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.

仙人柱属（Pilosocereus）的Pilosocereus machrisii与Pilosocereus aurisetus隶属于P. aurisetus复合群——一类仅分布于南美洲东部新热带稀树草原岩生生境的8种仙人掌类群。既往研究表明，该复合群内的物种分化受分布区碎片化、隔离引发的异域分化，以及分化谱系间的二次接触所驱动。上述事件与第四纪气候旋回密切相关，由此提出假说：当前承载这些类群的旱生植被斑块，在当前间冰期内充当了避难所的角色。然而，由于此类研究中采用的标准系统地理学方法存在局限性，该假说并未得到明确检验。本研究采用近似贝叶斯计算（Approximate Bayesian Computation）对既往推论进行优化，并检验P. aurisetus复合群内两个物种的分化过程中不同事件的作用。我们利用该复合群中分布范围最广的两个物种——P. machrisii与P. aurisetus的叶绿体DNA（chloroplast DNA）与简单序列重复位点（simple sequence repeats）分子数据，以检验各物种种群分化主要由隔离分化还是长距离扩散事件驱动。研究结果显示，两个物种均主要受隔离分化影响：P. aurisetus的最适演化情景为避难所模型，而P. machrisii的最适情景为软隔离分化。上述结果凸显了分布区碎片化在这两个物种演化中的重要性，并为此前提出的“P. aurisetus复合群物种分化源于间冰期避难所中长期隔离”的假说提供了进一步支持。