The Complete Mitochondrial Genomes Of Three Pleurodiran Turtles And Molecular Phylogenetic And Dating Analyses Using Mitochondrial DNA In Pleurodira

Pleurodira, living in limited areas of the Southern hemisphere, represent a quarter of the species diversity in Testudinata, Which was one of Earth's most instantly recognizable life forms. The complete mitochondrial genome (mtDNA) of two chelids, Chelodina rugosa and Chelus fimbriata, and a podocnemidid, Podocnemis unifilis were determined using PCR,Long–PCR with length of 16,592 bp, 16,661bp and 16,493 bp, respectively. The genome organization, gene order, and base composition was similar to that of typical vertebrate, including 22 tRNAs, 2 rRNAs, 13 protein–coding genes, and a noncoding region, control region (CR). Comparing to the origin of replication for the light–strand (OL) of most mtDNA of vertebrate (especially including all the published Cryptodira), the nocoding sequence between tRNAAsn and tRNACys gene could not function as OL in the three pleurodiran turtles. Together with the losse of OL in Pelomedusa subrufa, these losse of OL may suggest as a common character in Pleurodira. The structure of CRs was semblable between the three pleurodiran turtles and the published Pelomedusa subrufa. All the CSB domain of pleurodiran turtles CRs lack CSB2 and CSB3, which were located in the CSB domain of all the cryptodiran turtles. Therefore, the lack of CSB2 and CSB3 may be another common character in Pleurodira.The phylogenetic and dating analyses among major pleurodiran turtle lineages were conducted based on concatenated dataset (10,254bp) of 12 protein–coding genes of mtDNA from 31 turtle taxa, and Alligator sinensis and Alligator mississippiensis as outgroups. The phylogenetic trees showed similar topologies, and the results strongly supported that the reciprocal monophyly of Pleurodira and Cryptodira, and the divergence time was in Late Triassic (～203.55 mya, 95% HPD: 202.10– 207.60 mya). Pelomedusidae and Podocnemididae formed a monophyletic Pelomedusidae sensu lato, and diverge in Early Cretaceous(～108mya, 95% HPD: 71.91–142.10 mya), which was consistent with the estimation of of the timing of South American/African separation and the fossil record. Chelodina and Chelus formed a monophyletic Chelidae in our study. The dating analyses showed that Chelodina and Chelus separated in Late Cretaceous(～93 mya, 95% HPD: 55.87–128.32 mya), which accorded with the chelid fossil record and suggested the species diversity in Chelidae from Australia and South America might be promoted by the continental drift of Australia from the remaining Ganwana and the geographical isolation of these continent.