Genetic variation affecting fitness in the Eastern oyster (Crassostrea Virginica)
Creators: name: Wang, Zhenwei
Publisher: name: No Publisher Supplied
Year: 2024

description: Genetic variation or genetic diversity plays a crucial role in the adaptability and survival of oyster populations. Comprehending its influence on oyster fitness helps us understand oyster adaptability and contributes to genetic improvement of oysters for aquaculture. This dissertation, comprised of five chapters, delves into the significance and practical applications of genetic variation in the context of oyster fitness and adaptability.Based on the foundation of genetic variation's crucial role in oyster adaptability and survival, this dissertation explores the phenomenon of heterosis and its implications for genetic diversity within oyster populations. Chapter 1 delves into the performance of inbred and hybrid oysters from the D larvae to adult stage, providing concrete evidence of heterosis in terms of oyster survival and growth. The utilization of the recently developed high density single nucleotide polymorphism (SNP) array provides insight into the importance of heterosis and genetic diversity in enhancing oyster performance including survival and growth, contributing to our understanding of heterosis in oysters. Chapter 2 addresses genetic load in the eastern oyster by analyzing genetic markers showing segregation distortion (SD) during the larval stage. This analysis reveals why oysters are sensitive to inbreeding and suffer from inbreeding depression. The high proportion of markers with SD suggests that balancing selection is the main contributing factor to the genetic load and genetic diversity. Furthermore, the discovery of high levels of null alleles in the eastern oyster genome offers insights into other forms of genetic variation in oysters. In Chapter 3, the focus shifts to understanding genetic mechanisms of growth and heterosis through transcriptome analysis. Through gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, distinctions in growth-related physiological strategies among different size groups are illuminated. The identification of candidate genes associated with shell formation and stress response suggest a relationship with growth. Comparing hybrid and inbred transcriptome data suggests hybrids have a more sophisticated regulatory network for optimized stress response. This chapter argues that the observed heterosis in oyster growth results from a combination of additive and non-additive genetic effects. Chapter 4 identifies candidate loci and genes associated with field survival by studying the genetic changes after field mortalities. The findings suggest that field survival is a polygenic trait influenced by many genes related to disease resistance, growth, and thermal tolerance. This study provides a rich source of genetic data for possible genetic improvement of oysters. Finally, Chapter 5 conducts genomic selection (GS) to improve dermo resistance by using genome-wide genotype data. The performance of the F1 generation proves the effectiveness of GS in improving dermo resistance. And it is the first report on the successful application of high-density SNP array and GS in improving dermo resistance in the eastern oyster. In conclusion, this dissertation provides a comprehensive examination of the critical role of genetic variation in the adaptability and survival of eastern oysters. Through detailed investigations spanning from inbred and hybrid performance analyses to high genetic load assessments, to the exploration of genetic mechanisms underlying growth and heterosis, this research highlights the significance of maintaining and promoting genetic diversity within oyster populations. The utilization of high-density SNP arrays and transcriptome data has not only shed light on the phenomenon of heterosis but also contributed to genetic improvement practices in oyster aquaculture. By identifying candidate loci and genes associated with key traits such as field survival and growth, this study provides valuable insights into genetic architecture of production traits, potentially useful for the genetic improvement of oysters. This research demonstrates that GS is effective for improving polygenic traits such as dermo resistance. These findings emphasize that genetic variation is crucial for the adaptability of oysters, and understanding this diversity is critical for oyster aquaculture, breeding and conservation.