Resource availability and life-history origin affect competitive behavior in territorial disputes

Partial migration, in which some individuals of a population migrate and others remain sedentary, is a phenomenon that occurs across a wide range of taxa, but the factors that predispose particular individuals to one or the other strategy are usually unknown. Brown trout (Salmo trutta) initially compete for feeding territories in freshwater streams, but while some individuals remain resident in fresh water throughout their lives, others undertake an anadromous migration. Because one of the drivers for migration is the relative rates of resource acquisition in different habitats, we compared the ability of juvenile offspring from freshwater-resident and anadromous parents to compete for feeding territories; we also tested how this depended on the quality of the environment previously experienced. Brown trout derived from freshwater-resident or anadromous parents were reared for ~7 months under high-, mid-, or low-food regimes and were then induced to compete for feeding territories in a seminatural stream channel. We found that the parental type had a significant effect on dominance status in territorial interactions, with offspring of anadromous fish being dominant over size-matched offspring of freshwater residents, but only when both had been raised under intermediate levels of food availability. The results suggest that the migration strategy of the parents interacts with the environmental conditions experienced by the offspring to potentially influence its motivation to compete for feeding territories and hence its probability of migration.