U.S. Geological Survey, Western Ecological Research Center, San Diego Field Station, San Diego, California, United States of America.
U.S. Geological Survey, Western Ecological Research Center, Santa Cruz Field Station, Santa Cruz, California, United States of America.
PLoS One. 2020 May 5;15(5):e0231744. doi: 10.1371/journal.pone.0231744. eCollection 2020.
Conversion and fragmentation of wildlife habitat often leads to smaller and isolated populations and can reduce a species' ability to disperse across the landscape. As a consequence, genetic drift can quickly lower genetic variation and increase vulnerability to extirpation. For species of conservation concern, quantification of population size and connectivity can clarify the influence of genetic drift in local populations and provides important information for conservation management and recovery strategies. Here, we used genome-wide single nucleotide polymorphism (SNP) data and capture-mark-recapture methods to evaluate the genetic diversity and demography within seven focal sites of the endangered San Francisco gartersnake (Thamnophis sirtalis tetrataenia), a species affected by alteration and isolation of wetland habitats throughout its distribution. The primary goals were to determine the population structure and degree of genetic isolation among T. s. tetrataenia populations and estimate effective size and population abundance within sites to better understand the present and future importance of genetic drift. We also used temporally sampled datasets to examine the magnitude of genetic change over time. We found moderate population genetic structure throughout the San Francisco Peninsula that partitions sites into northern and southern regional clusters. Point estimates of both effective size and population abundance were generally small (≤ 100) for a majority of the sites, and estimates were particularly low in the northern populations. Genetic analyses of temporal datasets indicated an increase in genetic differentiation, especially for the most geographically isolated sites, and decreased genetic diversity over time in at least one site (Pacifica). Our results suggest that drift-mediated processes as a function of small population size and reduced connectivity from neighboring populations may decrease diversity and increase differentiation. Improving genetic diversity and connectivity among T. s. tetrataenia populations could promote persistence of this endangered snake.
野生动物栖息地的转换和破碎化常常导致种群规模缩小和隔离，并降低物种在景观中扩散的能力。因此，遗传漂变会迅速降低遗传多样性，增加物种灭绝的脆弱性。对于受到保护关注的物种，种群规模和连通性的量化可以阐明遗传漂变对当地种群的影响，并为保护管理和恢复策略提供重要信息。在这里，我们使用全基因组单核苷酸多态性（SNP）数据和捕获-标记-重捕方法，评估了濒危的旧金山束带蛇（Thamnophis sirtalis tetrataenia）七个焦点地点的遗传多样性和种群动态，该物种受到其分布范围内湿地栖息地改变和隔离的影响。主要目标是确定 T. s. tetrataenia 种群之间的种群结构和遗传隔离程度，并估计各地点的有效种群大小和种群丰度，以更好地了解遗传漂变的当前和未来重要性。我们还使用随时间采样的数据集来研究遗传变化随时间的幅度。我们发现旧金山半岛各地都存在中度的种群遗传结构，将各地点分为北部和南部区域集群。大多数地点的有效种群大小和种群丰度的点估计值通常较小（≤100），北部种群的估计值尤其低。对时间数据集的遗传分析表明，遗传分化程度增加，特别是对于地理位置最孤立的地点，并且至少在一个地点（Pacifica）的遗传多样性随时间减少。我们的研究结果表明，作为小种群大小和与邻近种群连通性降低的功能的漂变介导过程可能会降低多样性并增加分化。提高 T. s. tetrataenia 种群的遗传多样性和连通性可以促进这种濒危蛇的生存。
