State Key Laboratory of Grassland Agro-Ecosystem, School of Life Science, Lanzhou University, Lanzhou, 730000, Gansu, China; Plant Genetics Group, Department of Biology, University of Oulu, 90014, Oulu, Finland.
Mol Ecol. 2014 Jul;23(14):3504-22. doi: 10.1111/mec.12830.
Climate is one of the most important drivers for adaptive evolution in forest trees. Climatic selection contributes greatly to local adaptation and intraspecific differentiation, but this kind of selection could also have promoted interspecific divergence through ecological speciation. To test this hypothesis, we examined intra- and interspecific genetic variation at 25 climate-related candidate genes and 12 reference loci in two closely related pine species, Pinus massoniana Lamb. and Pinus hwangshanensis Hisa, using population genetic and landscape genetic approaches. These two species occur in Southeast China but have contrasting ecological preferences in terms of several environmental variables, notably altitude, although hybrids form where their distributions overlap. One or more robust tests detected signals of recent and/or ancient selection at two-thirds (17) of the 25 candidate genes, at varying evolutionary timescales, but only three of the 12 reference loci. The signals of recent selection were species specific, but signals of ancient selection were mostly shared by the two species likely because of the shared evolutionary history. FST outlier analysis identified six SNPs in five climate-related candidate genes under divergent selection between the two species. In addition, a total of 24 candidate SNPs representing nine candidate genes showed significant correlation with altitudinal divergence in the two species based on the covariance matrix of population history derived from reference SNPs. Genetic differentiation between these two species was higher at the candidate genes than at the reference loci. Moreover, analysis using the isolation-with-migration model indicated that gene flow between the species has been more restricted for climate-related candidate genes than the reference loci, in both directions. Taken together, our results suggest that species-specific and divergent climatic selection at the candidate genes might have counteracted interspecific gene flow and played a key role in the ecological divergence of these two closely related pine species.
气候是影响森林树木适应性进化的最重要因素之一。气候选择对地方适应和种内分化有很大贡献，但这种选择也可能通过生态物种形成促进种间分化。为了检验这一假设，我们使用种群遗传和景观遗传方法，在两个密切相关的松树物种马尾松（Pinus massoniana Lamb.）和黄山松（Pinus hwangshanensis Hisa）中，检查了 25 个与气候相关的候选基因和 12 个参考基因座的种内和种间遗传变异。这两个物种在中国东南部都有分布，但在几个环境变量方面（特别是海拔高度）有相反的生态偏好，尽管在它们的分布重叠的地方形成了杂种。在 25 个候选基因中的三分之二（17 个），在不同的进化时间尺度上，一个或多个稳健的测试检测到了近期和/或古代选择的信号，但只有 12 个参考基因座中的 3 个。近期选择的信号是物种特异性的，但古代选择的信号主要由两个物种共享，可能是因为它们具有共同的进化历史。FST 异常值分析在两个物种之间的五个与气候相关的候选基因中鉴定出了六个受分歧选择的 SNP。此外，基于从参考 SNP 得出的种群历史协方差矩阵，有 24 个候选 SNP 代表九个候选基因，在两个物种的海拔差异中表现出显著相关性。这两个物种之间的遗传分化在候选基因中比在参考基因座中更高。此外，使用隔离与迁移模型的分析表明，候选基因之间的物种间基因流比参考基因座更受限制，无论是在哪个方向。综上所述，我们的结果表明，候选基因中的种特异性和分歧性气候选择可能抵消了种间基因流，并在这两个密切相关的松树物种的生态分化中发挥了关键作用。
