| Procambarus Clarkii belongs to Arthropoda,Crustacea,Decapoda,Cambaridae,Procambarus.It is widely distributed in China and is one of the varieties with good breeding prospects in the freshwater aquaculture industry.P.clarkii has been cultivated in China since 1970,but in recent years,the germplasm of P.Clarkii has deteriorated,including early maturity,smaller size,low commodity rate and decreased disease resistance,which greatly affected the benef ITS of P.clarkii breeding industry.In order to achieve sustainable development of P.Clarkii aquaculture,it is urgent to carry out resource conservation and genetic improvement for P.Clarkii.In this study,we used four cultivated population(JS,HB,SC and MX)of P.clarkii to study influence of morphological traits on body weight,morphological difference analysis,genetic diversity and genetic structure based om Morphology and Molecular Biology in order to provide theoretical foundation for breeding fine varieties of P.clarkii.1.Effect of morphological traits on body weight in four cultivated population of Procambarus ClarkiiA total of 25 morphological characters were measured for the descriptive statistical analysis,simple correlation analysis,path analysis,determination coefficient analysis,multiple regression analysis and multiple correlation analysis to study the effect of 24 indexes on the body weight of P.Clarkii.Descriptive statistical results show that the morphological traits with the highest coefficient of variation in the other three breeding populations(SC,JS and HB)but except MX were all body weight,whose coefficient of variation was 18.209%,21.687% and 28.529%,respectively.The simple correlation analysis showed that the correlation analysis of each morphological character to the body weight of the four cultivated populations reached a significant level(P<0.01).The Path analysis showed that there were 5,3,6and 5 morphological traits respectively in the populations of MX,SC,JS and HB which were obvioualy correlated with the body weight of individuals in P.Clarkii,including the length,width and height of carapace in common in the 4 populations.The sum of the determination coefficient of individual trait and the co-determination Coefficient of two traits in each population was greater than 0.85,which indicated that the retention trait was the key index affecting the quality of each population,which can provide some reference value for artificial breeding of fine varieties.2.Study on morphological differences among four cultivated populations in Procambarus ClarkiiIn the study,the cluster analysis,principal component analysis,discriminant analysis and single factor analysis of variance were used to study the morphological differences of four cultivated populations of P.Clarkii.Cluster analysis showed that the four population clustered into two clades,and JS population showed the greatest morphological difference from the other three population and became an independent branch;eight principal components were obtained by principal component analysis,and their contribution rates were 22.172%,9.688%,8.296%,7.811%,7.351%,7.263%,6.750% and 6.729%,respectively.Among them,PC1 mainly reflected the head breastplate and thoracic appendage of P.Clarkii.;The discriminant function coefficients of 10 proportionate traits were obtained by discriminant analysis,and the discriminant functions of 4 breeding populations were constructed respectively,and the comprehensive discriminant rate reached 73.13%;The results of one-way analysis of variance showed that There has already been a big morphological difference in JS,the coefficient of difference between the two populations was less than 1.28,indicating that the morphological differences among each population had not reached the level of subspecies.3.Genetic diversity analysis of Procambarus Clarkii population based on Mitochondrial COI gene.The genetic diversity of four cultivated populations of P.Clarkii was studied by COI.The results showed that a total of 23 nucleotide mutation sites were detected at1168 bp,among which the transition site 15 was qualified and 8 transposition sites were found.The contents of T,C,A and G were 41.7%,12.5%,25.5% and 20.3%,respectively,and the content of AT(67%)was higher than that of GC(32.8%).A total of 21 haplotypes were defined in 136 individuals from 4 cultivated populations.The total haplotype diversity,mean number of nucleotide differences and nucleotide diversity were 0.6430,1.5829 and 0.0014,respectively,indicating low genetic diversity.The haplotype diversity index of the four populations was 0.4084 ~0.7652,and the nucleotide diversity was 0.0006~0.0019.JS population had rich genetic diversity and certain breeding potential,so it could be used as a good breeding material.However,the genetic diversity of SC population was low,so inbreeding should be avoided in subsequent breeding.The results of AMOVA analysis showed that within populations molecular variation accounted for 94.5%,among populations accounted for 5.5%,within populations genetic differentiation coefficient Fst = 0.055(P<0.01)(0.05< Fst <0.15),there was a moderate degree of genetic differentiation among populations.The NJ phylogenetic trees of 21 haplotypes from 4 cultivated populations were constructed by K-2P model.The haplotypes didn’t cluster according to the classification of the population to which the haplotypes belonged,and the complex cluster groups were formed by the interlusion of individuals from different populations.4.Genetic Structure analysis of Procambarus Clarkii population based on ITS1 sequence of nuclear geneThe first internal transcriptional spacer(ITS1)sequences of four cultivated populations of P.Clarkii were analyzed by direct DNA sequence measurement,and the existing crustacean homologous sequences from Genkbank database were used for systematic analysis.The results showed that the contents of T,C,A and G were 22.5%,26.8%,23.6% and 27.2%,respectively,and the content of AT(46.1%)was higher than that of GC(54%).The length of ITS1 was 838~860 bp,a total of 26 haplotypes were defined by 137 individuals.The total haplotype diversity,mean number of nucleotide differences,and nucleotide diversity were 0.6225,1.2017,and 0.0015,respectively,indicating low genetic diversity.Jiangsu population has high genetic diversity and can be used as good parents among four cultivated population.The results of AMOVA analysis showed that among populations genetic differentiation was Fst =0.03984(P<0.01)(0< Fst <0.05),indicating that genetic differentiation between populations was weak,which was different from that of mitochondrial COI gene,which indicated that there was moderate genetic differentiation between populations,which may be caused by molecular markers of two different evolutionary rates and genetic patterns.In summary,JS population has greater morphological differences than the other three populations,andthe genetic diversity of JS population is high,which can be used as the basic population for variety breeding.However,the genetic diversity of SC breeding population is poor,and there may be serious bottleneck effect and inbreeding decline.It is suggested that the number and range of introduced species should be increased in the late stage to reduce the risk of genetic diversity decline due to bottleneck effect and inbreeding decline. |
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