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 to 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.

针对不同环境的局部适应，即便存在持续的基因流，仍可维持种群间的遗传分化，同时也是驱动生物多样性形成的关键因素。本研究旨在探讨适应性作用在维持某林木两个邻域变种分化中的功能。本研究以中国亚热带地区的米槠（Castanopsis carlesii）两个变种为研究对象，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，解析其遗传结构，并将其与气候变异相关联。本研究还采用生态位重建方法，分析两个变种间的生态位分化情况，并推测该物种的历史分布范围。研究观察到两个变种间存在显著的遗传分化，但在两个表型与地理均处于中间状态的种群中检测到了基因渐渗与遗传混合的证据。生态位重建结果显示，在全球冷期阶段，两个变种的分布曾呈间断状态，且二者占据的生态位存在显著差异。其遗传结构主要受环境因子驱动，且13个处于分歧选择下的异常位点与气候变异显著相关。上述结果表明，两个变种曾在异域环境中演化，并在末次冰盛期后发生了二次接触；它们亦是一个典型的进化案例：即便存在持续的基因流，气候选择仍可维持种群间的遗传分化。