Data from: Divergence maintained by climatic selection despite recurrent gene flow: a case study of Castanopsis carlesii (Fagaceae)

Local adaptation to different environments has the potential to maintain divergence between populations despite recurrent gene flow and is an important driver for generating biological diversity. In this study, we investigate the role of adaptation in the maintenance of two parapatric varieties of a forest tree. We used sequence variation of chloroplastic DNA and restriction site-associated DNA to investigate the genetic structure of two varieties of Castanopsis carlesii in subtropical China and relate it to climatic variation. We used niche reconstruction methods to investigate niche differentiation between the two varieties and to estimate the past distribution of this species. A deep divergence was observed between the two varieties, but evidence of introgression and genetic admixture was detected in two phenotypically and geographically intermediate populations. Niche reconstruction suggests that the distribution of the two varieties was disjunct during periods of global cooling and that the two varieties occupy significantly different niches. The genetic structure was mainly driven by environmental factors, and 13 outlier loci under divergent selection were correlated with climatic variation. These results suggest that the two varieties evolved in allopatry and came back into secondary contact after the last glacial maximum and that they are an evolutionary example of divergence maintained by climatic selection despite recurrent gene flow.

尽管存在经常性的基因流，针对不同环境的局部适应仍可维持种群间的分化，亦是驱动生物多样性产生的关键驱动力。本研究聚焦于适应作用在两种邻域分布的（parapatric）森林树木变种维持中的角色。研究利用叶绿体DNA（chloroplastic DNA）与限制性酶切位点相关DNA（restriction site-associated DNA）的序列变异，对中国亚热带地区两种米锥（Castanopsis carlesii）变种的遗传结构展开分析，并将其与气候变异相关联。此外，本研究采用生态位重建方法，探究两种变种间的生态位分化情况，并推演该物种的历史分布范围。研究观测到两种变种间存在深度分化，但在两个表型与地理上均处于中间过渡状态的种群中，检测到了基因渐渗（introgression）与遗传混合的信号。生态位重建结果显示，在全球变冷时期，两种变种的分布曾呈现间断状态，且二者占据的生态位存在显著差异。种群遗传结构主要受环境因子驱动，且13个受到歧化选择的异常位点（outlier loci）与气候变异显著相关。上述结果表明，两种变种曾在异域分布（allopatry）状态下演化，并在末次冰盛期后再度形成次生接触；它们亦是一个典型的进化案例：尽管存在经常性的基因流，二者仍通过气候介导的歧化选择维持了种群分化。