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Inferring the evolutionary and biogeographic history of taxa occurring in a particular region is one way to determine the processes by which the biodiversity of that region originated. Tree boas of the genus Corallus are an ancient clade and occur throughout Central and South America and the Lesser Antilles, making it an excellent group for investigating Neotropical biogeography. Using sequenced portions of two mitochondrial and three nuclear loci for individuals of all recognized species of Corallus, we infer phylogenetic relationships, present the first molecular analysis of the phylogenetic placement of the enigmatic C. cropanii, develop a time-calibrated phylogeny, and explore the biogeographic history of the genus. We found that Corallus diversified within mainland South America, via over-water dispersals to the Lesser Antilles and Central America, and via the traditionally recognized Panamanian land bridge. Divergence time estimates reject the South American Caribbean-Track as a general biogeographic model for Corallus and implicate a role for events during the Oligocene and Miocene in diversification such as marine incursions and the uplift of the Andes. Our findings also suggest that recognition of the island endemic species, C. grenadensis and C. cookii, is questionable as they are nested within the widely distributed species, C. hortulanus. Our results highlight the importance of using widespread taxa when forming and testing biogeographic hypotheses in complex regions and further illustrate the difficulty of forming broadly applicable hypotheses regarding patterns of diversification in the Neotropical region., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Climatic changes associated with Pleistocene glacial cycles profoundly affected species distributions, patterns of interpopulation gene flow, and demography. In species restricted to montane habitats, ranges may expand and contract along an elevational gradients in response to environmental fluctuations and create high levels of genetic variation among populations on different mountains. The salamander Plethodon fourchensis is restricted to high-elevation, mesic forest on five montane isolates in the Ouachita Mountains. We used DNA sequence data along with ecological niche modelling and coalescent simulations to test several hypotheses related to the effects of Pleistocene climatic fluctuations on species in montane habitats. Our results revealed that P. fourchensis is composed of four well-supported, geographically structured lineages. Geographic breaks between lineages occurred in the vicinity of major valleys and a narrow high-elevation pass. Ecological niche modelling predicted that environmental conditions in valleys separating most mountains are suitable; however, interglacial periods like the present are predicted to be times of range expansion in P. fourchensis. Divergence dating and coalescent simulations indicated that lineage diversification occurred during the Middle Pleistocene via the fragmentation of a wide-ranging ancestor. Bayesian skyline plots showed gradual decreases in population size in three of four lineages over the most recent glacial period and a slight to moderate amount of population growth during the Holocene. Our results not only demonstrate that climatic changes during the Pleistocene had profound effects on species restricted to montane habitats, but comparison of our results for P. fourchensis with its parapatric, sister taxon, P. ouachitae, also emphasizes how responses can vary substantially even among closely related, similarly distributed taxa.

Sky islands provide ideal opportunities for understanding how climatic changes associated with Pleistocene glacial cycles influenced species distributions, genetic diversification, and demography. The salamander Plethodon ouachitae is largely restricted to high-elevation, mesic forest on six major mountains in the Ouachita Mountains. Because these mountains are separated by more xeric, low-elevation valleys, the salamanders appear to be isolated on sky islands where gene flow among populations on different mountains may be restricted. We used DNA sequence data along with ecological niche modelling and coalescent simulations to test several hypotheses related to diversifications in sky island habitats. Our results revealed that P. ouachitae is composed of seven well-supported lineages structured across six major mountains. The species originated during the Late Pliocene, and lineage diversification occurred during the Middle Pleistocene in a stepping stone fashion with a cyclical pattern of dispersal to a new mountain followed by isolation and divergence. Diversification occurred primarily on an east-west axis, which is likely related to the east-west orientation of the Ouachita Mountains and the more favourable cooler and wetter environmental conditions on north slopes compared to south-facing slopes and valleys. All non-genealogical coalescent methods failed to detect significant population expansion in any lineages. Bayesian skyline plots showed relatively stable population sizes over time, but indicated a slight to moderate amount of population growth in all lineages starting approximately 10 000-12 000 years ago. Our results provide new insight into sky island diversifications from a previously unstudied region, and further demonstrate that climatic changes during the Pleistocene had profound effects on lineage diversification and demography, especially in species from environmentally sensitive habitats in montane regions.