RESUMO
The Caribbean rock iguana, Cyclura, has had an unstable intrageneric taxonomy and an unclear phylogenetic position within the family Iguanidae. We use mtDNA sequence data to address these issues and explore the phylogeographic history of the genus. ND4 to leucine tRNA sequence data were collected from multiple individuals of each of the eight species of Cyclura (including 15 of 16 subspecies) and from four localities of Iguana iguana (representative of this species' broad geographic range). This data set was combined with sequence data from Sites et al. (1996, Mol. Biol. Evol. 13, 1087-1105) and analyzed under maximum-parsimony and maximum-likelihood optimization criteria. The ND4 region provided good resolution for the majority of nodes, as indicated by high bootstrap support. In agreement with several recent molecular studies, Cyclura is recovered as monophyletic and is not closely related to any other genus, whereas Iguana is strongly supported as the sister taxon to Sauromalus. This result is statistically more likely than other published hypotheses of Iguanid relationships. Cyclura shows a southeast to northwest speciation sequence in the Caribbean, with the most ancient lineage on the Puerto Rican Bank. The amount of interspecific sequence divergence within Cyclura (maximum 11.4%) is very high in comparison to data from other iguanid taxa at this locus, suggesting that this group either has been in the Caribbean for a very long time or has gone through a very rapid rate of evolution at this locus. Using dates from other published studies, we calculate a molecular clock that suggests that Cyclura colonized the Caribbean between 15 and 35 mya. Several questions regarding subspecific taxonomy are raised in the analysis and await further investigation using a more rapidly evolving marker such as nuclear microsatellites.