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类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，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。本研究对比了当代种群衰退、当代生态边缘效应与冰期后分布区变迁三类因素的影响。通过采用经典模型比较流程与贝叶斯方法，本研究对北美异交林木灰胡桃（Juglans cinerea L.）的29个种群展开分析，结果证实冰期后分布区变迁是决定其遗传多样性、遗传分化与遗传瓶颈的核心驱动因素。尽管灰胡桃因外来真菌病原体侵染，在20世纪经历了种群规模的大幅衰退，但本研究分析显示：近期的种群衰退对其遗传层面的影响，要弱于冰期后种群重定殖的历史效应。种群所处的分布区边缘与核心位置差异，同样无法解释观测到的多样性与分化格局。本研究结果表明：林木大规模近期种群减少所带来的遗传影响，应当结合更新世时期的大规模分布区变迁加以考量——这类变迁可能已对物种的遗传特征产生了长期效应。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工作、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。