Plasticity and Trade-Offs in the Growth of Migratory Brown Trout (Salmo trutta)

Many species tend to migrate within relatively narrow time windows despite the fact that individual variation in fitness traits likely to affect migration performance, for example in body size or in fat reserves, may differ substantially. Given that timing of migration has a strong genetic component (Hansen et. al 1991), a trade-off may exist between moving when it is best for the group and when it is best for the individual. Inevitably, some individuals will travel at suboptimal times, thereby constraining the expression of adaptive phenotypic plasticity. Here we used measurements of scale inter-circuli spacing and marine growth (post-smolt growth, PSG) to reconstruct individual variation in growth profiles of migratory brown trout  (Salmo trutta) inhabiting six neighbouring rivers.