Gene flow and Andean uplift shape the diversification of Gasteracantha cancriformis (Araneae: Araneidae) in Northern South America

Abstract

AimThe Andean uplift has played a major role shaping the current Neotropical biodiversity. However, in arthropods other than butterflies, little is known about how this geographic barrier has impacted species historical diversification. Here we examined the phylogeography of the widespread and color polymorphic spider Gasteracantha cancriformis to: (i) evaluate the effect of the northern Andean uplift on its divergence and, (ii) assess whether its diversification occurred in the presence of gene flow.\n\nLocationNorthern Andes and Brazil\n\nMethodsWe inferred phylogenetic relationships and divergence times in G. cancriformis using mitochondrial and nuclear data from 105 individuals in northern South America. Genetic diversity, divergence and population structure were quantified. We also compared multiple demographic scenarios for this species using a model-based approach (PHRAPL) to establish divergence with or without gene flow. Finally, we evaluated the association between genetic variation and color polymorphism.\n\nResultsBoth nuclear and mitochondrial data supported two well-differentiated clades, which correspond to populations occurring in opposite sides of the Eastern cordillera of the Colombian Andes. The splitting between these clades occurred in the early Pleistocene, around 2.13 million years ago (95% HPD = 0.98-3.93).\n\nDespite this vicariant event, there is shared genetic variation between the clades, which is better explained by a scenario of historical divergence in the face of gene flow. Color polymorphism was randomly scattered in both clades and is not statistically associated with the genetic variation studied here.\n\nMain ConclusionsThe final uplift of Eastern cordillera of the Colombian Andes was identified as the major force that shaped the diversification of G. cancriformis in Northern South America, resulting in a cis- and trans-Andean phylogeographic structure for the species. The divergence in the face of gene flow between cis- and trans-Andean populations found for this spider has been likely facilitated by the presence of low-elevation passes across the Eastern Colombian cordillera. Our work constitutes the first example where the Andean uplift coupled with gene flow influenced the evolutionary history of an arachnid lineage.