Phenotypic Correlation of Juvenile Growth Rate between Different Consecutive foraging Environments in a Salmonid fish: A Field Experiment

Many organisms occupy considerably different environments during individual's lifespan. We are interested in how the phenotypic characteristics that are favourable in the earlier environment predict fitness in the later environment. High predictability of fitness between the two consecutive environments suggests that the either the same traits are favored in both environments, or that the favourable traits are genetically correlated. In this study, we ask how similarity of consecutive foraging environments affects the phenotypic correlation of juvenile brown trout growth rate. More specifically, we used a genetically narrow stock of hatchery-bred fish to contrast individual growth rates between high and low density hatchery environments, and thereafter between hatchery and natural lake environment. As expected, growth rate was highly dependent on the environment, and the fish showed considerable phenotypic plasticity. Furthermore, we found a strong positive correlation in growth rate between similar foraging environments, for example, between high and low density hatchery stocks, and between hatchery and a lake with small fish as main prey. However, hatchery growth did not predict growth rate in lakes where fish had to forage on bottom-dwelling invertebrates. Our results suggest that when the consecutive environments differed dramatically with respect to traits that fish use for foraging, relative performance of individual fish changed, earlier performance not being an accurate predictor of performance in the new environment. In this case, fitness of the fish was determined by an environment-specific set of traits that were not the same between the two consecutive environments. The result indicates that assessment of individual performance may be highly environment specific in trout. This revised version was published online in July 2006 with corrections to the Cover Date.