Background



A major focus of biogeography is understanding the causal factors that explain the spatial patterns of biodiversity and the current distribution of species. The primary formation of species is a key component of the origin of local and regional biodiversity. The division of an ancestral species by vicariance is one of the simplest and widely applicable models for speciation, whether by mountain uplift or by climate fluctuations.



Objectives



Using frogs and other tetrapods, we will look at two case studies of the factors driving species diversity in and around the Eastern Cordillera (EC) of Colombia. First we will use comparative phylogeographic data to evaluate the impact of the uplift of the EC on the isolation and divergence of lowland taxa. Second, we will infer the biogeographic origins of montane frogs in the EC and investigate the spatial patterns of diversification.



Methods



We evaluated the role of the EC in lowland divergence using mitochondrial DNA (mtDNA) sequence data from 37 lineages of tetrapods and analyzed the data using population genetic and phylogenetic tools to evaluate relative and absolute divergence times. To evaluate the role of orogeny in the origin and diversification of montane frogs, we amassed the largest molecular phylogeny of frogs of the genus Pristimantis (Anura: Craugastoridae) to date and applied standard phylogenetic and biogeographic analyses to estimate the spatial and temporal components of species diversification within the EC.



Results



Coalescent analyses revealed general asynchrony in divergence times and recent divergences overall among lowland taxa, plus extensive non-monophyly of mtDNA sequences with respect to the EC. Biogeographic reconstruction of Pristimantis history revealed a mixture of a few independent colonizations of the EC and at least one example of an in situ radiation within high-elevation frogs of the EC. Divergence times among montane frogs tend to predate the Pleistocence.



Implications



Clearly the Andes are a hotspot of species diversity, yet the mechanisms driving or preserving this diversity are well understood only for a handful of lineages. Montane uplift is still cited as a driver of lowland vicariances, yet our integrative re-analyses of diverse datasets revealed very little support for this model, at least among recent divergences. Pliestocene climate fluctuation is often cited as a driver of montane diversification, yet frog species seem much too old. Denser spatial and phylogenetic sampling of amphibians are needed to further test these findings.