Genetic Variation Associated with Alternative Life History Phenotypes in the Atlantic Salmon

A current objective in discovering the capacity to respond to natural selection in wild organisms is to decompose the variation of phenotypic traits into their environmental and heritable components. Thus, one important question is whether phenotypic traits have significant levels of genetic variance, as this determines whether a trait will respond to selection. In addition, the genetic relationships between traits also affect their independent capacity to respond to selection. Therefore, a second question to ask is whether traits share their genetic variance or covary genetically. Alternative reproductive phenotypes in salmonds are characterised by categories of extreme phenotypic variation. The incidence of these categories, and the traits measured within vary substantially. However, little is known about the extent of genetic variation in these traits. This study aims to explore the genetic variance associated with alternative developmental pathways (migratory vs resident males) in Salmo salar, using a common rearing experiment. Genetic variation is found ubiquitously in traits measured across the ontogeny of these phenotypes and in other life-history traits that directly influence their activation. Moreover, the alternative courses of development cause a significant decoupling of the genetic variance of the body mass. Overall, the presence of genetic variance in the measured traits suggests that phenotypic diversity in this species may be generated by the action of natural selection. Such a phenotypic response may occur during larval, juvenile, sexually mature, or migratory stages. The different patterns of genetic covariation within the alternative phenotypes suggest that these life-history pathways may have different capacities to respond to selection. Future studies should aim to investigate the shape and intensity of selection on the measured traits