Of peaks and valleys: testing the roles of orogeny and habitat heterogeneity in driving allopatry in mid-elevation frogs (Aromobatidae: Rheobates) of the northern Andes

Abstract

Aim The frog genus Rheobates (Anura: Aromobatidae) is endemic to mid-elevations in the Colombian Andes. Our aim was to evaluate the role of the northern Andean high peaks and the low Magdalena Valley in creating barriers to dispersal and promoting vicariance within Rheobates. Location Three disjunct mid-elevation flanks of the northern Colombian Andes: the eastern and western flanks of the Eastern Cordillera, separated by high mountain peaks, and the eastern flank of the Central Cordillera, separated from the Eastern Cordillera by the arid Magdalena Valley. Methods We analysed mitochondrial and nuclear DNA sequences from 37 individuals of Rheobates to infer their phylogenetic relationships, divergence times and ancestral areas. We used species distribution models to test the role of climatic variables in determining the present geographical boundaries of the species. Results The phylogeny of Rheobates is largely predicted by geography, with one population from the eastern flank of the Eastern Cordillera sharing a most recent common ancestor with all other Rheobates 21 million years ago (Ma; 95% credible interval 31-10 Ma). Populations in the Central Cordillera were monophyletic, isolated across the Magdalena Valley with a divergence time estimated at 13 Ma (19-7 Ma). We also detected one recent crossing of the Eastern Cordillera, along with unanticipated latitudinal phylogeographical structure within the western flank of the Eastern Cordillera. Environmental niche tests indicated that the Magdalena Valley and the high peaks of the Eastern Cordillera are significant environmental barriers for Rheobates populations. Main conclusions Diversification in Rheobates coincided with the early Miocene uplift of Colombia's Eastern Cordillera and the hypothesized onset of aridity in the Magdalena Valley during the middle Miocene. Our study offers broad support for the classic mountain orogeny model of vicariant divergence, but suggests that lowland habitat heterogeneity also played a long-term role in promoting vicariance, despite a long history of palaeoclimatic fluctuations.