Analysis of genetic variation and inbreeding among three lines of hatchery-reared Crassostrea virginica broodstock

Abstract Eastern oyster, Crassostrea virginica, aquaculture is a rapidly growing industry in the US. Although selective breeding programs have successfully developed lines of C. virginica with faster growth and improved disease resistance for aquaculture, maintaining genetic diversity in hatchery stocks over successive generations remains a challenge. This study assessed the genetic effects of breeding practices on three lines of hatchery-reared C. virginica derived from wild North Carolina oyster populations that were spawned into multiple cohorts in three successive generations. Utilizing 22 microsatellite markers, parentage assignment was determined for three successive generations of hatchery-produced cohorts. Relatedness, allelic richness, heterozygosity, and genetic differentiation were compared among wild progenitor cohorts and hatchery-produced cohorts from the three lines. Although few crosses between siblings produced offspring that were used as broodstock, results revealed decreased genetic diversity in all three lines as evidenced by reduced allelic richness and increased relatedness in hatchery-produced cohorts when compared to wild progenitor cohorts. Percentages of inbred offspring increased with succeeding generations across the three hatchery-reared lines. Genetic differentiation gradually increased with subsequent generations of hatchery-produced cohorts within and between the three lines. Despite efforts to lessen inbreeding and loss of genetic diversity (equal contributions from single pairwise crosses), uneven performance of offspring make maintenance of genetic variation and control of inbreeding across generations difficult to achieve. Rebuilding genetic variation within lines may be achieved through crossbreeding previously separated, genetically differentiated cohorts.