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.

尽管存在反复的基因流（gene flow），针对不同环境的局部适应仍可维持种群间的分化，同时也是驱动生物多样性形成的重要因素。本研究聚焦于一种林木的两个邻域（parapatric）变种，旨在探究适应作用在维持二者分化过程中的功能。本研究利用叶绿体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个米槠（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（niche reconstruction）方法，探究这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。研究发现，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（introgression）与遗传混合（genetic admixture）的证据。生态位重建结果显示，在全球变冷时期，两个变种的分布曾处于间断状态，且二者占据的生态位存在显著差异。该物种的遗传结构主要受环境因素驱动，且13个处于歧化选择（divergent selection）下的异常位点（outlier loci）与气候变异显著相关。上述结果表明，这两个变种曾在异域环境中演化，并在末次冰盛期（last glacial maximum）后再度形成次生接触；它们也成为了一则经典进化案例：即便存在反复的基因流，气候选择仍能维持种群间的分化。