Data from: Model-based analysis supports interglacial refugia over long-dispersal events in the diversification of two South American cactus species

Pilosocereus machrisii and P. aurisetus are cactus species within the P. aurisetus complex, a group of eight cacti that are restricted to rocky habitats within the Neotropical savannas of eastern South America. Previous studies have suggested that diversification within this complex was driven by distributional fragmentation, isolation leading to allopatric differentiation, and secondary contact among divergent lineages. These events have been associated with Quaternary climatic cycles, leading to the hypothesis that the xerophytic vegetation patches which presently harbor these populations operate as refugia during the current interglacial. However, owing to limitations of the standard phylogeographic approaches used in these studies, this hypothesis was not explicitly tested. Here we use Approximate Bayesian Computation to refine the previous inferences and test the role of different events in the diversification of two species within P. aurisetus group. We used molecular data from chloroplast DNA and simple sequence repeats loci of P. machrisii and P. aurisetus, the two species with broadest distribution in the complex, in order to test if the diversification in each species was driven mostly by vicariance or by long-dispersal events. We found that both species were affected primarily by vicariance, with a refuge model as the most likely scenario for P. aurisetus and a soft vicariance scenario most probable for P. machrisii. These results emphasize the importance of distributional fragmentation in these species, and add support to the hypothesis of long-term isolation in interglacial refugia previously proposed for the P. aurisetus species complex diversification.

毛柱属（Pilosocereus）的Pilosocereus machrisii与Pilosocereus aurisetus隶属于P. aurisetus复合群——这是一个由8种仙人掌组成的类群，仅分布于南美洲东部新热带稀树草原的岩生生境中。既往研究表明，该复合群的物种多样化由分布片段化、隔离引发的异域分化，以及不同分化谱系间的二次接触所驱动，上述事件与第四纪气候周期密切相关，由此提出假说：当前承载这些种群的旱生植被斑块在当前间冰期期间充当了物种避难所。然而，由于此前研究采用的标准系统地理学方法存在局限性，该假说未得到明确检验。本研究利用近似贝叶斯计算（Approximate Bayesian Computation）优化了既往推论，并检验了不同事件在P. aurisetus复合群两个物种多样化过程中的作用。我们获取了该复合群中分布最广的两个物种——P. machrisii与P. aurisetus的叶绿体DNA（chloroplast DNA）以及简单序列重复（simple sequence repeats）位点分子数据，以此检验每个物种的多样化主要由分替事件还是长距离扩散事件驱动。研究结果显示，两个物种均主要受分替事件影响：P. aurisetus最适配避难所模型，而P. machrisii最适配软分替模型。本研究结果凸显了分布片段化在这两个物种演化中的重要性，并为此前提出的"P. aurisetus复合群物种多样化依赖间冰期避难所长期隔离"的假说提供了新的支持证据。