High oxidative stress despite low energy metabolism and vice versa: Insights through temperature acclimation in an ectotherm.

Reactive oxygen species (ROS) are inescapable byproducts of energy metabolism and may cause costly damage to biomolecules. Organisms have evolved different means to counter oxidative stress, such as modulation of ROS production, neutralization of produced ROS through free radical scavenging and the repair or removal of the damaged structures. A positive relationship between metabolic rate and ROS production is commonly expected, but the oxidative burden of aerobic metabolism remains poorly understood. We investigated whether acclimation to ambient temperatures imposing variation in standard metabolic rate (SMR) is mirrored in the oxidative status of an ectotherm. Grass snakes (Natrix natrix) acclimated for six months to warm (32 °C) conditions revealed seven times higher SMR compared to cold-acclimated (18 °C) individuals. In contrast to SMR, the amount of damage measured as reactive oxygen metabolites test (dROMs) and abundance of micronucleated erythrocytes was significantly lower in warm-acclimated individuals, while non-enzymatic antioxidant capacity of plasma was unaltered by thermal acclimation. Our results support that high SMR may allow snakes to better cope with oxidative stress, possibly through tissue repair or removal of damaged tissues that also requires energy costs. The reversed association between self-maintenance metabolism and oxidative damage to biomolecules provides novel rational for temperature dependent life histories of ectotherms. How oxidative stress may contribute to the known reduced rates of ectotherm growth or reproduction under cold temperatures or if oxidative stress may even drive such life history trait declines are now important challenges to be addressed.