Genetic effects on Atlantic salmon (Salmo salar) survivorship
Abstract
The major histocompatibility complex (MHC) is a large multi-gene family that plays a fundamental role in regulating the vertebrate immune response. These genes are highly polymorphic, and their diversity is thought to be maintained by (1) natural selection, usually against homozygotes; (2) sexual selection via disassortative mating; or (3) some combination of the two. In this dissertation Atlantic salmon are used to quantify the influence of MHC on survivorship and fitness of Atlantic salmon. I begin by looking at the effects of MHC and genome-wide relatedness on early offspring mortality, and find there is no significant relationship between genetics and survivorship. I then look for evidence of contemporary natural selection by looking for a relationship between MHC and genome-wide diversity on survivorship and lifetime fitness as measured by the number of offspring returning to breed. I find that female internal relatedness (IR) and parental relatedness are negatively correlated with fitness, but there are no MHC effects. Subsequently, I attempt to link the genetic measures analyzed herein with physical and fitness characteristics and find a strong relationship between female body size and the number of eggs produced but weaker relationships between other genetic, physical and fitness traits. Finally, I look for a relationship between MHC zygosity and Renibacterium salmoninarum, the causal agent of bacterial kidney disease and find that MHC heterozygotes are less susceptible to R. salmoninarum than are homozygotes. Taken together, these results suggest that factors other than MHC (e.g. IR or body size) may play a more important role in overall fitness of Atlantic salmon. This may be due to weak selection on fish from the hatchery environment, or that the contemporary signature of natural selection is difficult to detect in the current generation. While MHC genotype is related to resistance of specific pathogens, the combined influence of the entire community of pathogens encountered in nature may obscure the imprint of natural selection on wild populations.
Degree
Ph.D.
Advisors
DeWoody, Purdue University.
Subject Area
Genetics
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