Genetic parameters for tolerance to a controlled heat stress challenge in northern Gulf of America eastern oyster, Crassostrea virginica

Excessively high temperatures in the Gulf of America are one of the major drivers of summer mortalities of eastern oysters. In this study, the feasibility of improving tolerance to extreme high temperature by selection was evaluated in common garden experiments employing a mixture of 80 half-sib and 160 full-sib families. Heat stress tolerance was evaluated in controlled challenges applying a sustained temperature of 38–39 °C to juveniles (3.5 months) and adults (14 months) until complete mortality (>99% mortality rate) was reached. Survival duration of individual oysters during challenges was recorded and parentage was inferred using genotypes at 192 Single Nucleotide Polymorphism markers. Heritability of heat-stress tolerance in juveniles estimated using animal mixed-models was non-significant (0.216 ± 0.199) but the non-additive genetic variance component differed significantly from zero (0.397 ± 0.170). Heritability of heat-stress tolerance in adults was high (0.749 ± 0.086) and the non-additive component of genetic variance was insignificant at that stage. The genetic correlations between juvenile and adult tolerance was intermediate (0.672 ± 0.205) indicating that the juvenile challenge was of moderate value to predict breeding values for adult tolerance. The estimate of genetic correlation between adult tolerance and shell height did not differ significantly from zero (0.056 ± 0.181), suggesting that selection to improve growth rate in height would not affect heat-stress tolerance as measured in this challenge. Genetic correlation between heat-stress tolerance and the hinge backbend shell abnormality severity score was negative (−0.377 ± 0.139), indicating that reduction of the backbend incidence could contribute to improved heat-stress tolerance.