ELUCIDATION OF CRYPTIC DIVERSITY IN A WIDESPREAD NEARCTIC TREEFROG REVEALS EPISODES OF MITOCHONDRIAL GENE CAPTURE AS FROGS DIVERSIFIED ACROSS A DYNAMIC LANDSCAPE

Abstract

We investigate the evolutionary history of the wide-ranging Nearctic treefrog Hyla arenicolor through the integration of extensive range-wide sampling, phylogenetic analyses of multilocus genetic data, and divergence dating. Previous phylogeographic studies of this frog documented a potential signature of introgressive hybridization from an ecologically and morphologically divergent sister species. Based on our Bayesian phylogenetic analyses of mitochondrial DNA, we inferred strong phylogeographic structure in H. arenicolor as indicated by seven well-supported clades, five of which correspond to well-defined biogeographic regions. Clades from the Balsas Basin and southwestern Central Mexican Plateau in Mexico, and the Grand Canyon of Arizona, group with the morphologically, behaviorally, and ecologically divergent mountain treefrogs in the H. eximia group, rendering H. arenicolor as paraphyletic. The phylogenetic position of at least two of these three H. arenicolor clades within the H. eximia group, however, is most likely the result of several episodes of introgressive hybridization and subsequent mitochondrial gene capture separated in time and space, as supported by evidence from the nuclear genes. Hyla arenicolor from the Balsas Basin appear to be deeply divergent from other H. arenicolor and represent a distinctly different species. Results suggests that introgressive hybridization events, both ancient and contemporary, coupled with late Neogene vicariance and Pleistocene climate-driven range shifts, have all played a role in the historical diversification of H. arenicolor.