Phylogenetic Analysis Of The Tylototriton Verrucosus Group Based On The Mitochondrial Genome

The genus Tylototriton Anderson 1871,which belongs to family Salamandridae,order Caudata.This genus is the endemic groups of Asia and mainly distributed in South,Southeast and East Asia.Due to some species of Tylototriton are very similar in morphology,therefore leads to the debates of classification as well as phylogeney.Mitochondrial genome has the characteristics of fast evolutionary rate,no duplicate copies of the same gene,maternal inheritance,small in size,and so on,which is a useful marker system in numerous phylogenetic analyses of amphibian relationships.In this study,we determined the complete mitochondrial genomes sequences of nine individuals in eight Tylototriton species by PCR,which are T.wenxianensis,T.taliangensis,T.pseudoverrucosus,T.yangi,T.kweichowensis,T.shanorum,T.shanjing and two T.verrucosus.We analyzed the structure characteristics of the mitogenomes,and combined with the mitochondrial genome sequence of the other 38 species of Caudata from GenBank to explore the phylogenetic relationship and evolution of Tylototriton.The main results summarized as follow:1.The structure characteristics of the mitogenomes of nine Tylototriton speciesIn this study,the length of complete mitochondrial genome of nine Tylototriton ranged from 16,265 bp to 17,096 bp,which the gene composition and arrangement of genome were identical as mostly vertebrate mitogenome.The higher A+T content in mitogenomes of Tyototriton.The mostly protein-coding genes used ATG as the start codon and only COI used GTG,however,the stop codon including complete stop codon TAA,TAG,AG A and incomplete stop codon T.All tRNA genes,except for tRNAser(AGY)was lack of dihydrouracil loop,were folded into typical clover-leaf structures.A noncoding-sequence region of different lengths between tRNAThr gene and tRNAPro gene had been found in all mitogenomes of Tylototriton,and that was specific in caudate mtDNAs.We also found the noncoding-sequence and adjacent genes constitute tandem repeat structure in mitogenomes of T.yangi,T.kweichowensis,T.shanorum,T.shanjing and two T.verrucosus,and the species of possessing the repeats were gathered a monophyletic group in the phylogenetic analysis,that maybe hint a single origin of the repeat sequences.2.The phylogenetic relationship of TylototritonWe reinvestigated the phylogenetic relationships of the Salamandridae with all protein-coding genes of mitochondrial genome by Bayesian inference and Maximum Likelihood.The results showed the genus Salamandrina was first separated from the others,and followed by true Salamanders,primitive newts and modern newts(including modern European newts,modern Asian newts and other newts of living in Europe).The species of Tylototriton formed a monophyletic and that was sister taxon with genusEchinotriton.Within Tylototriton,it splits into two main clades in this study,one clade called as the T.verrucosus group and the other clade called as the T.asperrimus group.In the clade of T.verrucosus group,the species distributed in southern Sichuan(T.pseudoverrucosus and T.taliangensis)that gather a clade was rooted,and the other collected from Yunnan of China and Myanmar(T.yangi,T.verrucosus,T.shanjing,T.kweichowensis and T.shanorum)form another clade.In addition,the results of interspecific genetic distance and phylogenetic showed that the T.verrucosus from Longchuan and T.shanjing from Dali maybe the same species in this study.3.The origin and migration of TylototritonWe performed divergence time estimation analyses of the Salamandridae based on all protein-coding genes sequence of mitogenomes by relaxed clock method.Our results supported that Salamandridae originated in Europe and probably in Late Cretaceous(67.9 May).The Tylototriton probably dispersed to Asia from Europe after disappearance of the Turgai strait in Late Oligocene(29.0 Mya)and then through the West Asia along the Himalayas mountains moved to Southeast Asia.