Data from: Disentangling the genetic effects of refugial isolation and range expansion in a trans-continentally distributed species

In wide-ranging taxa with historically dynamic ranges, past allopatric isolation and range expansion can both influence the current structure of genetic diversity. Considering alternate historical scenarios involving expansion from either a single refugium or from multiple refugia can be useful in differentiating the effects of isolation and expansion. Here, we examined patterns of genetic variability in the trans-continentally distributed painted turtle (Chrysemys picta). We utilized an existing phylogeographic dataset for the mitochondrial control region and generated additional data from nine populations for the mitochondrial control region (n = 302) and for eleven nuclear microsatellite loci (n = 247). We created a present-day ecological niche model (ENM) for C. picta and hindcast this model to three reconstructions of historical climate to define three potential scenarios with one, two, or three refugia. Finally, we employed spatially-explicit coalescent simulations and an approximate Bayesian computation (ABC) framework to test which scenario best fit the observed genetic data. Simulations indicated that phylogeographic and multilocus population-level sampling both could differentiate among refugial scenarios, although inferences made using mitochondrial data were less accurate when a longer coalescence time was assumed. Furthermore, all empirical genetic datasets were most consistent with expansion from a single refugium based on ABC. Our results indicate a stronger role for post-glacial range expansion, rather than isolation in allopatric refugia followed by range expansion, in structuring diversity in this species. To distinguish among complex historical scenarios, we recommend explicitly modeling the effects of range expansion and evaluating alternate refugial scenarios for wide-ranging taxa.对于具有历史动态分布范围的广布分类群而言，过往的异域隔离（allopatric isolation）与分布区扩张均可影响当前的遗传多样性结构。考虑源自单一避难所（refugium）或多个避难所的不同历史情景，有助于区分隔离与扩张所产生的效应。本研究以跨大陆分布的锦龟（*Chrysemys picta*）为研究对象，分析其遗传变异模式。我们利用已有的线粒体控制区（mitochondrial control region）系统地理数据集，并新增了9个种群的线粒体控制区数据（n=302）与11个核微卫星位点（nuclear microsatellite loci）的数据（n=247）。我们构建了锦龟当前的生态位模型（ENM），并将该模型回溯预测至三种历史气候重建场景，以此定义包含1个、2个或3个避难所的三种潜在情景。最后，我们采用空间显式溯祖模拟（coalescent simulations）与近似贝叶斯计算（ABC）框架，检验哪种情景最契合观测到的遗传数据。模拟结果显示，系统地理与多位点种群水平采样均可区分不同的避难所情景，但当假设溯祖时间较长时，基于线粒体数据的推断准确性有所降低。此外，基于近似贝叶斯计算分析，所有实证遗传数据集均最符合单一避难所扩张的情景。本研究结果表明，在该物种种群多样性的构建过程中，冰期后分布扩张的作用要强于异域避难所隔离后再扩张的作用。为区分复杂的历史情景，我们建议显式建模分布扩张的效应，并为广布分类群评估不同的避难所情景。