| Abstract | We determined the complete nucleotide sequence of the mitochondrial (mt) genome of five individual caecilians (Amphibia: Gymnophiona) representing five of the six recognized families: Rhinatrema bivittatum (Rhinatrematidae), Ichthyophis glutinosus (Ichthyophiidae), Uraeotyphlus cf. oxyurus (Uraeotyphlidae), Scolecomorphus vittatus (Scolecomorphidae), and Gegeneophis ramaswamii (Caeciliidae). The organization and size of these newly determined mitogenomes are similar to those previously reported for the caecilian Typhlonectes natans (Typhlonectidae), and for other vertebrates. Nucleotide sequences of the nuclear RAG1 gene were also determined for these six species of caecilians, and the salamander Mertensiella luschani atifi. RAG1 (both at the amino acid and nucleotide level) shows slower rates of evolution than almost all mt protein-coding genes (at the amino acid level). The new mt and nuclear sequences were compared with data for other amphibians and subjected to separate and combined phylogenetic analyses (Maximum Parsimony, Minimum Evolution, Maximum Likelihood, and Bayesian Inference). All analyses strongly support the monophyly of the three amphibian Orders. The Batrachia hypothesis (Gymnophiona, (Anura, Caudata) receives moderate or good support depending on the method of analysis. Within Gymnophiona, the optimal tree (Rhinatrema, (Ichthyophis, Uraeotyphlus), (Scolecomorphus, (Gegeneophis Typhlonectes) agrees with the most recent morphological and molecular studies. The sister group relationship between Rhinatrematidae and all other caecilians, that between Ichthyophiidae and Uraeotyphlidae, and the monophyly of the higher caecilians Scolecomorphidae+Caeciliidae+Typhlonectidae, are strongly supported, whereas the relationships among the higher caecilians are less unambiguously resolved. Analysis of RAG1 is affected by a spurious local rooting problem and associated low support that is ameliorated when outgroups are excluded. Comparisons of trees using the non-parametric Templeton, Kishino-Hasegawa, Approximately Unbiased, and Shimodaira-Hasegawa tests suggest that the latter may be too conservative.
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