The presence of the Pacific Oyster OSHV-1 resistance marker on chromosome 8 does not impact susceptibility to infection by Vibrioaestuarianus

Abstract

The Pacific oyster, Crassostrea gigas, is an important species in global aquaculture, but its production is threatened by pathogenic infections such as Ostreid herpesvirus 1 (OsHV-1) and Vibrio aestuarianus. A genetic marker for OsHV-1 resistance has been identified on chromosome 8 of the Pacific oyster genome, and selective breeding has been performed to produce OsHV-1-resistant oysters. However, the potential impact of this marker on susceptibility to other pathogens remains unknown. In this study, we assess the effect of the presence and allelic dosage of the OsHV-1 resistance marker on susceptibility to V. aestuarianus infections in selectively bred oyster families from the Molluscan Broodstock Program of Oregon State University. Sixteen families were produced with various states of the OsHV-1 resistance marker, and a disease challenge with V. aestuarianus was performed on these families to track mortality in each individual. Challenged oysters were genotyped at the OsHV-1 resistance locus, and Vibrio susceptibility was compared among genotype groups within and between families. Additionally, double digest reduced representation sequencing (ddRADseq) was performed on challenged oysters, and a genome-wide association study was conducted for survivorship from the Vibrio exposure. Results showed that prior to the Vibrio exposure, the OsHV-1 resistance marker was not observed at the expected Mendelian inheritance ratios in families, with a significantly reduced presence of the homozygous alternate genotype in 75% of heterozygote family crosses. Among the 16 families, mortality rates differed significantly following exposure to V. aestuarianus (range: 85.4% to 47.9%), but there was no association found between the chromosome 8 marker and survival to Vibrio infection. No loci were found to be significantly associated to survivorship to Vibrio infection, suggesting Vibrio resistance in these families is not controlled by one or a few loci of large effect.