| Schizothoracids,also known as schizothoracids,is a carp fish,S.prenanti is an important protected fish in Sichuan Province,and is also one of the endemic fish in the upper reaches of the Yangtze River in China with high academic and economic value.It is necessary to study the genetic diversity,degree of genetic differentiation and genetic structure of S.prenanti,from the undeveloped watershed of the Dadu River to grasp the original data of genetic diversity of endemic fish in the basin and establish a protected area for endemic fish habitat.In this study,four molecular markers,such as mitochondrial Cyt b,D-loop region and nuclear gene Rag2,S7,were used to analyze the genetic diversity,population differentiation and population history dynamics of the Zequ River(ZQ),Ah Ke River(AK),Marqu River(MEQ),and Zumuzu River(ZMZ)in the middle reaches of the Jinsha River and the upper reaches of the Dadu River(AH),and the advantages and disadvantages of the four molecular markers were compared.Based on mitochondrial Cyt b results,Cyt b gene of S.prenanti contained 89 mutation sites,with a total mutation rate of 9.74%,including 19 parsimoniously informative sites and 70 singleton sites.A total of 44 haplotype diversity were detected in190 samples,and the haplotype diversity(h)range is 0.238-1.000,as wel as the nucleotide diversity(π)range is 0.00169-0.24293.The populations of S.prenanti from ZQ,AK and AH all belong to the high h and high π modes,while the ZMZ and MEQ populations belong to the low h and low-π mode.The relationship diagram of the evolutionary tree and Network4.6 haplotype network constructed based on haplotypes showed that the populations of S.prenanti from MEQ,ZQ,AK and ZMZ originated from the same haplotype,and diverged on the basis of the ancestral haplotype with the influence of geographical environment factors.The neutral test and bifurcated point distribution analysis showed that the bifurcated point distribution map of the ZMZ and ZQ populations displayed an obvious single peak,and Tajima’s D and Fu’s Fs were both significant negative values,suggesting that the ZMZ and ZQ populations in this area may have expanded in the history.Compared with mitochondrial Cyt b,the results of mitochondrial D-loop region analysis showed that the mutation site,total mutation rate,parsimonic information site and single mutation site of the molecular marker were reduced.The overall number of haplotypes,haplodiversity range,nucleotide diversity range,and haplo-constructed evolutionary tree and Network4.6 haplotype network diagram were basically consistent with the results of Cyt b,that is,the four populations of the Dadu River were all evolved from an ancestral haplotype,although there was a certain degree of genetic differentiation,but there was still a close gene exchange relationship,while the AH population was an independent branch and had a large genetic differentiation with the four populations of the Dadu River.Based on the results of nuclear gene Rag2,the S.prenanti Rag2 gene contained 26 mutation sites,with a total mutation rate of 2.91%,including 7 parsimoniously informative sites and 19 singleton sites.A total of 45 haplotypes were detected in 190 samples,with the h range of 0.368-1.000 and the π range of 0.00063-0.03916.Both AH and ZMZ populations showed the mode of high h and high π,while AK and MRQ populations showed high h and low π mode,and only ZQ population showed a mode of low h and low π.The negative values of Tajima’s D and Fu’s FS of the ZMZ population were significant,and its bifurcated point distribution map showed obvious unimodal distribution,suggesting that the ZMZ population may have expanded historically.Compared with the nuclear gene Rag2,the analysis results of S7 gene showed that the total mutation rate,parsimonic information site and single mutation site of the molecular marker were reduced,while the number of haplotypes was increaseed.The analysis results of neutral test and bifurcated point distribution were basically consistent with the results of Rag2.That is,the five geographic groups have high genetic diversity,but the AH group has several exclusive haplotypes,and the phylogenetic tree and haplotype network diagram also have independent branches,and there is obvious genetic differentiation between the four geographic groups in Dadu River.There was a certain degree of gene mobility among the four geographical groups of Dadu River,,,and the degree of genetic differentiation was not large.The phylogenetic tree and haplotype network map were also mixed with each other,and there might be gene homogenization among them.The results were consistent with those of mitochondrial Cyt b and D-loop region.Analysis of mutation sites based on the gene sequnce of S.prenanti showed that Cyt b gene had the largest number of mutations(up to 89),followed by the D-loop region,more than S7 gene and Rag2 gene(19),which means that the two molecular markers of mitochondria were more suitable for calculating the genetic diversity of schizostoma genome.Although mitochondrial genes and nuclear genes did not show completely inconsistent results,they revealed a clear correlation between genetic differentiation,phylogenetic relationships and geographical barriers between the Ahai and Dadu River populations.In addition,based on the phylogenetic tree and Network4.6 haplotype network diagram,the author believes that mitochondrial Cytb marker is more suitable than D-loop markers in explaining population genetic structure,phylogenetic geographic pattern and population expansion.In this study,the genetic diversity,genetic differentiation degree and genetic structure were used to reveal the genetic information of S.prenanti groups in the middle reaches of the Jinsha River and the upper reaches of the Dadu River.The results not only help to understand the adaptation potential and population development trend of fish from Schizothorax in the basin,but also provide data support for the protection of the Schizothorax fish in the basin. |
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