Thesis (M.Sc.)--Chulalongkorn University, 1998

Three microsatellite loci, CUPmo18, Di25, and Di27, were used to study on population genetics of the black tiger prawn (Penaeus monodon) by using Polymerase Chain Reaction (PCR). Genetic variation were examined in 5 geographic samples, three from the Andaman Sea (Satun, Trang, and Phang-nga) and two from the Gulf of Thailand (Chumphon and Trad). All microsatellite loci were shown to be highly polymorphic with number of alleles at each locus of 37, 34, and 32 alleles respectively. Population analyses based on 3 loci revealed heterozygosities between 0.66-0.80 and average alleles per locus were 22.23-26.33. The effective number of alleles suggested that Chumphon (17.57) has highest genetic variation followed by Trang (16.97), Trad (15.15), Satun (14.3) and Phang-hga (14.18) respectively. Gene frequencies of each population did not conform Hardy-Weinberg equilibrium due to significant excesses of homozygotes in all samples. However, segregation analysis of three loci using 20 progeny from a representative full-sib family revealed Mendelion segregation nature of these microsatellites. Significant difference in allele frequency distributions were found for the Andaman Sea and the Gulf of Thailand populations at the CUPmol18 and Di25 loci. At those loci, the two populations from the Gulf fo Thailand were also genetically distinct. Population structures of P.monodon were assessed using the hierarchical F-statistics. The average theta value among 5 samples across the three loci was 0.009 (95% CI : 0.0011 to 0.0175) suggested low level of population subdivision in Thai P.monodon. Nevertheless, the analysis of geographic heterogeneity and phylogenetic reconstruction using the Neighbor-joining approach divided 5 geographic P.monodon samples to three different gene pools constituting of Satun, Trang, Phang-nga (A), Chumphon (B) and Trad (C)