Population Genetics of the Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis) across Multiple Spatial Scales

Conservation genetics is a powerful tool to assess the population structure of species and provides a framework for informing management of freshwater ecosystems. As lotic habitats become fragmented, the need to assess gene flow for species of conservation management becomes a priority. The eastern hellbender (Cryptobranchus alleganiensis alleganiensis) is a large, fully aquatic paedamorphic salamander. Many populations are experiencing declines throughout their geographic range, yet the genetic ramifications of these declines are currently unknown. To this end, we examined levels of genetic variation and genetic structure at both range-wide and drainage (hierarchical) scales. We collected 1,203 individuals from 77 rivers throughout nine states from June 2007 to August 2011. Levels of genetic diversity were relatively high among all sampling locations. We detected significant genetic structure across populations (Fst values ranged from 0.001 between rivers within a single watershed to 0.218 between states). We identified two genetically differentiated groups at the range-wide scale: 1) the Ohio River drainage and 2) the Tennessee River drainage. An analysis of molecular variance (AMOVA) based on landscape-scale sampling of basins within the Tennessee River drainage revealed the majority of genetic variation (∼94–98%) occurs within rivers. Eastern hellbenders show a strong pattern of isolation by stream distance (IBSD) at the drainage level. Understanding levels of genetic variation and differentiation at multiple spatial and biological scales will enable natural resource managers to make more informed decisions and plan effective conservation strategies for cryptic, lotic species.

保护遗传学（Conservation genetics）是评估物种种群结构的有力工具，可为淡水生态系统的管理决策提供理论支撑框架。随着流水生境（lotic habitats）日益破碎化，对保护优先物种开展基因流评估的需求愈发紧迫。东部隐鳃鲵（Cryptobranchus alleganiensis alleganiensis）是一种大型、完全水生的幼态持续型蝾螈（paedamorphic salamander）。该物种在其整个分布区内的多数种群均出现衰退，但目前这类衰退所带来的遗传后果尚不明确。为此，我们分别从全域分布尺度与流域层级尺度两个维度，对遗传变异水平与种群遗传结构进行了分析。2007年6月至2011年8月期间，我们从全美9个州的77条河流中共计采集了1203个实验个体。所有采样位点的遗传多样性水平均处于较高水平。我们检测到种群间存在显著的遗传分化结构：固定分化指数（Fst）值范围为0.001（同一流域内的河流间）至0.218（州际间）。在全域分布尺度下，我们鉴定出两个遗传分化显著的类群：1）俄亥俄河流域（Ohio River drainage）；2）田纳西河流域（Tennessee River drainage）。针对田纳西河流域内各盆地开展的景观尺度采样的分子变异分析（Analysis of Molecular Variance, AMOVA）结果显示，绝大多数遗传变异（约94%~98%）存在于河流内部。东部隐鳃鲵在流域尺度上呈现出显著的河流距离隔离（Isolation by Stream Distance, IBSD）模式。明晰多空间尺度与生物学尺度下的遗传变异与分化水平，可帮助自然资源管理者制定更具科学性的决策，并为隐秘性流水物种类群规划高效的保护策略。