Costs of immunity in insects: an induced immune response increases metabolic rate and decreases antimicrobial activity

Abstract

Summary 1. Life-history theory predicts that immune responses have evolved in the context of costs and benefits. However, our understanding of the costs of mounting an immune response is limited. 2. Using four species of insects, we tested for metabolic costs of immunity by inducing a short-term immune response and/or wounding and measuring CO2 production. Inducing an encapsulation response and/or wounding raised resting metabolic rate by up to 28% with a strong positive correlation between individual encapsulation response and metabolic rate in Tenebrio molitor, Acheta domesticus, Cotinis nitida and Periplaneta americana. Interestingly, we found that haemolymph removal increased metabolic activity relative to only wounding, suggesting a cost to sampling haemolymph. 3. We also tested for how mounting an encapsulation response and/or wounding would affect other immune components. We found that inducing an encapsulation response led to increased levels of phenoloxidase and decreased levels of lysozyme, an antimicrobial protein. 4. Our results support the growing evidence that immune responses entail specific energetic and corresponding physiological costs.