群迁入湾内的基因流，以及湾内两个种群间的基因流均出现显著提升，这一现象可能与20世纪早期的人为移殖活动相关。本研究表明，评估种群连通性需结合多时间尺度的推断结果，尤其是近期的种群动态变化可帮助识别威胁种群存续的风险因素。