Phylogeography and hybridization in Ctenosaura species (Sauria, Iguanidae) from Caribbean Honduras: insights from mitochondrial and nuclear DNA

摘要

In order to infer the phylogenetic relationships and biogeographical patterns in Hondur-an spiny-tailed iguanas (Ctenosaura), we analyzed partial sequences of the mitochondrial NADH dehydrogenase subunit 4 (ND4) gene. In addition, we used nuclear sequences of the internal transcribed spacer 2 of the large ribosomal subunit (ITS2) to test whether hybridization occurs in two Ctenosaura species on the Honduran Utila Island as reported in former morphology-based studies. The phylogenetic trees based on ND4 support the current classification of Ctenosaura and its subdivision into three subgenera. The low average interspecific sequence divergence of 1-2% within the clade Loganiosaura that comprises C. bakeri, C. oedirhina, and C. melanosterna indicates their rather recent evolutionary origin. Another clade of Ctenosaura is represented by C. similis, which occurs on Utila and Guanaja as well as across most of Central America. Low genetic differentiation among the Honduran populations of C. similis suggests recent gene flow between them. Comparison of the phylogeographic patterns with the geological history of Caribbean Honduras implies a mixture of dispersal and vicariance events as the most plausible explanation for the current distribution of Ctenosaura in coastal Honduras. Accordingly, Utila has been successively colonized by two species, C. bakeri and C. similis. The comparison of ND4 and ITS2 based trees revealed that both species hybridize. We suggest that hybridization between these originally allopatric species is the result of recent secondary contact due to successive island colonization. We are concerned that habitat destruction leads to increased contacts between the two species, and therefore may increase the rates of introgression. This phenomenon may potentially pose a serious conservation problem for C. bakeri.