| Schizopygopsis malacanthus chengi is the main local commercial fish,only distributed in the upper reaches of the Dadu River.In the past 20 years,22 cascade hydropower stations have been planned to be built in Dadu River.The expansion of riverside roads and scattered sand mining sites will cause damage to the ecological environment to a certain extent.In addition,excessive fishing has caused a significant decline in the number of indigenous fish such as S.malacanthus.In order to master the original genetic diversity data and establish special fish habitat reserves,it is very necessary to study the characteristics of population genetic diversity,degree of genetic differentiation,genetic structure of S.malacanthus in the undeveloped region of Dadu River.In this study,the four geographic populations of S.malacanthus,such as Jiaomuzu River(JMZ),Zequ River(ZQ),Ake River(AK)and Suomo River(SM)populations,were selected as the research objects in the upper reaches of Dadu River,using mitochondrial cytochrome b(Cytb)gene sequence and 8 microsatellite(SSR)markers to analyze the genetic diversity and population structure of S.malacanthus between two seasons.The results are as follows:In winter 2017,based on the mitochondrial Cytb gene sequence,32 haplotypes were detected in 96 S.malacanthus.The value of haplotype diversity(h)is 0.949(JMZ),0.926(AK),0.880(ZQ),0.343(SM)and the value of nucleotide diversity(π)is 0.2925(ZQ),0.0752(AK),0.0310(JMZ),0.0004(SM),respectively.The populations of ZQ,AK and JMZ belong to high haplotype diversity,high nucleotide diversity patterns,and have a rich level of genetic diversity.The SM haplotype diversity and nucleotide diversity levels are both low.Based on the results of microsatellite data,the microsatellite loci of the four S.malacanthus populations were highly polymorphic.Various genetic diversity parameters showed that the effective number of alleles(Ne=1.103),Shannon index(I=0.134)and expected heterozygosity(He=0.076)of the ZQ population were all at a high level,AK,JMZ and SM populations were second,while they were not obvious different.In spring 2018,24 haplotypes were detected in 76 S.malacanthus,and the haplotype diversity h was 0.956(AK)、0.833(ZQ)、0.786(JMZ)、0.246(SM),and the nucleotide diversity π was 0.0252(JMZ)、0.0139(AK)、0.0017(ZQ)、0.0003(SM).The populations of AK and JMZ belonged to the model of high haplotype diversity and high nucleotide diversity,while the ZQ population belonged to the model of high haplotype diversity and low nucleotide diversity,and the level of genetic diversity are all relatively rich.However,haplotype diversity and nucleotide diversity levels of the SM population were both low.In winter 2017,AMOVA analysis based on the mitochondrial Cytb gene sequence and microsatellite showed that genetic variation mainly occurred within the population(68.42%and 93%,respectively).The genetic differentiation index(Fst)was calculated between the two populations.Based on the mitochondrial data,except AK&JMZ samples showed a moderate degree of genetic differentiation(0.05<Fst<0.15),the other two populations showed larger or extremely large degree of genetic differentiation(Fst>0.15).Based on the microsatellite data,there was no significant degree of genetic differentiation between the other two populations,except SM between other populations had a moderate degree of genetic differentiation(0.05<Fst<0.15).In spring 2018,the genetic variation of maternal inheritance mainly occurred between populations(70.52%),while the genetic variation of nuclear inheritance mainly occurred within populations(93%).The genetic differentiation index(Fst)of the mitochondrial data between the two populations showed large or extremely large degree of genetic differentiation(Fst>0.15).The genetic structure analysis in winter 2017,the phylogenetic tree and haplotype evolution network diagram based on mitochondrial data both showed that the four S.malacanthus populations could be divided into three genetic groups,namely(partial ZQ population),(partial ZQ population)ZQ,AK and JMZ)and(SM population);Structure clustering and PCA analysis based on microsatellite data showed that SM populations were relatively independent and clustered together,while ZQ,AK and JMZ populations were clustered and they are obviously mixed.In spring 2018,the analysis based on mitochondrial data showed that the 4 S.malacanthus populations could be divided into 3 genetic groups,named(part of the AK population),(part of the AK,ZQ and JMZ)and(SM population).And structure clustering and PCA analysis showed the similar results as that in 2017.By comparing the results of two seasonal studies on genetic diversity,genetic differentiation and genetic structure of S.malacanthus population based on microsatellite and mitochondrial Cytb gene sequences,it was found that the results of the two seasonal studies were basically consistent.Although the results based on the two molecular markers are slightly different,the overall trend is consistent.Based on mitochondrial markers,the genetic diversity was relatively high in all the populations except the SM population,which had a low level of genetic diversity.And the genetic differentiations were obvious among the four populations.Microsatellite data also showed obvious genetic differentiation between SM and(ZQ,AK,JMZ),but no obvious genetic differentiation among ZQ,AK,JMZ populations.The four geographic populations was genetically grouped into three groups by two molecular markers,while microsatellites results showed more promiscuous in some groups than genetic analysis of mitochondrial data.The results also showed that the evolutionary speed of nuclear inheritance was not consistent with that of maternal inheritance.Normally,the evolutionary speed of maternal inheritance is higher than that of nuclear inheritance,so maternal genetic molecules are more influenced by geographical environment(eg:altitude,climate,etc.)than nuclear genetic molecules,which might be related to the partial diffusion of S.malacanthus. |
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