Genetic Diversity And Structure Of Glyptothorax Sinensis In Upper Yangtze River

The upper reaches of the Yangtze River are rich in biodiversity and an ecologically sensitive area inhabited by endemic fishes.Glyptothorax sinensis belongs to order Siluriformes,family Sisoridae and genus Glyptothorax.It is a small benthic fish which has a high dependence and adaptability to the living environment and are widely distributed.It can live in alpine valley rivers also in plain lakes and rivers so that form different ecological groups,is a good object to study biogeography and environmental adaptability.In recent years,the development of hydroelectric cascades in the upper reaches of the Yangtze River has resulted in the shrinking and fragmentation of fish habitats,which have had a significant impact on their habitats and natural resources.The study of genetic diversity and genetic structure is helpful for the formulation of germplasm resources assessment and protection measures.In this study,a total of 341G.sinensis were collected from the main stream of the upper reaches of the Yangtze River[Banan（BN）,Jiangjin（JJ）,Hejiang（HJ）,Luzhou（LZ）,Nanxi（NX）],Minjiang[Qianwei（QW）],the middle reaches of the Jinsha River[Panzhihua（PZH）],the lower reaches of the Jinsha River[Qiaojia（QJ）]and the tributaries of Heishui River[Ningnan（NN）]in2017-2018.The mitochondrial DNA and microsatellite DNA were used to assess population genetics,and the main results were as follows:1. The mitochondrial cytochrome b（cyt b）、Cytochrome c oxidase subunit I（COI） sequences were used to analyze a total of 341 samples from 9 populations in the upper reaches of the Yangtze River,the Minjiang River,the middle reaches of the Jinsha River,the lower reaches of the Jinsha River,and the tributary Heishui River.The results showed that a total of 80 mutation sites were identified from cyt b sequence,which defined 65haplotypes.The haplotype diversity（H_d）and nucleotide diversity（P_i）was 0.845 and0.007,respectively.Thirty-one mutation sites were found in the COI sequence,which 23defined haplotypes,and the H_d and P_i were 0.774 and 0.005,respectively.Overall,it showed a high level of genetic diversity and the genetic diversity of Jinshajiang population（H_d:0.453,P_i:0.003）was relatively low.Analysis of molecular variance（AMOVA）showed F_ST﹥0.5,which indicated that significant population genetic differentiation had occurred among G.sinensis populations.Pairwise AMOVA showed that there was no population genetic differentiation between populations from the the upper Yangtze River and the Minjiang River,however,significant differentiation between them and the rest populations from Jinsha River.The NJ phylogenetic tree,the haplotype network and the group STRUCTURE analysis revealed three haplotype clades with high resolution.They are the middle reaches of jinsha river（PZH）,the lower reaches of jinsha river（QJ、NN）and the upper reaches of Yangtze river（BN,JJ,HJ,LZ,NX,QW）respectively.BSP analysis showed that a population expansion event occurred during the late Pleistocene（0.13-0.01Ma）in the upper reaches of the Yangtze River bream.It’s the same to the lower reaches of the Jinsha River at 0.0125-0Ma,later than Yangtze River group.2. A total of 29 polymorphic satellite loci were developed based on restriction site associated DNA（RAD）data,which have been used test genetic diversity in one population of 24 individuals.The average number of alleles（Na）was 14,and the average expected heterozygosity（He）and observed heterozygosity（Ho）were 0.900 and 0.619,respectively.The mean polymorphic information content（PIC）was 0.868,ranging from0.701 to 0.943.Ten pairs high polymorphism markers were selected to genotype a total of 160 samples from 8 populations to analyzes genetic diversity and genetic structure.The results showed that the average Na ranged from 8.7 to 16.1,and the average Ne from6.714 to 10.971.The average Ho was 0.297-0.503,and the He from 0.907 to 0.939.It indicated that the genetic diversity of G.sinensis population was at a high level.The F_STindex and AMOVA analysis showed that there was no genetic differentiation among the five populations in the Yangtze River,however obvious differentiation between populations from the Upper Yangtze River（JJ,HJ,ZL,NX,QW）and from Jinsha River population（QJ,NN,PZH）.Analysis of PCo A and STRUCTURE supported the result of AMOVA analysis that populations from the upper reaches of the Yangtze River and the Jinsha River formed different clades.Based on mitochondrial and microsatellite molecular markers,this study showed that the high level of genetic diversity for G.sinensis in the upper reaches of the Yangtze River,and genetic differentiation occurs among the populations.It is suggested the population in the middle reaches of Jinsha River,the lower reaches of Jinsha River and the upper reaches of Yangtze River should be protected as three significant evolutionary units（ESU）.Due to the low genetic diversity of populations in Qiaojia,Ningnan and Panzhihua sections,special attention should be paid to the development of hydropower projects in Jinsha River.