Parentage Determination and Effective Population Size Estimation in Mass Spawning Pacific Oyster, Crassostrea gigas, Based on Microsatellite Analysis

Seven high polymorphic microsatellite loci were used to determine the pedigrees in a mass spawning of Pacific oyster, Crassostrea gigas, and to estimate the genetic variability between broodstock and offspring. Parental assignment was performed on a total of 155 individuals, including 141 offspring, 8 candidate mothers, and 6 candidate fathers. The assignment results of real offspring were generally in agreement with simulation with a success rate over 99% using only six of these loci. The allelic diversity and observed heterozygosity (H-o) exhibited similarity between parents and offspring populations, but the expected heterozygosity (H-e) had a significant decrease in offspring. Although all the males and females contributed to the next generation, the variances of reproductive success and unequal sex ratio resulted in a decline in effective population size (N-e = 11.42). The inbreeding rate of this small-scale, mass spawning population was estimated at approximately 16.5% per generation. This gave us an insight that when designing breeding programs based on mass spawning for future oyster cultivation generations, the higher inbreeding and lower effective population size should be considered.