Genetic growth potential, rather than phenotypic size, predicts migration phenotype in Atlantic salmon

Abstract

Knowledge of the relative importance of genetic versus environmental determinants of major developmental transitions is pertinent to understanding phenotypic evolution. In salmonid fishes, a major developmental transition enables a risky seaward migration that provides access to feed resources. In Atlantic salmon, initiation of the migrant phenotype, and thus age of migrants, is presumably controlled via thresholds of a quantitative liability, approximated by body size expressed long before the migration. However, how well size approximates liability, both genetically and environmentally, remains uncertain. We studied 32 Atlantic salmon families in two temperatures and feeding regimes (fully fed, temporarily restricted) to completion of migration status at age 1 year. We detected a lower migrant probability in the cold (0.42) than the warm environment (0.76), but no effects of male maturation status or feed restriction. By contrast, body length in late summer predicted migrant probability and its control reduced migrant probability heritability by 50–70%. Furthermore, migrant probability and length showed high heritabilities and between-environment genetic correlations, and were phenotypically highly correlated with stronger genetic than environmental contributions. Altogether, quantitative estimates for the genetic and environmental effects predicting the migrant phenotype indicate, for a given temperature, a larger importance of genetic than environmental size effects.

Sex-specific lipid profiles in the muscle of Atlantic salmon juveniles

“…The upper modal group are more likely to smolt and migrate to the sea the following spring while the lower modal group are more likely to remain in freshwater for at least an additional year (Thorpe 1977, Bailey et al, 1980, Kristinsson et al, 1985). An earlier study showed that body length during the late summer and fall was able to predict the probability of a spring migration the following year and that both traits are genetically highly correlated (Debes et al, 2020a;). However, some individuals in the lower modal group can still grow rapidly during the winter and become migrants in the following spring (Debes et al, 2020a; Zydlewski et al, 2014).…”

“…A recent study found that body length during the late summer was able to predict the probability of a spring migration the following year while its control reduced migrant probability heritability by up to 70% (Debes et al, 2020a). However, some individuals in the lower modal group can still grow rapidly during the winter and become migrants in the following spring (Debes et al, 2020a; Zydlewski et al, 2014).…”

Maturation in Atlantic salmon (Salmo salar, Salmonidae): a synthesis of ecological, genetic, and molecular processes

“…A recent common garden study that partitioned genetic and environmental effects found that environmental factors such as water temperature were important for smoltification. However, for a given temperature, genetic factors were more important than environmental effects in predicting smoltification probability (Debes et al 2020).…”

“…This lowered probability of survival is also likely a result of investment into reproduction. However, a number of experimental studies have not found an association with male parr maturation and the probability of smolting (Debes et al 2020;Duston and Saunders 1997) suggesting that these two processes may be decoupled.…”

“…Progress to date is thanks, in large part, to the ability to monitor maturation of the same individuals at different points in their life-history. For example, longitudinal studies using traditional approaches including common garden studies (Debes et al 2020;O'Toole et al 2015;Skaala et al 2019), tagging (Chaput et al 2018;Thorpe et al 1981), inferring life history strategies via scale readings (e.g., Erkinaro et al 2019;Mobley et al 2020), or a combination of several of these (Norrgård et al 2014) have illuminated patterns of maturation in a variety of ecologically relevant settings.…”