The genomics of growth and blue spots in a cultured population of Australasian snapper Chrysophrys auratus
Authors:   , Ashton David T. 
Published: December 2021

<p>Characterizing the genome and understanding how it influences phenotypic variation is a central goal for studies on evolution. The findings of genomic research are applicable to a wide range of human endeavours, including predicting disease risk, supporting selective breeding programmes, and understanding adaptive variation in natural populations. One industry that could particularly benefit from this knowledge is Aquaculture. In recent years, aquaculture production has been increasing to offset the production limits of wild fisheries. Genomics can be used in aquaculture to quantify variation of captive populations, reconstruct pedigrees, and improve the gains from selective breeding programs. The overall goal of this thesis research was to generate a genome-wide genotyping dataset and investigated several key traits for Australasian snapper (Chrysophrys auratus or Pagrus auratus). The findings will be used to establish one of the first genomics-informed New Zealand aquaculture programmes and provide a better understanding of the genotype-phenotype relationships in this teleost species.  The first two chapters of this thesis provide a review of the literature and establish the background information and context for the research in subsequent data chapters. A brief overview of genomics, fisheries and aquaculture, and the intersection of these two fields are provided in the Chapter 1. An in-depth quantitative review of 146 Quantitative Trait Loci (QTL) studies in teleost fish was then carried out in Chapter 2.  Chapter 3 provides details about the study population and the collection of genotyping data. Genotyping-By-Sequencing (GBS) was used to generate 11K Single Nucleotide Polymorphism (SNP) markers for individuals in the three generation pedigree. Together with phenotypic data the genotyping was used to reconstruct the pedigree, measure inbreeding, and estimate heritability for a range of traits. Parents were identified for 93% of the offspring and successful pedigree reconstruction indicated highly uneven contributions of each parent to the subsequent generations. The average inbreeding level did not change between generations, but significantly different inbreeding levels were observed between offspring from the two founding cohorts and as a result full and half sibling crosses within the group spawning teleost species. Heritability was estimated for a range of traits using both a pedigree relatedness matrix and a genomic relatedness matrix.  Chapter 4, uses the genotyping and phenotyping data to generate a linkage map and carry out a scan for quantitative trait loci (QTLs) associated with growth rate. The linkage map reported in this thesis is one of the highest density maps for any Sparidae species at the time of writing. It contained 24 linkage groups, which represent the 24 snapper chromosomes. Growth QTLs were found on three linkage groups and a scan of available genome data identified three candidate growth genes nearby on the linkage groups.  Chapter 5, uses the genotyping data and images collected during the study to characterize snappers blue spots and search for QTLs associated with spot numbers. QTLs were found on 12 of the 24 linkage groups, of which one was consistent between two QTL methods applied. A scan of available genome data identified the tyrosinase gene in the middle of the putative QTL region, which is a causal gene for iridophore cell numbers that form blue spots in other fish species.  Chapter 6, discuss the implications, future directions, and application of this research to the snapper breeding programme.</p>