Molecular Phylogeny for Marine Turtles Based on Sequences of the ND4-Leucine tRNA and Control Regions of Mitochondrial DNA

Marine turtles are divided into two families, the Dermochelyidae and the Cheloniidae. The majority of species are currently placed within the two tribes of the Cheloniidae, the Chelonini and the Carettini, but debate continues over generic and tribal affinities as well as species boundaries. We used nucleotide sequences (907 bp) from the ND4–LEU tRNA region and the control region (526 bp) of mitochondrial DNA to resolve areas of uncertainty in marine turtle (Chelonioidae) systematics. The ND4–LEU tRNA fragment was more conserved than the fragment from the control region, with sequence divergences ranging from 0.026 to 0.148 and 0.067 to 0.267, respectively. Parsimony analysis based only on the ND4–LEU tRNA data suggests that the hawksbill,Eretmochelys imbricata,lies within the tribe Carettini and is closely related to the genusCaretta,but could not resolve the position of the flatback,Natator depressus.A similar analysis based only on the control region sequence data suggested thatN. depressusis affiliated with the Chelonini, but failed to resolve the position ofE. imbricataand the loggerhead,Caretta caretta.In contrast to these results, the combination of both data sets with published cytochrome b data produced a phylogeny based on 1924 bp of sequence data which resolves the position ofE. imbricatarelative toCarettaandLepidochelysand joinsN. depressusas sister to the Carettini. Based on the molecular data, the Chelonini contains theCheloniaspecies, while the Carettini contains the remaining species of Cheloniidae. The control region sequence divergence between Pacific and Atlantic populations of the leatherback,Dermochelys coriacea,was relatively low (0.0081) when compared with the green turtle,Chelonia mydas(0.071–0.074). Atlantic and Pacific populations ofCh. mydaswere found to be paraphyletic with respect to the black turtle,Ch. agassizi,suggesting that the current taxonomic designations within the PacificCheloniaare questionable. This analysis shows the utility of combining sequence data for different regions of mtDNA that by themselves are insufficient to obtain robust phylogenies.