Understanding why species richness peaks along the Andes is a fundamental question in the study of Neotropical biodiversity. Several biogeographic and diversification scenarios have been proposed in the literature, but there is confusion about the processes underlying each scenario, and assessing their relative contribution is not straightforward. Here, we propose to refine these scenarios into a framework which evaluates four evolutionary mechanisms: higher speciation rate in the Andes, lower extinction rates in the Andes, older colonization times and higher colonization rates of the Andes from adjacent areas. We apply this framework to a species-rich subtribe of Neotropical butterflies whose diversity peaks in the Andes, the Godyridina (Nymphalidae: Ithomiini). We generated a time-calibrated phylogeny of the Godyridina and fitted time-dependent diversification models. Using trait-dependent diversification models and ancestral state reconstruction methods we then compared different biogeographic scenarios. We found strong evidence that the rates of colonization into the Andes were higher than the other way round. Those colonizations and the subsequent local diversification at equal rates in the Andes and in non-Andean regions mechanically increased the species richness of Andean regions compared to that of non-Andean regions (‘species-attractor’ hypothesis). We also found support for increasing speciation rates associated with Andean lineages. Our work highlights the importance of the Andean slopes in repeatedly attracting non-Andean lineages, most likely as a result of the diversity of habitats and/or host plants. Applying this analytical framework to other clades will bring important insights into the evolutionary mechanisms underlying the most species-rich biodiversity hotspot on the planet.
Bibliographical noteFunding Information:
This project was funded by an ATIP (CNRS, France) grant awarded to ME. NC was funded by a doctoral fellowship from Ecole Doctorale 227 (France). ME acknowledges additional funding by the ANR grant SPECREP. CJ and MJ acknowledge funding from the Royal Society (UK). We thank authorities of Peru, Ecuador and Brazil for delivering research and collection permits, as well as many assistants for their help in the field. We are grateful to Haydon Warren-Gash for providing specimens. Molecular work was performed at the GenePool (University of Edinburgh, UK), Unicamp (Brazil) and the Service de Syst?matique Mol?culaire UMS2700 of the MNHN (France). We thank Luiza Magaldi for helping with sequencing of some Brazilian samples. AVLF acknowledges support from the FAPESP (BIOTA-FAPESP 2011/50225-3); from the Brazilian Research Council-CNPq (fellowship 302585/2011-7, and SISBIOTA-Brasil/CNPq grant 563332/2010-7); from two collaborative grants of ?Dimensions US-Biota-S?o Paulo?, US NSF, NASA and FAPESP (grants 2012/50260-6 and 2013/50297-0); and from the National Science Foundation (NSF) (DEB-1256742). KRW also acknowledges support from the Florida Natural History Museum Associates, the National Geographic Society, NSF (DEB-0639861), the Leverhulme Trust and the Darwin Initiative.
- trait-dependent diversification