Data from: Tests of species-specific models reveal the importance of drought in postglacial range shifts of a Mediterranean-climate tree: insights from integrative distributional, demographic and coalescent modelling and ABC model selection

Past climate change has caused shifts in species distributions and undoubtedly impacted patterns of genetic variation, but the biological processes mediating responses to climate change, and their genetic signatures, are often poorly understood. We test six species-specific biologically informed hypotheses about such processes in canyon live oak (Quercus chrysolepis) from the California Floristic Province. These hypotheses encompass the potential roles of climatic niche, niche multidimensionality, physiological trade-offs in functional traits, and local-scale factors (microsites and local adaptation within ecoregions) in structuring genetic variation. Specifically, we use ecological niche models (ENMs) to construct temporally dynamic landscapes where the processes invoked by each hypothesis are reflected by differences in local habitat suitabilities. These landscapes are used to simulate expected patterns of genetic variation under each model and evaluate the fit of empirical data from 13 microsatellite loci genotyped in 226 individuals from across the species range. Using approximate Bayesian computation (ABC), we obtain very strong support for two statistically indistinguishable models: a trade-off model in which growth rate and drought tolerance drive habitat suitability and genetic structure, and a model based on the climatic niche estimated from a generic ENM, in which the variables found to make the most important contribution to the ENM have strong conceptual links to drought stress. The two most probable models for explaining the patterns of genetic variation thus share a common component, highlighting the potential importance of seasonal drought in driving historical range shifts in a temperate tree from a Mediterranean climate where summer drought is common.

过往的气候变化已引发物种分布范围变迁，且毋庸置疑地对遗传变异模式造成了影响，但介导物种响应气候变化的生物学过程及其遗传特征（genetic signatures），目前仍鲜为学界所深入了解。本研究针对来自加利福尼亚植物区系省（California Floristic Province）的峡谷活栎（Quercus chrysolepis），就上述过程提出6项具备物种特异性与生物学依据的假说并开展检验。这些假说涵盖了气候生态位（climatic niche）、生态位多维性（niche multidimensionality）、功能性状的生理权衡（physiological trade-offs）以及局域尺度因子（微生境与生态区内的局部适应）在塑造遗传变异模式中的潜在作用。具体而言，本研究借助生态位模型（ecological niche models, ENMs）构建时序动态景观，其中各假说所涉及的生物学过程可通过局域生境适宜性的差异得以体现。利用此类景观，本研究可模拟各模型下的预期遗传变异模式，并基于覆盖该物种分布全范围的226个个体的13个微卫星位点（microsatellite loci）基因型数据，评估各模型与实证数据的拟合优度。通过近似贝叶斯计算（approximate Bayesian computation, ABC）方法，本研究获得了两个统计学上无法区分的模型的极强支持证据：其一为权衡模型，该模型提出生长速率与耐旱性共同驱动生境适宜性与遗传结构；其二为基于通用生态位模型估算的气候生态位构建的模型，其中对生态位模型贡献度最高的变量与干旱胁迫（drought stress）存在极强的概念关联性。综上，这两个最能解释遗传变异模式的最优模型共享核心组分，凸显了季节性干旱在驱动夏季干旱频发的地中海气候区温带树木历史分布范围变迁中的潜在重要性。