Comparative phylogeography of three widespread species of Anolis across the Puerto Rico Bank Open Access
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Anolis is a species-rich clade, with more than 410 species currently recognized. 173 species of Anolis inhabit the Caribbean, a region with a geological history shaped by volcanism, tectonic movements, and glaciation and interglaciation events. The Puerto Rico Bank, located in the northeast corner of the Caribbean, is a platform that includes Puerto Rico and the Virgin Islands and was exposed as one continuous island several times, from the late Miocene to the Pleistocene. Three species of anoles are found on all of the islands and most of the cays of the Puerto Rico Bank: Anolis cristatellus, A. pulchellus, and A. stratulus. The purpose of this dissertation is to infer phylogeographic patterns for each one of these widespread species, and to interpret them in the context of geological events that could have helped generate the observed patterns. To investigate these relationships, I examine the population genetic structure of each species along the Puerto Rico Bank, and I use coalescent species delimitation methods, which allow the identification of recent speciation events, even when there is no reciprocal monophyly of individual genes. If the present geographic distributions of these species are the result of vicariance caused by island fragmentation since the Last Glacial Maximum, then the phylogenetic patterns should reflect the fragmentation of the islands and the divergence times should be less than 20,000 years. In A. pulchellus, two populations were found and supported as species by a species delimitation analysis: southern Puerto Rico (part of a larger group that extends farther west and north in central Puerto Rico), and eastern Puerto Rico + Virgin Islands. Time of divergence of these populations (3.7 ma) coincides with the northward tilting of the platform, lowland inundations and mountain uplifting. Isolation and reconnection of islands occurred several times during the Quaternary, limiting the genetic divergence between the populations on different (current) islands within the eastern clade. In A. stratulus, five populations were found, but two clades were well-supported in the species tree analysis and in the species delimitation analysis: 1) Puerto Rico + Culebra + Vieques, and 2) Virgin Islands. Divergence between these clades was estimated to have occurred near the Plio-Pleistocene transition (2.6 ma), during the last stages of the inundation of the Virgin Passage. Linear measurements of A. stratulus show that lizards from Puerto Rico, Culebra and Vieques tend to have wider heads and ears and longer limbs than do those from the Virgin Islands. In A. cristatellus, four populations were found, but only two main clades were supported by the species tree and the species delimitation analyses: one for southern Puerto Rico and one for eastern Puerto Rico + Virgin Islands. Anolis cristatellus is paraphyletic, with A. desechensis sister to the southern Puerto Rico population and A. ernestwilliamsi nested within one of the Virgin Islands populations. Time of divergence between the main clades of A. cristatellus was estimated to be 6.4 ma (Late Miocene); however, more extensive sampling of A. cristatellus, including samples from north, west and central Puerto Rico, could change the credible interval of the early diversification event. Gene flow and significant admixture were found at localities in eastern Puerto Rico and the Virgin Islands, supporting the hypothesized contact zone between the subspecies A. c. cristatellus and A. c. wileyae. Molecular differences between A. c. wileyae and A. ernestwilliamsi do not support the latter as a species, and morphological differences previously reported in body size, number of lamellae and size dimorphism, could be the result of gigantism in the Carrot Rock population, explained by the island syndrome.