The effect of food availability on thermal stress inDaphnia magna: trade-offs among oxidative stress, somatic growth, and reproduction

Abstract

The effects of food availability on thermal stress inDaphnia magnawere investigated for 21 days, with a hypothesis that lower food condition would increase the adverse effect of elevated temperature onD. magna. Under higher food conditions (5 x 10(5) cells mL(-1)), elevated temperature (25 degrees C) did not induce higher oxidative stress (levels of antioxidant enzymes and lipid peroxidation) than reference temperature (20 degrees C). Thus, reproduction (number of offspring per female) was significantly (p < 0.05) higher at 25 degrees C compared with that at 20 degrees C. Under lower food condition (2 x 10(5) cells mL(-1)), however, elevated temperature significantly (p < 0.05) induced antioxidant enzyme activity (superoxide dismutase and catalase) and reduced adult somatic growth rate (5-21 days), whereas there was no significant change in reproduction between the two temperature groups. These findings suggest that food availability greatly influences the effect of elevated temperature onD. magna, possibly resulting in a trade-off among oxidative stress defense, somatic growth, and reproduction.