Data from: Can physiographic regions substitute for genetically-determined conservation units? A case study with the threatened plant, Silene spaldingii

Protecting genetic diversity throughout the range of a species is important for conservation, as doing so provides for long-term evolutionary potential and persistence under a changing environment. Conservation of diversity at the intraspecific level requires identification of all genetically distinct population segments within species; i.e., conservation units (CUs). Silene spaldingii occurs in grasslands of the Columbia Plateau region of western North America and is listed as threatened under the Federal Endangered Species Act. The recovery plan identified five physiographic regions across the range of the species to use as surrogates for genetic CUs. We collected leaf samples from an average of 26 plants from each of 19 of the largest populations across all five physiographic regions and used variable microsatellite and chloroplast DNA markers to determine how genetic variation is distributed across the range of the species and how well physiographic regions reflect population structure within this species. Results of several multivariate analyses clustered our samples into four genetic groups which did not correspond well with the physiographic regions. We observed little genetic differentiation among populations in the main range of the species which encompasses nearly all of four contiguous physiographic regions. However, three other distinct genetic groups were identified: two in the disjunct northeast corner and one at the southeast edge of the main range. Modification of the CUs to reflect the genetic groups rather than the physiographic regions would result in CUs which better reflect historical patterns of population structure. Moreover, use of the genetic units to inform translocation and genetic rescue efforts could improve our ability to mimic natural patterns of gene flow. Our results suggest that physiographic regions may not always be an accurate reflection of population structure for threatened or endangered species.

在物种的整个分布范围内保护遗传多样性，对于物种保护工作至关重要——此举可为物种在持续变化的环境中提供长期的进化潜力与存续能力。对物种内遗传多样性的保护，需要先鉴定物种内所有遗传分化的种群单元，即保护单元（Conservation Units, CUs）。斯宝德蝇子草（Silene spaldingii）分布于北美西部哥伦比亚高原地区的草原中，被《联邦濒危物种法》列为受威胁物种。该物种的恢复计划将其分布区划分为五个地貌区域，以作为遗传保护单元的替代指标。我们从五个地貌区域内的19个最大种群中各采集了平均26株植株的叶片样本，并利用多态性微卫星（microsatellite）与叶绿体DNA（chloroplast DNA）分子标记，探究该物种的遗传变异在其分布范围内的分布模式，以及地貌区域能否准确反映该物种种群结构。多项多元分析结果显示，我们的样本被聚为四个遗传类群，但这些类群与预设的五个地貌区域并未形成良好的对应关系。在该物种的主要分布区（涵盖四个相连的地貌区域的绝大部分范围）内，种群间几乎无遗传分化。但在主要分布区之外，还鉴定出三个独立的遗传类群：两个位于东北部的间断分布区域，一个位于主要分布区的东南部边缘。若调整保护单元的划分依据，使其匹配遗传类群而非地貌区域，则新的保护单元将更能反映该物种种群结构的历史演化模式。此外，以遗传类群为依据指导种群迁移与遗传拯救工作，可提升我们模拟自然基因流模式的能力。本研究结果表明，对于受威胁或濒危物种而言，地貌区域未必总能准确反映其种群结构。