Mapping of quantitative trait loci for temporal growth and age at maturity in coho salmon: Evidence for genotype-by-sex interactions

Phenotypic differences between males and females are ubiquitous throughout the animal kingdom. Therefore, investigating the extent to which sex-dependent genetic effects contribute to phenotypic variation is important in understanding the evolutionary response of each sex to natural and artificial selection. Sex-specific differences in growth patterns and age at sexual maturity have been observed in a number of anadromous salmonid fishes. In these species, faster growing individuals in a given cohort often mature earlier than conspecifics, and earlier maturing individuals are often males. The aim of this study was to determine whether sex-dependent genetic effects contribute to phenotypic variation in age at sexual maturity and growth in coho salmon reared through juvenile stages to first maturity. To achieve this aim, quantitative trait loci (QTL) underlying growth-related traits and age at first maturity were mapped across four families, and interactions between offspring sex and trait were examined by investigating the significance of genotype-by-sex (QTL x sex) interactions. Several temporally expressed growth-related QTL mapped to the same position, suggesting that these regions affected growth across many months. QTL x sex interactions were widespread, indicating that the effect of QTL on age at sexual maturity and growth over the course of development in coho salmon may be under sex-specific genetic control. We also found evidence for epistatic interactions between some growth traits. Our results provide insights into the genetic architecture underlying growth-related traits in coho salmon, and have implications for understanding the genetic and evolutionary basis of important fitness-related traits.