Studies On The Molecular Phylogeny And Biogeography Of Gammaurs In Xinjiang Uygur Autonomous Region(China)

The genus Gammarus belonging to the family Gammaridae,Amphipoda,is distributed in Eurasia and North America,and is one of the most diverse crustacean genera.Until now,over 200 species have been reported in the literature.Xinjiang Uygur Autonomous Region is located in the hinterland of Eurasia and situated between the most abundant freshwater diversity habitats of the Gammarus,that is,Lake Baikal and Ponto-Caspian basin.However,there are few studies focusing on the Gammarus in Xinjiang Uygur Autonomous Region.Previous studies were mainly based on morphological studies,and relevant molecular studies were incomplete,and none of them included the new species described in recent years because of the limitations of early time.Therefore,it is necessary to conduct molecular phylogeny and biogeography research to the Gammarus in Xinjiang Uygur Autonomous Region.This study systematically summarized the morphological characteristics and geographical distribution of Gammarus in Xinjiang Uygur Autonomous Region.Two mitochondrial genes(COI,16S)and three nuclear genes(18S,28 S,EF1?)were used to construct a phylogenetic tree of Gammarus in Xinjiang Uygur Autonomous Region,and the effectiveness of each species was analyzed.This study also reconstructs the ancestral distribution area of Gammarus in Xinjiang Uygur Autonomous Region,and discusses their origin and evolution.The main research results are as follows:1.A new species of Gammarus zhouqiongi sp.n.was described in detail.The characteristics of the new species were drawn and the key to the Gammarus in Xinjiang Uygur Autonomous Region was compiled.There are a total of 9 species of the genus Gammarus in Xinjiang,distributed in both southern and northern Xinjiang,concentrated in the cross-border rivers such as Irtysh River,Emin River and Ili River basin in the western part of Xinjiang Uygur Autonomous Region.2.In addition to the analysis of no molecular data of G.simplex,the analysis of interspecific and intraspecific genetic distances based on the mitochondrial COI gene showed that the interspecific genetic distances of the Gammarus were 0.16-0.37 and the intraspecific genetic distances were 0.00-0.05.Phylogenetic analysis of 8 species in Xinjiang(except Gammarus simplex)based on mitochondrial genes(COI and 16S)and nuclear gene(18S,28 S and EF1?)joint gene sequences by bayes method and maximum likelihood method showed that different species have their own branch,the height of the single system fully supports the validity of the species.3.The phylogenetic tree with molecular clock constructed by the combined genes showed that the first divergence of the Gammarus appeared at about 24 Ma,and the middle and late Miocene at about 10 Ma was an important stage for the species formation of the Gammarus.At about 8 Ma,all the species in the genus were formed,and different geographical populations of each species were formed at about 2 Ma.4.Ancestors area reconstruction results show that the Junggar basin,the Tarim basin,the Ili valley and Emin basin may have to be a common ancestor of Xinjiang Gammarus distribution.It is speculated that the first great uplift of the Qinghai-Tibet Plateau and the extinction of the Paratethys led to the westward spread of ancestors of some species of Gammarus,and the genus Gammarus in Xinjiang appeared divergent for the first time.The second and third great uplifts of the Qinghai-Tibet Plateau and the accompanying great climatic changes led to the further differentiation of species in the genus Gammarus in Xinjiang and the basic formation of each species during this period.Finally,the 4th Great Uplift of the Qinghai-Tibet Plateau and the Quaternary Glaciation,two geological events,contributed to the formation of different geographical populations of Gammarus.