Two Complete Mitochondrial Genomes of Leptobrachium (Anura: Megophryidae: Leptobrachiinae): Characteristics, Population Divergences, and Phylogenetic Implications.

The mustache toads Leptobrachium boringii and Leptobrachium liui are two attractive species in Megophryidae, in which adult males have mustache-like keratinized nuptial spines on their upper lip. However, both are under threat due to multiple factors, of which scientific studies are still very limited. In this study, two new complete mitochondrial genomes of L. boringii and L. liui were sequenced, assembled, and annotated based on next-generation sequencing. The mitogenome lengths of L. boringii and L. liui were found to be 17,100 and 17,501 bp, respectively, with both containing 13 protein coding genes, 23 tRNAs, 2 rRNAs, and 1 non-coding control region. Nucleotide diversity analyses indicate that atp8, atp6, and nad2 showed higher nucleotide diversity than cox1, cox3, and cytb. The intraspecific genetic distances among three different populations of L. boringii exceed 4%, and those between two populations of L. liui reach 7%. Phylogenetic relationships support their division into two subfamilies of Megophryidae (Leptobrachiinae and Megophryinae) as well as two species groups within Leptobrachium, corresponding to the number of keratinized nuptial spines (10-48 in the L. boringii species group vs. 2-6 in the L. liui species group). The two new mitogenomes reported in this study provide valuable data for future molecular evolutionary and conservation studies of the genus Leptobrachium and other Megophryidae toads.

Characterization, Comparison of Two New Mitogenomes of Crocodile Newts Tylototriton (Caudata: Salamandridae), and Phylogenetic Implications.

Mitochondrial genomes (mitogenomes) are valuable resources in molecular and evolutionary studies, such as phylogeny and population genetics. The complete mitogenomes of two crocodile newts, Tylototriton broadoridgus and Tylototriton gaowangjienensis, were sequenced, assembled, and annotated for the first time using next-generation sequencing. The complete mitogenomes of T. broadoridgus and T. gaowangjienensis were 16,265 bp and 16,259 bp in lengths, which both composed of 13 protein-coding genes (PCGs), 2 rRNA genes, 22 tRNA genes, and 1 control region. The two mitogenomes had high A + T content with positive AT-skew and negative GC-skew patterns. The ratio of non-synonymous and synonymous substitutions showed that, relatively, the ATP8 gene evolved the fastest and COI evolved the slowest among the 13 PCGs. Phylogenetic trees from BI and ML analyses resulted in identical topologies, where the Tylototriton split into two groups corresponding to two subgenera. Both T. broadoridgus and T. gaowangjienensis sequenced here belonged to the subgenus Yaotriton, and these two species shared a tentative sister group relationship. The two mitogenomes reported in this study provided valuable data for future molecular and evolutionary studies of the genus Tylotoriton and other salamanders.