Diet drives performance trade-offs along the ontogeny in the Atlantic salmon

Abstract

Understanding the mechanistic basis of life history divergence is fundamental for predictive ecology. Variation in resource use impacts life history divergence and provides a framework for studying life history trade-offs. Contrary to the theory, empirical evidence does not support that resource allocation alone mediates life history divergence in the wild, which subsequently suggests a pivotal role for resource acquisition, but this has not been empirically demonstrated in free-living populations. Here, we sampled wild Atlantic salmon (Salmo salar) from different age groups during their marine feeding stage and hypothesized that prey taxa (crustaceans versus fish) have an age-dependent effect on the condition factor. We found that salmon in their first year at sea had a higher condition factor when foraging on larger numbers of crustaceans and a lower condition factor when foraging on larger numbers of fish, and vice versa in older sea age groups. Provided that condition factor is a predictor of age-at-maturity, our results show that resource acquisition may be an important process shaping life history variation in Atlantic salmon via modulating age-dependent performance trade-offs. Our results also emphasize the importance of bottom-up trophic cascades for maturation age and help to better predict the maturation dynamics of wild populations in the marine environment.