Temperature-induced changes in body lipid composition affect vulnerability to oxidative stress in Daphnia magna.

Optimizing physiological functions at different temperatures includes shifts in the lipid composition of ectothermic animals. These shifts may be associated with changes in lipid peroxidation in response to oxidative stress, because lipids differ in their susceptibility to oxidative damage. Polyunsaturated fatty acids (PUFA) are particular prone to peroxidation. Here, we analyzed changes in the fatty acid composition, cholesterol content and the level of oxidative damage as thiobarbituric reactive substances (TBARS) in Daphnia magna as a function of acclimation temperature. The total fatty acid content was highest in cold-acclimated animals. The relative share of most PUFA decreased with increasing acclimation temperature. In contrast, the contribution of saturated and monounsaturated fatty acids (SFA and MUFA) increased with acclimation temperature, although the latter to a lower extent. Cholesterol content remained unchanged. The level of oxidative damage was lowest in animals reared at warm temperatures, most likely reflecting their lowest content of PUFA. Heat exposure (1 h at 33 °C) caused the highest increase in lipid peroxidation in cold-acclimated animals, containing more PUFA. Our data suggest that cold-induced adjustments in the body lipid composition increase the vulnerability of zooplankton to heat-induced oxidative stress. In particular, animals performing diel vertical migration may be highly susceptible to temperature-induced lipid damage.