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 proteinencoding 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.
The mitochondrial (mt) genome of the bushveld rain frog (Breviceps adspersus, Brevicipitidae, Afrobatrachia) is the largest (28.8 kbp) among the vertebrates investigated to date. The major cause of genome size enlargement in this species is the duplication of multiple genomic regions. To investigate the evolutionary lineage, timing, and process of mt genome enlargement, we sequenced the complete mtDNAs of two congeneric rain frogs, B. mossambicus and B. poweri. The mt genomic organization, gene content, and gene arrangements of these two rain frogs are very similar to each other but differ from those of B. adspersus. The B. mossambicus mt genome (22.5 kbp) does not differ significantly from that of most other afrobatrachians. In contrast, the B. poweri mtDNA (28.1 kbp) is considerably larger: currently the second largest among vertebrates, after B. adspersus. The main causes of genome enlargement differ among Breviceps species. Unusual elongation (12.5 kbp) of the control region (CR), a single major noncoding region of the vertebrate mt genome, is responsible for the extremely large mt genome in B. poweri. Based on the current Breviceps phylogeny and estimated divergence age, it can be concluded that the genome enlargements occurred independently in each species lineage within relatively short periods. Furthermore, a high nucleotide substitution rate and relaxation of selective pressures, which are considered to be involved in changes in genome size, were also detected in afrobatrachian lineages. Our results suggest that these factors were not direct causes but may have indirectly affected mt genome enlargements in Breviceps.
Horizontal transfer (HT) of genes between multicellular animals, once thought to be extremely rare, is being more commonly detected, but its global geographic trend and transfer mechanism have not been investigated. We discovered a unique HT pattern of Bovine-B (BovB) LINE retrotransposons in vertebrates, with a bizarre transfer direction from predators (snakes) to their prey (frogs). At least 54 instances of BovB HT were detected, which we estimate to have occurred across time between 85 and 1.3 Ma. Using comprehensive transcontinental sampling, our study demonstrates that BovB HT is highly prevalent in one geographical region, Madagascar, suggesting important regional differences in the occurrence of HTs. We discovered parasite vectors that may plausibly transmit BovB and found that the proportion of BovB-positive parasites is also high in Madagascar where BovB thus might be physically transported by parasites to diverse vertebrates, potentially including humans. Remarkably, in two frog lineages, BovB HT occurred after migration from a non-HT area (Africa) to the HT hotspot (Madagascar). These results provide a novel perspective on how the prevalence of parasites influences the occurrence of HT in a region, similar to pathogens and their vectors in some endemic diseases.
Sichuan torrent frog, Amolops mantzorum (family Ranidae, suborder Neobatrachia), possesses heteromorphic sex chromosomes unusual characteristics among amphibians. We determined the complete nucleotide sequence of the A. mantzorum mitogenome. This genome is 17,744 bp in length and contains 37 genes, 1 control region, and 1 light strand replication origin typically found in vertebrate mtDNAs. In the A. mantzorum mitogenome, a novel gene arrangement is observed within the WANCY tRNA gene cluster region. This mt gene arrangement seems to be usable as a molecular maker to distinguish to this species from other species in the genus Amolops.
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