Mitochondrial genomes of Japanese Babina frogs (Ranidae, Anura): unique gene arrangements and the phylogenetic position of genus Babina.

Genus Babina is a member of Ranidae, a large family of frogs, currently comprising 10 species. Three of them are listed as endangered species. To identify mitochondrial (mt) genes suitable for future population genetic analyses for endangered species, we determined the complete nucleotide sequences of the mt genomes of 3 endangered Japanese Babina frogs, B. holsti, B. okinavana, and B. subaspera and 1 ranid frog Lithobates catesbeianus. The genes of NADH dehydrogenase subunit 5 (nad5) and the control region (CR) were found to have high sequence divergences and to be usable for population genetics studies. At present, no consensus on the phylogenetic position of genus Babina has been reached. To resolve this problem, we performed molecular phylogenetic analyses with the largest dataset used to date (11,345 bp from 2 ribosomal RNA- and 13 protein-encoding genes) in studies dealing with Babina phylogeny. These analyses revealed monophyly of Babina and Odorrana. It is well known that mt gene rearrangements of animals can provide usable phylogenetic information. Thus, we also compared the mt gene arrangements among Babina species and other related genera. Of the surveyed species, only L. catesbeianus manifested typical neobatrachian-type mt gene organization. In the B. okinavana, an additional pseudogene of tRNA-His (trnH) was observed in the CR downstream region. Furthermore, in the B. holsti and B. subaspera, the trnH/nad5 block was translocated from its typical position to the CR downstream region, and the translocated trnH became a pseudogene. The position of the trnH pseudogene is consistent with the translocated trnH position reported in Odorrana. Consequently, the trnH rearrangement seems to be a common ancestry characteristic (synapomorphy) of Babina and Odorrana. Based on the "duplication and deletion" gene rearrangement model, a single genomic duplication event can explain the order of derived mt genes found in Babina and Odorrana.