Foraging and thermally induced phenotypic plasticity interact in the most northerly distributed freshwater fish.

Elevated temperatures from climate change are predicted to be more extreme at higher latitudes. This could require phenotypic plasticity to generate variation that allows organisms to persist in these regions. However, climate change will provide a multifactorial change in environmental cues, making an understanding of how they interact essential for predicting persistence and future evolutionary potential. Here, the impacts of temperature on ecologically relevant phenotypic plasticity (foraging environment) in Arctic charr () were studied. Eggs and alevins were kept at the same temperature (9°C) and split using a factorial design. This included two temperature treatments (10°C and 14°C) and two treatments representing benthic and pelagic foraging styles. We measured morphology in response to these treatment combinations and found an interaction between foraging and temperature-induced plasticity in body shape that included changes in body depth and the caudal peduncle that could impact swimming ability and fitness. This indicates that thermal conditions may change how plasticity responds to ecological conditions and impact adaptive variation.