Data from: Range-wide distribution of genetic diversity in the North American tree Juglans cinerea: a product of range shifts, not ecological marginality or recent population decline

The spatial distribution of genetic diversity is a product of recent and historical ecological processes, as well as anthropogenic activities. A current challenge in population and conservation genetics is to disentangle the relative effects of these processes, as a first step in predicting population response to future environmental change. In this investigation we compare the influence of contemporary population decline, contemporary ecological marginality, and postglacial range shifts. Using classical model comparison procedures and Bayesian methods, we have identified postglacial range shift as the clear determinant of genetic diversity, differentiation, and bottlenecks in 29 populations of butternut, Juglans cinerea L., a North American outcrossing forest tree. Although butternut has experienced dramatic 20th century decline due to an introduced fungal pathogen, our analysis indicates that recent population decline has had less genetic impact than postglacial recolonization history. Location within the range edge vs. the range core also failed to account for the observed patterns of diversity and differentiation. Our results suggest that the genetic impact of large-scale recent population losses in forest trees should be considered in the light of Pleistocene-era large-scale range shifts that may have had long-term genetic consequences. The data also suggest that the population dynamics and life history of wind-pollinated forest trees may provide a buffer against steep population declines of short duration, a result having important implications for habitat management efforts, ex-situ conservation sampling, and population viability analysis.

遗传多样性的空间分布格局，是近期与历史生态过程以及人为活动共同作用的产物。种群遗传学与保护遗传学领域当前的核心挑战之一，便是厘清这些过程的相对影响——这亦是预测种群对未来环境变化响应的首要步骤。本研究对比了三类因素的作用：当代种群衰退、当代生态边缘性，以及冰期后的分布范围变迁。本研究采用经典模型比较方法与贝叶斯（Bayesian）方法，对北美异交林木灰胡桃（Juglans cinerea L.）的29个种群开展分析，结果明确证实冰期后分布范围变迁是其遗传多样性、遗传分化与遗传瓶颈的决定性因素。尽管灰胡桃在20世纪因外来真菌病原物的侵染出现了大规模种群衰退，但本研究分析显示，近期的种群衰退对其遗传的影响远不及冰期后再定殖历史。种群所处的分布区边缘还是核心位置，同样无法解释观测到的遗传多样性与分化格局。本研究结果表明，在评估林木大规模近期种群流失的遗传影响时，应结合更新世时期的大规模分布范围变迁进行考量——这类变迁或已对种群产生了长期的遗传效应。本研究数据同时显示，风媒传粉林木的种群动态与生活史特征，或可缓冲短期剧烈的种群衰退；这一结论对栖息地管理、迁地保护（ex-situ conservation）采样以及种群生存力分析（population viability analysis）均具有重要的指导意义。