Comparative Mitochondrial Genomics And Phylogeny Of Schizothoracinae And Barbinae

There has been academic controversy about the classification system and status of Schizothoracids.In fact,because of the functional differences of different genes,they may have undergone different intensitites of natural selection in the long history.This had led to the use of different genes in the analysis of molecular phylogeny to obtain completely different gene trees.In addition,too few or unrepresentative groups in the analysis can also affect the inference of the final results.With the development of largescale genome sequencing projects and the sharing of data,we could include more fish species for mitochondrial genome analysis.In this study,13 protein coding genes(13PCGs)and two rRNA genes in the mitochondrial genome of Schizothoracinae and Barbinae species in GenBank database were analyzed by maximum likelihood method and bayesian inference.The phylogenetic relationships of Schizothoracinae fishes were reconstructed by using single gene and multi-gene data sets,multi-partition and singlepartition strategies.Furthermore,the phylogenetic relationship and the time to most recent common ancestor(tMRCA)of the main groups were estimated.Combined with the geographical history and geological evidence of the distribution area,the evolutionary history and origin time of Schizothoracids group were inferred.Based on the data of single gene,the phylogenetic performance of Schizothoracinae and Barbinae fishes were also compared and evaluated.The results suggest that the consistency probability between maximum likelihood(ML)tree and bayesian inference of phylogenetic(BI)tree is very high when the single-partition strategy is used to construct the phylogenetic tree.However,the consistency between the ML tree and the BI tree constructed by the multi-partitioning strategy is low.Just from the perspective of multi-partition strategy,gene based multipartition strategy did not provide substantial help for solving phylogenetic relationship problem of Schizothoracinae and Barbinae fishes.Gene partitioning strategy can not only increase the search time,but also produce unstable tree structure.Among the phylogenetic relationships based on single gene construction,12S rRNA,ND2 and ND4 genes were relatively effective in distinguishing the upper family taxons.12S rRNA,16S rRNA,ND1,ND2 and ND5 genes could correctly determine the status of Schizothoracids in Barbinae fishe,while 12S rRNA,COX1,COX3,CYTB,ND1 and ND5 genes could correctly distinguish the tribes of Schizothoracids.Schizothoracinae is closely related to Barbinae fishes at the molecular level.Schizothoracinae and Percocypris which is a genus of Barbinae share a common ancestor.They both originated from some fishes of ancestor Barbinae fishes.Schizothoracinae species in "specialized" group and "highly-specialized" group are merged into Schizopygopsini tribe,and the "primitive " group and Percocypris are merged into Schizothoracini tribe.Schizothoracids group is a relatively young group in the subfamily Barbinae.It can not explain the relationship between the genus Percocypris and the primitive" group only from the morphological point of view.The whole Schizothoracinae fishes does not a monophyletic group.In the evolutionary relationship with time scale constructed by single gene,the differentiation time inferred from CYTB?ND5?ND1 gene and 13PCGs combined gene is relatively close.Schizopygopsini tribe and Schizothoracini tribe originated in the middle Miocene about 13 Ma ago,the NS normal fault system of the plateau formed in the late post collision period of the Indian and Eurasian plates,and the rain shadow effect of the rapid Himalayan formation in the middle Miocene on the central part of the plateau resulted in the origin of the Schizopygopsini tribe and Schizotheracini tribe.The present "primitive" group originated about 5 Ma ago(Pliocene),while the Schizothoracini tribe began to differentiate at 9.94 Ma.The "highly-specialized" group originated at 5.4 Ma.The differentiation and breeding events of each grade are related to the stage evolution of the Tibetan Plateau and global climate fluctuations.