Selection for a single nucleotide polymorphism on chromosome 8 of the genome of Crassostrea gigas improves resistance to both ostreid herpesvirus 1 and Vibrio coralliilyticus

Selection for a single nucleotide polymorphism (SNP) on chromosome 8 improved the survival of oyster spat in Tomales Bay, California, where ostreid herpesvirus 1 (OsHV-1) is endemic. To evaluate whether this improved survival was due to increased resistance to OsHV-1 and to determine whether selection for this SNP affects the resistance of larvae and spat to other pathogens, 12 crosses of C. gigas were produced with offspring that were either heterozygous for the SNP or homozygous for the reference allele (control families). Larvae were challenged with Vibrio coralliilyticus RE22 and OsHV-1 (Tomales variant). Larvae that were heterozygous for the putatively protective allele showed a 5.4 % increase in average survival compared to control families challenged with RE22 but no difference in survival against OsHV-1. Spat were challenged with RE22 and OsHV-1 (United Kingdom μvar). Spat that were heterozygous for the SNP showed a 28.1 % increase in average survival against RE22, and 38.9 % greater survival against OsHV-1. Degree of inbreeding was negatively associated with survival in both spat laboratory challenges. Spat were also planted in Tomales Bay, and the growth, survival, and prevalence of OsHV-1 infection in the planted oysters were assessed. Outplanted oysters that were heterozygous for the SNP had a 10.4 % increase in average survival than control families, lower prevalence of infection with OsHV-1, and lower viral loads in infected oysters. Additional spat were planted in Willapa Bay, Washington, and survival and growth were equivalent between families of the two genotypes. Across all families, survival in Tomales Bay was significantly correlated with survival after spat laboratory challenges with V. coralliilyticus ( r = 0.60) and OsHV-1 ( r = 0.59). These results confirm that the heterozygous genotype confers resistance of spat to OsHV-1 in laboratory and field trials and to a bacterial pathogen of oysters. • Spat with the ref./alt SNP had higher survival against V. coralliilyticus and OsHV-1. • Spat with the ref./alt SNP had higher survival in Tomales Bay and reduced infection. • Oysters with the ref./alt SNP had equivalent survival and growth in Willapa Bay. • Survival against pathogens in the laboratory and in Tomales Bay was correlated.