Study On The Population Genetics Of Decapterus Maruadsi From The Northern South China Sea

Decapterus maruadsi is one of the important marine economic fishes,which is distributed in the coastal waters of China.The highest resource of it is in the northern South China Sea.In recent years,the fishing pressure around that area is increaseing,at the same time,marine ecology and environmental pollution are deteriorating seriously as well,which brings the results that the biological characteristics of D.maruadsi have changed significantly,and its resource has declined notablely.Therefore,there is an urgent need to conduct a research towards the genetic characteristics and germplasm resources of D.maruadsi in the northern South China Sea.In order to evaluate the genetic resources and analysis its genetic structure of the D.maruadsi population systematically and comprehensively in the northern South China Sea,the SLAF-seq technology will be used for the first time in this study to develop D.maruadsi microsatellite markers,and population genetics analysis will be conducted on the 8 D.maruadsi populations in the northern South China Sea.This study will provide guidance and theoretical basis for the scientific protection and rational development of D.maruadsi resources.The main results of the study are as follows:(1)Based on the SLAF-seq technology,a total of 28905 microsatellite markers(mono-to hexanucleotide repeats)were obtained in the genomic DNA of D.maruadsi,of which mono-nucleotide repeats was 8138(28.15%),di-and tri--nucleotide repeats were 13590(47.02%)and 5727(19.81%),respectively;tetra-to penta-nucleotide repeats were relatively few with respectively 1104(3.82%),234(0.81%)and 112(0.39%).In these loci,225 di-to penta-nucleotide repeats loci were randomly selected,and finally 80 polymorphic SSR loci were successfully screened.(2)A total of 1086 alleles were amplified from 80 SSR loci in 32 D.maruadsi individuals of Shantou,Guangdong.The number of alleles(Na)at each locus was 4?19(mean 14).Observed(Ho)and expected heterozygosity(He)were 0.2333?1.0000(mean 0.7038)and 0.3735?0.9588(mean 0.8370).78 of the 80 loci were highly polymorphic(PIC?0.5),and 2 were moderately polymorphic(0.25<PIC<0.5).24 loci significantly deviated from Hardy-Weinberg equilibrium(HWE),and showed high inbreeding coefficient(Fis=-0.5789?0.6823)and null allele frequency(Fua=-0.2087?0.2982).(3)Cross-species amplifications discovered a total of 70(87.50%),63(78.75%),58(72.50%),47(58.75%)and 36(45.00%)out of 80 loci of were successfully across in Decapterus macarellus,Decapterus macrosoma,Decapterus kurroides,Trachurus japonicus,Selaroides leptolepis,respectively,which showed that the 80 SSR loci had the better versatility in the genus Cyprinus,the next was in T.japonicus,and in S.leptolepis was relatively low.(4)26 SSR loci with highly polymorphic were selected to analyze the genetic diversity and genetic structure of 244 individuals in 8 populations of D.maruadsi in the northern South China Sea.The average number of alleles(Na)and effective alleles(Ne)were 22.1923 and 8.2077,and the mean values of observed(Ho)and expected heterozygosity(He)were 0.7062 and 0.8427.The average polymorphic information content(PIC)was 0.8233,indicating that these loci had high polymorphism and middle to high resolution.In each population,the average number of alleles(Na)and effective alleles(Ne)ranged from 8.6538(BS)to 16.4231(BH)and from 5.8543(BS)to 7.5991(ST),the mean observed(Ho)and expected heterozygosity(He)were 0.6858(ST)? 0.7205(YJ)and 0.8085(SY)? 0.8372(ST),respectively.The mean value of polymorphic information content(PIC)ranged from 0.7585(BS)to 0.8098(ST),indicating that the 8 populations of D.maruadsi in the northern South China Sea have high genetic polymorphism and better germplasm resources.(5)The Fst analysis showed that there was significantly low genetic differentiation among East Guangdong(ST),West Guangdong(YJ),Sanya Offshore(SY)populations and between them with other five populaiongs(BH ? FCG ? BS ? BMJ ? WC)(Fst=0.00844?0.04542,P value was 0.00000?0.04505),while the genetic difference between 4 populations in the Beibu Gulf(BH,FCG,BS and BMJ)and WC population was not obvious(Fst=0.00048?0.00848,P=0.09009?0.79279),which indicated that there was an obvious genetic differentiation among the populations of East Guangdong,West Guangdong,Sanya Offshore populations,and the Beibu Gulf-Wenchang.Nei's genetic distance,UPGMA cluster analysis,AMOVA,and Structure analysis also showed that there were highly similar genetic components between the 4 populations of the Beibu Gulf with the Wenchang population,which can be classified as one group(the Beibu Gulf-Wenchang group).The three populations,including East Guangdong,West Guangdong,Sanya Offshore,have relatively large genetic differentiation with the Beibu Gulf-Wenchang group,which can be considered as 3 independent groups.The above analysis results suggest that the 8 D.maruadsi populations in the northern South China Sea can be divided into 4 groups,including East Guangdong,West Guangdong,Beibu Gulf-Wenchang and Sanya offshore.Those 4 groups can be regarded as 4 fishery resource management units.The research results can provide theoretical basis and basic data for fishery resource assessment and management.