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

Abstract

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.

Keywords: Tylototriton broadoridgus; Tylototriton gaowangjienensis; mitochondrial genome; mitogenome; phylogenetic relationships.

Figure 1

Gene maps of the two newly sequenced Tylototriton species.

Figure 2

GC and AT skews of mitochondrial PCGs of T. broadoridgus and T. gaowangjienensis.

Figure 3

Relative Synonymous Codon Usage (RSCU) of mitogenomes of T. broadoridgus and T. gaowangjienensis.

Figure 4

The Ka/Ks ratio of 13 PCGs among 12 species of Tylototriton.

Figure 5

Phylogenetic relationships within Salamandridae derived from ML method based on 13 PCGs. Note: Names in red show the phylogenetic positions of T. broadoridgus and T. gaowangjienensis that we sequenced in this study. The numbers on the nodes are the bootstrap values and posterior probabilities from ML and BI methods. The GenBank accession number of each species is given in the bracket after the species name.