Abstract
BackgroundGenomic analyses have the potential to impact selective breeding programs by identifying markers that serve as proxies for traits which are expensive or difficult to measure. Also, identifying genes affecting traits of interest enhances our understanding of their underlying biochemical pathways. To this end we conducted genome scans of seven rainbow trout families from a single broodstock population to identify quantitative trait loci (QTL) having an effect on stress response to crowding as measured by plasma cortisol concentration. Our goal was to estimate the number of major genes having large effects on this trait in our broodstock population through the identification of QTL.ResultsA genome scan including 380 microsatellite markers representing 29 chromosomes resulted in the de novo construction of genetic maps which were in good agreement with the NCCCWA genetic map. Unique sets of QTL were detected for two traits which were defined after observing a low correlation between repeated measurements of plasma cortisol concentration in response to stress. A highly significant QTL was detected in three independent analyses on Omy16, many additional suggestive and significant QTL were also identified. With linkage-based methods of QTL analysis such as half-sib regression interval mapping and a variance component method, we determined that the significant and suggestive QTL explain about 40-43% and 13-27% of the phenotypic trait variation, respectively.ConclusionsThe cortisol response to crowding stress is a complex trait controlled in a sub-sample of our broodstock population by multiple QTL on at least 8 chromosomes. These QTL are largely different from others previously identified for a similar trait, documenting that population specific genetic variants independently affect cortisol response in ways that may result in different impacts on growth. Also, mapping QTL for multiple traits associated with stress response detected trait specific QTL which indicate the significance of the first plasma cortisol measurement in defining the trait. Fine mapping these QTL can lead towards the identification of genes affecting stress response and may influence approaches to selection for this economically important stress response trait.
Highlights
Genomic analyses have the potential to impact selective breeding programs by identifying markers that serve as proxies for traits which are expensive or difficult to measure
We report the detection of multiple quantitative trait loci (QTL) for stress response as defined by Pottinger and Carrick [18] and modified by Weber and Silverstein [12] in a mapping population sampled from broodstock under selection for growth
Suggestive and significant QTL affecting stress responses were detected on eight chromosomes in a survey of seven families from a single broodstock population
Summary
Genomic analyses have the potential to impact selective breeding programs by identifying markers that serve as proxies for traits which are expensive or difficult to measure. Typical stressors can be categorized under handling and manipulation, overcrowding, suboptimal water quality parameters, and social interactions, all of which have been shown to negatively affect production traits such as growth, feed intake, feed efficiency, disease resistance, flesh quality, and reproductive performance [2,3,4,5,6,7] Fish respond to these stressors in similar patterns to those exhibited by terrestrial vertebrates, by stimulating the hypothalamic-sympatheticchromaffin cell axis which releases catecholamines to increase oxygen uptake and energy mobilization and the hypothalamic-pituitary-interrenal axis, which produces cortisol to effect carbohydrate, protein, and lipid metabolism [8]. An appropriate hormonal response enables the fish to endure a stress; excessive or prolonged exposure to these hormones, cortisol, can have deleterious effects on traits associated with aquaculture production [3]
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