GAMETIC INCOMPATIBILITY IN WILD AND CULTURED POPULATIONS OF THE EASTERN OYSTER, CRASSOSTREA-VIRGINICA (GMELIN)

Fertilization rates were measured in 100 2 X 2 crosses of oysters ( Crassostrea virginica) from six hatchery lines and one natural population. Analysis of fertilization by a log-linear model showed significant interaction between sources of gametes for 30 of the crosses. Gametic compatibility indices (GCI), which estimated the rates of fertilization within populations relative to between-population matings, were more often positive than negative, indicating a slight advantage to within-population matings. However, of the 30 significant cases, GCI was positive in 15 cases and negative in 15 cases. A mass spawning of oysters in which aliquots of pooled eggs were fertilized separately by individual males showed a highly significant sire-dam interaction in yield of juveniles, reflecting differences in larval viability as well as sperm-egg interactions. The existence of moderate gametic incompatibility together with sire-dam interaction effects on larval viability may pose problems in oyster breeding programs employing the mass spawning of small numbers of broodstock.