Quantitative trait locus analysis of hatch timing, weight, length and growth rate in coho salmon, Oncorhynchus kisutch.

In quantitative genetics, multivariate statistical approaches are increasingly used to describe genetic correlations in natural populations, yet the exact genetic relationship between phenotype and genotype is often unknown. Quantitative trait locus (QTL) analyses can be used to describe the molecular basis of this relationship. In salmonids, growth and development are important fitness traits that are phenotypically correlated with each other and with other life-history traits, and an understanding of the molecular basis of these relationships is valuable for future evolutionary studies. Here, a QTL analysis using an outbred cross was initiated to determine the molecular basis of phenotypic correlations between such growth traits in coho salmon (Oncorhynchus kisutch), an important fish species distributed throughout the North Pacific Ocean. Fifty-three QTL for growth rate, length and weight at eight time periods were located on seven linkage groups (OKI03, OKI06, OKI18, OKI19, OKI23, OKI24 and an unnamed linkage group) or associated with five unlinked markers (Omm1159, Omm1367/i, Omy325UoG, OmyRGT55TUF and OtsG422UCD). One QTL for hatch timing was associated with the marker, Omm1241. All QTL were of minor effect, explaining no more than 20% of the observed variation in phenotypic value. Several instances of colocalization of QTL weight, length and growth rate were observed, suggesting a genetic basis for phenotypic correlations observed between these traits. This study lays the foundation for future QTL mapping efforts, for detailed examinations of the genetic basis of phenotypic correlations between growth traits, and for exploring the adaptive significance of growth traits in natural populations.