Graduate Thesis Or Dissertation
 

Quantitative and molecular genetics of larval susceptibility to Vibrio tubiashii in Pacific oysters (Crassostrea gigas)

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6108vd72d

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  • Vibriosis caused by the bacterial pathogen Vibrio tubiashii is one of several factors contributing to mass larval mortalities of the Pacific oyster (Crassostrea gigas) in Pacific Northwest shellfish hatcheries in recent years. Genetically improved strains of the Pacific oyster resistant to V. tubiashii would be highly desirable. This study investigates quantitative and molecular genetics of resistance to V. tubiashii in Pacific oyster larvae that could be used for marker-assisted selection. In experiment 1, we measured the survival of larvae samples from 30 full-sib families under V. tubiashii-free conditions and when exposed to 3 different concentrations of V. tubiashii. We found that heritability of survival was surprisingly high but also variable, depending upon V. tubiashii concentration. We also found strong genotype by environment interactions, meaning families responded differently to changes in the environments. In experiment 2, we scanned the oyster genome for single nucleotide polymorphisms (SNP) associated with V. tubiashii resistance by comparing allele frequencies between two larvae pools: survivors of a laboratory V. tubiashii challenge and contemporary unchallenged controls in each of four full-sib families. In total, we identified 262 SNPs with significantly different allele frequencies between the survivors and the contemporary controls. In experiment 3, we used a tag-base RNA-Seq procedure to quantify transcriptomes of 3 samples for each family: larvae taken at the beginning of the experiment (0-hour control), larvae raised for 12 hours without V. tubiashii (12-hour control), and larvae raised for 12 hours with V. tubiashii (12-hour treatment). We identified 12 differentially expressed genes between resistant and sensitive families. In addition, we confirmed the observation of Taris et al. (2009) that transcriptional differences between resistant and sensitive families exists prior to a bacterial challenge, supporting the hypothesis that difference in resistance to V. tubiashii is due to inherit differences in gene expression rather than differential responses to pathogen challenge. These experiments provide both insight into the biology of larval resistant to V. tubiashii in Pacific oyster, and candidate genes and molecular markers that can be used for marker-assisted selection to develop genetically improved oyster strains resistant to V. tubiashii.
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