Flexibility in metabolic rate and activity level determines individual variation in overwinter performance

Area of Science:

• Animal physiology
• Ecology
• Behavioral ecology

Background:

• Overwinter survival relies on energy stores, but depletion rates vary among individuals.
• Physiological and behavioral flexibility in response to food scarcity may explain these differences.
• Understanding how these traits interact is crucial for winter energy use.

Purpose of the Study:

• To investigate individual flexibility in standard metabolic rate (SMR) and activity levels during food scarcity.
• To determine how these flexible traits collectively impact lipid store depletion in overwintering brown trout (Salmo trutta).
• To explore the relationship between changes in metabolism and activity.

Main Methods:

• Simulated winter conditions with food scarcity were imposed on overwintering brown trout.
• Standard metabolic rate and activity levels were measured for each individual.
• Lipid store depletion was quantified over the simulated winter period.

Main Results:

• Metabolism and activity generally decreased under food scarcity, but with significant individual variation.
• Individuals with greater reductions in metabolism and/or activity showed lower lipid depletion rates.
• Changes in metabolism and activity were negatively correlated: reduced SMR often accompanied increased activity, and vice versa.

Conclusions:

• Brown trout exhibit diverse strategies for coping with winter food scarcity.
• Individual flexibility in metabolic rate and activity level influences overwinter energy conservation.
• Negative correlations between metabolic and activity adjustments suggest distinct coping mechanisms among individuals.