The eastern oyster (Crassostrea virginica) is a species that holds strong ecological and economic importance. Dermo disease, caused by the protozoan parasite Perkinsus marinus, is a prominent cause of mortality in the eastern oyster, and is predicted to increase in prevalence with climate change. Thus, there is interest in using genomic and phenotypic selection to increase growth and resilience to dermo in oysters produced for restoration efforts. However, selection for some traits may result in unintentional selection for adverse traits. To that end, the purpose of this study was to determine if selection for growth and dermo resilience impacts thermal tolerance in the eastern oyster.
The oyster lines used in this study included: 1) an unselected wild control, FLWC; 2) a genomic control mated from oysters with average genomic estimated breeding values (GEBVs) for dermo resilience and whole oyster weight, FLC; 3) phenotypically selected oysters based on survival from dermo challenge in laboratory, FLP; and 4) genomically selected oysters based on high GEBVs for dermo resilience and whole oyster weight, FLGS. A chronic LT50 (lethal time that causes 50% mortality rate) assay was conducted, with each line of oysters exposed to 23°C, 28°C, 36°C, and 38°C for 20 days. For each temperature, three replicate recirculating aquaculture systems held 50 animals from each line.
Mortality exceeded 50% only in the 38°C trial. Preliminary analysis shows that the LT50 of the FLP and FLGS groups were significantly higher than that of the FLWC group (Figure 1). Additionally, the LT50 of the FLGS group was significantly higher than the FLC group. Selection for dermo tolerance did not have an adverse effect on thermal tolerance. Rather, genomic and phenotypic selection for resistance to dermo disease significantly increased thermal tolerance when compared to a wild control, and genomic selection significantly increased thermal tolerance in comparison to a genomic control.