The Complete Mitochondrial Genome Of Mauremys Mutica And Sacalia Quadriocellata With Implication For Phylogenetic Relationships Among Turtles

In vertebrate animals, mitochondrial DNA (mtDNA) is generally a 15~22 kb circular genome containing 37 genes: 13 protein-coding genes, two rRNA genes, and 22 tRNA genes, as well as a control region. In recent years, mtDNA has been widely used as a useful marker system in numerous phylogenetic analyses of vertebrate relationships because of its maternal mode of inheritance and relative lack of recombination.Turtles have highly specialized morphological characteristics. To date, complete mtDNA genomes have been determined for only 20 species, including 19 cryptodiran turtles and a side-necked turtle.The current taxonomic status of the Clemmys complex of freshwater turtles places the Old World genera Mauremys and Sacalia in the Geoemydidae and the New World genus Clemmys in the Emydinae. These three genera were previously considered to be congeneric, but it was not supported by morphology and chromosome. To address this issue, we sequenced the complete mitochondrial DNA (mtDNA) for the Asian yellow pond turtle (Mauremys mutica) and four eyed-spotted turtle (Sacalia quadriocellata). DNA sequencing was based on the PCR fragments from primer pairs that were designed on the basis of mtDNA sequences of the related turtle species. The genome is 16 609 bp and 16 816 bp, respectively, containing 37 genes (two ribosomal RNA, 22 transfer RNA and 13 protein-coding genes) and a putative control region, a situation that is similar to that found in other vertebrates. The gene organization of the mtDNA studied is typical for vertebrates such as placental mammals, other turtles and skinks, but distinct from that of alligators and snakes.We chose rapidly evolving ND4, the protein-coding gene, which was valuable in lower level questions. We examined the phylogenetic relationships of the Clemmys complex of the freshwater turtles using 985bp of the DNA encoding ND4, a mitochondrial gene and its adjacent tRNA genes. Our results indicated that Mauremys and Sacalia appeared to be sister taxa in the Bataguridae, and suggested the monophyly for the Bataguridae and the Emydidae based on the maximum parsimony (MP) phylogenetic trees. Our studies also suggested that the Bataguridae is not the sister-group with the Emydidae.Furthermore, we conducted maximum parsimony analysis and maximum likelihood using nucleotide sequences of 12 Heavy-strand proteins from twelve turtles, two birds, two crocodilians, two lepidosaurias and one mammal. Analysis of 10 799 aligned nucleotide positions (6 327 informative) led us to hypothesize that turtles are closely related to archosaurs (birds and crocodilians), supporting Tree (((birds, crocodilians), turtles), squamates). This is a significant molecular phylogeny on the placement of turtles relative to the archosaus and lepidosaus. It is likely that turtles originated from a Permian-Triassic archosauromorph ancestor with two pairs of temporal fenestrae behind the skull orbit that were subsequently diminished. Phylogenetic analyses also indicated that group of Trionychoidae was in their more traditional location as the sister taxon to all other hidden-necked turtles, collectively forming the Cryptodira.