Data from: Tests of species-specific models reveal the importance of drought in postglacial range shifts of a Mediterranean-climate tree: insights from iDDC 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 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.

古气候变化曾引发物种分布范围的变迁，且无疑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印记，目前仍往往缺乏充分的认知。我们针对来自加州植物区省（California Floristic Province）的峡谷活栎（*Quercus chrysolepis*），检验了6项基于物种特异性生物学认知的相关假说，以解析这类生物学过程。这些假说涵盖了气候生态位、生态位多维性、功能性状间的生理权衡，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，我们借助生态位模型（Ecological Niche Models, ENMs）构建了随时间动态变化的景观，在这些景观中，各假说所提出的生物学过程可通过局域生境适宜性的差异得以体现。我们利用这些景观模拟各模型下预期的遗传变异模式，并基于覆盖该物种全分布范围的226个个体的13个微卫星位点（microsatellite loci）基因型数据，评估实证数据与各模型的拟合优度。借助近似贝叶斯计算（Approximate Bayesian Computation, ABC），我们获得了极强的统计支持，证实存在两个统计学上无法区分的最优模型：其一为权衡模型，该模型认为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模型，其中对生态位模型贡献度最高的变量，与干旱胁迫存在极强的概念性关联。因此，用于解释遗传变异模式的两个最优模型共享一个共同核心机制，这凸显了季节性干旱在驱动该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——该区域夏季干旱频发。