| Large yellow croaker(Larimichthys crocea),also known as yellow croaker,gold leaf fish,cucumber fish,yellow croaker,etc.It belongs to the class Chordropoda,the vertebrate subphyla,the Osteichthyes(Osteinchthyes),the Sphinoptera,the Perciformes,the Sciaenidae,and the Larimichthys,which are distributed in the offshore area of mainland China.Due to overfishing and environmental degradation,the number of wild yellow croakers has fallen sharply.In order to restore this traditional fishery resource,China's aquatic research workers have carried out a large number of artificial propagation and breeding of large yellow croaker,and Zhejiang,Fujian and other regions release tens of millions of artificial fry to natural sea areas every year.In recent years,the resources of large yellow croaker in natural sea areas have increased year by year,and significant economic,social and ecological benefits have been achieved.Therefore,it is necessary to evaluate the genetic impact of the proliferation and release of large yellow croaker on the wild large yellow croaker population.In this study,the external morphology and anatomical structure of large yellow croaker: brackish collateral,otolith structure,mitochondrial COI gene,Cytb gene and D-loop region,and microsatellite molecular markers were used to compare and analyze the germplasm differences and inheritance of large yellow croaker.Variation,with a view to providing a scientific basis for germplasm protection and resource management of large yellow croaker.The main findings are as follows:1.Morphological and molecular characteristics of different genetic groupsAccording to the resource survey,the anatomical characteristics of some wild croakers in Zhoushan do not completely match the anatomical characteristics of croakers in the existing taxonomic books,and the otolith morphology is also different from the original anatomical description.Therefore,by comparing the morphological differences between the wild population of Zhoushan large yellow croaker and the Fuding large yellow croaker,the descriptions of the lateral scales of the large yellow croaker and the branch of the swim bladder were revised and supplemented.The molecular identification results showed that the wild croaker in Zhoushan and the croaker in Fuding had the highest similarity and the closest relationship.2.Mitochondrial DNA marker analysisUsing different mitochondrial DNA molecular markers(COI gene,Cytb gene and D-loop region)to study 9 large yellow croaker populations,the results show that: in the obtained 454 bp COI sequence,there are 27 total mutation sites and 12 parsimony information sites Among them,the breeding population contains 10 mutation sites,and the wild population contains 23 mutation sites;in the obtained 741 bp Cytb sequence,there are64 total mutation sites and 34 parsimony information sites,of which the cultured population contains 20 mutation sites The wild population contains 62 mutation sites;in the805 bp control area,there are 126 total mutation sites,of which the breeding population contains 56 mutation sites and the wild population contains 113 mutation sites.In terms of base composition,the base composition of large yellow croaker has base bias,and the conversion ratio R is 2.1,41.6,and 8.7,respectively.In all samples,26 haplotypes were detected by the COI gene.The haplotype diversity was 0-0.92 and the nucleotide diversity was 0-0.005;0-0.54;73 and 97 haplotypes were detected in Cytb gene and D-loop region,and the diversity of cultured and wild haplotypes were(0-0.83,0-0.91)and(0.9-0.97,0.99-1).The UPGMA evolutionary tree shows that wild groups come together and farmed groups come together.The genetic differentiation between the large yellow croaker farming group and the wild group mainly comes from within the group.The genetic diversity of wild populations is higher than that of farmed populations,and the genetic diversity of farmed populations is at a low level,and there is significant genetic differentiation between wild population groups.Neutral test Tajima's D and Fu's Fs analysis found that wild large yellow croaker groups experienced rapid outbreaks and expansion events.It is also concluded that the mitochondrial D-loop region of Pseudosciaena crocea has higher sensitivity in the identification of intraspecies populations.3.Microsatellite DNA marker analysisUsing 16 self-developed large yellow croaker microsatellite primers,the genetic diversity,genetic structure and historical dynamics of 9 large yellow croaker populations were analyzed.Genetic diversity analysis results showed that 6 of the 16 loci were moderate polymorphic loci(0.25 <PIC <0.5),10 were highly polymorphic loci(PIC> 0.5),and the average observed heterozygosity was 0.56,The average expected heterozygosity was 0.61,7 sites were significantly off Hardy-Weiberg equilibrium,and 9 sites did not deviate from equilibrium.The number of alleles(Na),observed heterozygosity(Ho),allele abundance(Ar),expected heterozygosity(He),and polymorphic information content(PIC)in each group were highest in the ZS population and lowest in the DQZ population All of them deviate from Hardy Weinberg equilibrium,indicating that the genetic diversity of these 9 populations is at the upper middle level.AMOVA analysis showed that the genetic variation mainly came from within the population,and the genetic differentiation coefficient reached a significant or extremely significant level.The genetic distance results show that the genetic distance between DQZ and Z is the largest(D = 0.28,S = 0.781),and the genetic distance between D1 Y and ZS is the smallest(D = 0.020,S = 0.981).The UPGMA phylogenetic tree shows that DQZ and YD gather first for a large group,then the natural groups(ZS,D1 Y,GZY)are grouped together,Z,SC,D1,FD are grouped together,the Structure results also show similar results,the best K value is 2 or 5.The bottleneck effect results show that the effective population size(Ne)ranges from 8.1 to infinity.Overall,wild populations are likely to experience genetic bottleneck effects in the history,and the allele frequency distribution map is L-shaped. |
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