Data from: Footprints of divergent selection in natural populations of Castanopsis fargesii (Fagaceae)

Given predicted rapid climate change, an understanding of how environmental factors affect genetic diversity in natural populations is important. Future selection pressures are inherently unpredictable, so forest management policies should maintain both overall diversity and identify genetic markers associated with the environmental factors expected to change most rapidly, like temperature and rainfall. In this study, we genotyped 648 individuals in 28 populations of Castanopsis fargesii (Fagaceae) using 32 expressed sequence tag (EST)-derived microsatellite markers. After removing six loci that departed from Hardy–Weinberg equilibrium, we measured genetic variation, population structure and identified candidate loci putatively under selection by temperature and precipitation. We found that C. fargesii populations possessed high genetic diversity and moderate differentiation among them, indicating predominant outcrossing and few restrictions to gene flow. These patterns reduce the possible impact of stochastic effects or the influence of genetic isolation. Clear footprints of divergent selection at four loci were discovered. Frequencies of five alleles at these loci were strongly correlated with environmental factors, particularly extremes in precipitation. These alleles varied from being near fixation at one end of the gradient to being completely absent at the other. Our study species is an important forest tree in the subtropical regions of China and could have a major role in future management and reforestation plans. Our results demonstrate that the gene flow is widespread and abundant in natural populations, maintaining high diversity, while diversifying selection is acting on specific genomic regions.

鉴于预估的快速气候变化，解析环境因子如何影响自然种群的遗传多样性具有重要意义。未来的选择压力本质上难以预测，因此森林管理政策既要维持种群整体遗传多样性，也应识别与预计将快速变化的环境因子（如气温与降水）相关的遗传标记。本研究采用32个表达序列标签（expressed sequence tag, EST）来源的微卫星标记（microsatellite markers），对28个种群共648个Castanopsis fargesii（壳斗科Fagaceae）个体进行了基因分型。在剔除6个偏离哈迪-温伯格平衡（Hardy–Weinberg equilibrium）的位点后，我们对其遗传变异、种群结构进行了分析，并鉴定出可能受气温与降水选择的候选位点。研究发现，Castanopsis fargesii种群具有较高的遗传多样性，种群间分化程度中等，这表明其主要以异交为主，基因流受到的限制较少。该特征降低了随机效应或遗传隔离带来的潜在影响。我们在4个位点上发现了明显的歧化选择痕迹。这些位点上的5个等位基因频率与环境因子显著相关，尤其与降水极值的关联度最高。这些等位基因的频率沿环境梯度呈现梯度变化：在梯度一端接近固定，而在另一端则完全缺失。本研究的目标物种是中国亚热带地区的重要森林树种，在未来森林管理与造林计划中可发挥关键作用。研究结果表明，自然种群中基因流广泛且充足，维持了较高的遗传多样性，而歧化选择正作用于特定的基因组区域。