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When are adaptive radiations replicated in areas? Ecological opportunity and unexceptional diversification in West Indian dipsadine snakes (Colubridae: Alsophiini)

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Aim  We examine diversification in Caribbean alsophiine snakes and hypothesize that, given the ecological opportunity presented by colonization of the West Indies, alsophiines should show the signature of an early burst of diversification and associated low within‐clade ecological and morphological disparification. We also test whether changes in morphology and ecology are associated with changes in diversification rate, as trait‐dependent diversification is hypothesized to affect historical inferences of diversification and disparification. Finally, as replicated radiations are found across the West Indies in the anoles, we test for significant differences in ecological and morphological assemblages and rates among the major island groups.

Location  The West Indies.

Methods  A time‐calibrated phylogeny produced from six genes using relaxed clock methods in beast was constructed to estimate ancestral areas using Lagrange. Maximum body size and ecological niche were scored for all species in the phylogeny, and comparative phylogenetic methods in R using geiger, laser, ape and our own code were used to examine diversification through time, disparification and trait‐dependent diversification from this dated phylogeny.

Results  The pattern of species diversification did not differ significantly from the Yule model of diversification. Morphology and ecology fitted a Brownian and white noise model of diversification, respectively. Although not significantly different, morphological disparification was lower than the Brownian null model, whereas ecological disparification was significantly greater than the null. Trait‐dependent diversification analyses suggested that the constant null models provided the best fit to these data. There was no significant signal of rate variation among the major island groups for size, but moderate evidence for niche.

Main conclusions  Although ecological opportunity was similarly present for alsophiines as it was for anoles, the snakes fail to show an early burst of speciation. Potential reasons for this include the young age of the group, and staggered diversification due to waiting times between island colonization. In turn, ecological and morphological disparities do not necessarily follow predictable patterns related to species diversification. Thus, the presence of ecological opportunity alone is not necessarily sufficient to trigger replicated adaptive radiations in areas.
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Document Type: Research Article

Affiliations: Department of Biological Sciences, The George Washington University, 2023 G Street NW, Washington, DC, 20052, USA

Publication date: March 1, 2012

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