A Study On Genetic Diversity Between Yangtze River Wild & Domestic Populations Of Silver Carp And Bighead Carp Using Microsatellite Markers

Silver carp(Hypophthalmichthys molitrix C.et V) and Bighead carp(Aristichthys nobilis Richardson) are important pond-cultured fish species in our country,and they inhabit widely in the major river basins of China,including Heilong Jiang,Yangtze River and Pearl River.Among the three local populations,the cultured performance of Yangtze River wild population is the best.In recent years,the germplasm of wild silver carp and bighead carp has been endangered by environmental pollution,large-scale water conservancy construction.Under present cultured operation,the germplasm of domestic silver carp and bighead carp was degenerated seriously due to various improper breeding methods.As a result,the elite characters of wild fish have been attenuated severely. Furthermore,germplasm of the two fish was much more seriously imperiled,as domestic population jumbles wild population and the depravation of ecologicial enviroment. Thereby,it's particularly necessary to evaluate the genetic diversity and determine the genetic differentiation of silver carp and bighead carp.In this study,the genetic diversity of the two populations was studied using twenty-two microsatellite markers of silver carp designed by researchers in our research team and Ocean University of China.The results were as follows:(1) In the two silver carp populations,there was I monmorphic marker(BL12)in the two populations and the percentage of polymorphic loci was 95.45%.The total observed alleles number of the 22 microsatellite loci was 188,which varied from 2 to 12. The average of observed alleles number in the Yangtze River wild population and domestic population was 4.409 vs 4.136 respectively(P＞0.05);the average effective alleles number was 3.276 vs 3.034 respectively(P＞0.05);the average observed heterozygosity(Ho) was 0.744 vs 0.693 respectively(P＞0.05),and the average expected heterzygosity(He) was 0.612 vs 0.581 respectively(P＞0.05),and the average PIC was 0.569 vs 0.533 respectively(P＞0.05).The average Shannon's index was 1.180 vs 1.100 respectively(P＞0.05);the genetic distance and the genetic similarity coefficient were 0.280 and 0.756 respectively.Chi-square test was used to analyze the genotypes based on Hardy-Weinberg equilibrium;the P value showed most loci tested were according with Hardy-Weinberg equilibrium.Fst index showed that most variation came from individuals within population(92.33%) rather than ones among populations(7.67%). The genetic diversity of domestic population was depressed to a certain extent,but there was no obvious difference between the two populations. (2) In the two bighead carp populations,there were 3 monmorphic markers (BL12,BL83 and BL90) in the two populations and the percentage of polymorphic loci was 86.36%.The total observed alleles number on the 22 microsatellite loci was 162, which varied from 2 to 12.The average of observed alleles number in the Yangtze River wild population and domestic population was 3.727 vs 3.636 respectively(P＞0.05);the average effective alleles number was 2.927 vs 2.813 respectively(P＞0.05);the average observed heterozygosity(Ho) was 0.780 vs 0.778 respectively(P＞0.05),and the average expected heterzygosity(He) was 0.550 vs 0.540 respectively(P＞0.05),and the average PIC was 0.500 vs 0.487 respectively(P＞0.05).The average Shannon's index was 1.020 vs 0.986 respectively(P＞0.05);the genetic distance and the genetic similarity coefficient were 0.067 and 0.936 respectively.Chi-square test was used to analyze the genotypes based on Hardy-Weinberg equilibrium;the P value denoted that most loci tested were accorded with Hardy-Weinberg equilibrium.Fst index showed that most variation came from individuals within population(97.36%) rather than ones among populations (2.64%).One locus displayed lacking of heterozygote in the wild population,while all loci showed surplus heterozygote in the domestic population.These two populations were abundant in genetic diversity.(3) From the results of microsatellite markers analyzed,the wild population and domestic population of silver carp and bighead carp were both abundant in genetic diversity.The results showed that although artificial propagation process and human activity interference had changed the habitat,which caused the decrease in reproductive population and reduction in spawning stock and had influenced the genetic diversity of the two fish,the genetic diversity between the wild and domestic populations was no significant difference for the human's interferences activities.From this research,the wild and the domestic population of silver carp and bighead carp were both abundant in genetic diversity and breeding potential.They can be as good breeding material to selected breed and cultivate new varieties(lines),domestic populations should adopt scientific selection and breeding measures to maintain genetic diversity.