Breaking Free from Thermodynamic Constraints: Thermal Acclimation and Metabolic Compensation in a freshwater zooplankton species

Ectothermic organisms' respiration rates are largely controlled by environment temperatures and the ability to meet metabolic demands at high temperatures sometimes sets their upper thermal limit. Organisms are hypothesized to exhibit acclimatory effects, adjusting their metabolism and physiology by deceleration of metabolic processes including respiration below Arrhenius expectations based in temperature alone. Such deceleration is termed metabolic compensation. We test the hypothesis that either heritable (among genotypes) or plastic (between acclimation regimes) heat tolerance differences can be explained by metabolic compensation in the eurythermal freshwater zooplankton crustacean Daphnia magna. We measured oxygen consumption rates over a range of assay temperatures (5°C - 37°C) in 8 genotypes of Daphnia representing a range of previously reported genotype-specific acute heat tolerance values and, in a narrower range of temperatures (10°C - 35°C) in Daphnia with different acclimati...