| The pearl oyster Pinctada fucata is one of shellfish for China’sproduction of seawater pearl, and the famous "south pearl" is produced byPinctada fucata. In this study, by using microsatellite markers to analysisthe genetic diversity of diallel crosses groups and two groups of differentgenerations families which built by our group, and analysis the correlationbetween genetic diversity of the groups and the families and performances.Finally, analysis the parental genetic background of the second groups of F2generation family, and further analysis the correlation between the parentalgenetic background with the offspring growth rate. The main results are asfollow:1. Genetic diversity of mass-selected populations. In this study,genetic diversities of the nine crosses of the purebreds (SS5, XX6, BB7)and the crossbreds (BX1, BS2, XB3, XS4, SX8, SB9) from Sanya (S), Xuwen (X) and Beihai (B) were investigated by using eight microsatellitemolecular markers primers which can be effectively amplified and showpreferably polymorphic. A total of48alleles were detected from445individuals. The observed allele number was2-10, average effective allelenumber was3.88-5.63, average observed heterozygosity was0.59-0.74,and average expected heterozygosity was0.65-0.75. The polymorphicinformation content (PIC) for the nine crosses were0.58-0.71, suggestingthat they are highly polymorphism (PIC≥0.5); Nine groups on the eightmicrosatellite loci significantly part of the pole deviated from the geneticbalance, seven groups exist to varying degrees heterozygous deletion;genetic differentiation between any two of the nine populations are-0.0104to0.1432, differentiation is not obvious.Among the nine crosses, thepurebred SS5had the highest polymorphism, and the crossbred SX8hadthe lowest. The results above provide useful information for the selectivebreeding and germplast conservation of P. fucata.2. Correlation between the genetic makeup and growth performancesof mass-selected populations. In order to explore the relationship betweenthe performances and genetic diversity, we investigated the relationshipbetween genetic structure and performances of nine diallel crosses of thepearl oyster Pinctada fucata using eight microsatellite loci. The resultsdemonstrated that there are relationships between performances in terms of daily shell length growth ratios (r) and mean numbers of alleles (A) andmean heterozygosities (H) over loci at population level, and mean numbersof alleles per locus (a) and the proportion of heterozygous loci (h) atindividual level, respectively. Among the relationships, A is negativelyweakly correlated with r (R2=0.2186) with linear regression equation: y=-0.0173x+0.2289while a, H and h are positively significantly correlatedwith r with correlation coefficients of R2=0.7443, R2=0.9321and R2=0.7443, and linear equations of y=0.4101x-0.5434, y=0.446x-0.1546and y=0.4101x-0.5434, respectively. It suggested that there existsignificant positive correlations between heterozygosities and traitsperformances in the pearl oyster P. fucata.3. Genetic diversity of selected families. Analysis the genetic diversityand genetic structure of Pinctada fucata two batches of12breedingfamilies by microsatellite. Eight pairs of microsatellite loci detected26alleles in12families, the average of each locus to obtain3.25alleles, theobserved allele number was1.75-2.88, average effective allele number was1.35-2.35, average observed heterozygosity was0.1700-0.5775, andaverage expected heterozygosity was0.2075-0.5991, average polymorphicinformation content was0.17to0.48, and Shannon’ s information indexwas0.3093~0.9114. A high degree of genetic differentiation between each family, and with the continuation of the generations, the geneticdifferentiation between adjacent generations may have decreased.4. Correlation between the genetic makeup and growth performancesof selected families. Eight pairs of microsatellite loci were used to analyzethe correlation between genetic diversity and performances of12Pinctadafucata families. The results demonstrated that the correlation between theparameters of mean numbers of observed alleles (Ao), effective alleles (Ae),observed heterozygosity (Ho), expected heterozygosity (He) andpolymorphic information content (PIC) and phenotypic parameterdisplayed a convex curve, suggesting that medium genetic parameters areconducive to pearl oyster family growth. In general, families with goodperformances have larger genetic diversity parameters.5. The correlations between the parental genetic makup and growthperformances of offspring. The correlation between the parental geneticmakeup and offspring’s growth performance of Pinctada fucata wasstudied using eight microsatellite loci. By using SPSS software, the resultsshowed that when genetic distances between parents ranging from0.5355to0.5696, they were significantly positively correlated with the growthperformances of the offspring; when ranging from0.6496to1.0000, theywere significantly negatively correlated with the offspring performances.When the average proportions of heterozygous loci over individuals in parents were ranged from0.3125to0.5000, they were highly significantlybut negatively correlated with the growth performances of the offspring;when ranging from0.5625to0.6250, they were significantly positivelycorrelated with the growth performances of offspring. When the averagenumbers of alleles over individuals per locus in parents were ranged from1.3125to1.5000, they were highly but negatively significantly correlatedwith the growth performances of the offspring; when ranging from1.5625to1.6250, they were significantly positively correlated with the growthperformances of the offspring. From above, it can be concluded that thehigher the proportion of heterozygous loci and the number of alleles overindividuals per locus in parents, the better the performances in the offspring,but the larger the genetic distances in the parents, the worse theperformances in the offspring, implying that the extent of genetic diversityin individuals is more closely related with traits performances. |
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