Here we use population genomic data (ddRAD-Seq) and ecological niche modeling to test biogeographic hypotheses for the divergence of the island-endemic cactus species Cereus insularis Hemsl. (Cereeae; Cactaceae) from its sister species C. fernambucensis Lem. The Cereus insularis grows in the Fernando de Noronha Islands (FNI), a Neotropical archipelago located 350 km off the Brazilian Atlantic Forest (BAF) coast. Phylogeographic reconstructions support a northward expansion by the common ancestor of C. insularis and C. fernambucensis along the mainland BAF coast, with C. insularis diverging from the widespread mainland taxon C. fernambucensis after colonizing FNI in the late Pleistocene. The morphologically distinct C. insularis is monophyletic and nested within C. fernambucensis, as expected from a progenitor-derivative speciation model. We tested alternative biogeographic and demographic hypotheses for the colonization of the FNI using Approximate Bayesian Computation. We found the greatest support for a stepping-stone path that emerged during periods of decreased sea level (the “bridge” hypothesis), in congruence with historical ecological niche modeling that shows highly suitable habitats on stepping-stone islands during glacial periods. The outlier analyses reveal signatures of selection in C. insularis, suggesting a putative role of adaptation driving rapid anagenic differentiation of this species in FNI.

在这里，我们使用群体基因组数据 (ddRAD-Seq) 和生态位模型来测试岛屿特有仙人掌物种Cereus insularis Hemsl 分歧的生物地理学假设。 （Cereeae；仙人掌科）来自其姐妹种C. fernambucensis Lem。仙人掌生长在费尔南多-迪诺罗尼亚群岛 (FNI)，这是一个新热带群岛，距离巴西大西洋森林 (BAF) 海岸 350 公里。系统发育地理学重建支持C. insularis和C. fernambucensis的共同祖先沿着大陆 BAF 海岸向北扩张， C. insularis在晚更新世殖民 FNI 后与广泛分布的大陆分类群C. fernambucensis分离。形态上不同的C. insularis是单系的，并且嵌套在C. fernambucensis内，正如祖先衍生物种形成模型所预期的那样。我们使用近似贝叶斯计算测试了 FNI 殖民化的替代生物地理和人口假设。我们发现，在海平面下降期间出现的垫脚石路径（“桥梁”假说）得到了最大的支持，这与历史生态位模型一致，该模型显示了冰川时期垫脚石岛上非常适合的栖息地。离群值分析揭示了C. insularis的选择特征，表明适应在 FNI 中驱动该物种快速生长分化的假定作用。