Genetic variability assessed by microsatellites in the breeding populations of the shrimp Penaeus (Fenneropenaeus) chinensis in China

Four populations of the shrimp, Penaeus chinensis, selected for White Spot Syndrome Virus resistance in breeding programs were examined at eight polymorphic microsatellite loci to assess the levels of allelic diversity and heterozygosity, as well as differentiation among the populations. A total of 71 different alleles were found over all the loci. The total number of alleles per locus ranged from 5 to 16, with allele sizes ranging from 150 to 600 bp. The number of genotypes per locus ranged from 5 to 20. The average observed heterozygosities of the G05, G06, G07 and G08 populations were 0.6563, 0.6250, 0.6188 and 0.6188 over all the loci, respectively. The high heterozygosities were maintained through the generations, indicating that there was no significant loss of genetic variability in the breeding program. However, genetic differences among the four populations were detected based on the number of alleles per locus, the effective number of alleles, number of genotypes per locus, frequency of the most common allele, P values, Fst values and pairwise Fst values. The data showed that as time under selection increased, the differentiation between generations became less, and the variations in the genetic structures of the populations became smaller. The data suggests that there is no detectable change in gene frequencies or heterozygosity over the generations tested, implying that the loci have been unaffected by the selective pressures of culture or that these changes occurred early in culture and prior to G05 generation in culture.