Predation risk induces stress proteins and reduces antioxidant defense

1 Despite its wide ecological relevance, we know little about the physiological mechanisms underlying the growth vs. mortality by predation trade-off. Here, we test for two costly, potential physiological correlates of the fight-or-flight response that may contribute to the growth reduction under predation risk: induction of stress proteins (Hsp60 and Hsp70) and of antioxidant enzymes (superoxide dismutase, SOD and catalase, CAT), in larvae of the damselfly Enallagma cyathigerum. 2 Under predation risk, there was a growth reduction and an increase in oxygen consumption, indicative of the fight-or-flight response. Predation risk did not affect Hsp60 levels but induced an increase in energetically costly Hsp70 levels. 3 Under predation risk, levels of SOD remained constant and those of CAT decreased. Together with the increase in respiration, this should inevitably result in oxidative stress. 4 Our results suggest that induction of stress proteins may contribute to the partly physiologically mediated growth reduction under predation risk and that oxidative stress is a novel cost of predation risk that may have important long-term negative fitness consequences for the prey. The latter adds to the recent insight that costs of stressors and life-history trade-offs may not always directly operate through increased energy consumption and differential allocation, but, may also work through the increased production of reactive oxygen species.