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 acclimation history (either 10°C or 25°C). In a ramp-up experiment we discovered no difference in temperature-specific respiration rates between heat tolerant and heat-sensitive genotypes. In contrast, we observed compensatory differences in respiration rates at both extremes of the temperature range studied. Notably, there was a deceleration of oxygen consumption at higher temperature in the 25°C-acclimated Daphnia relative to their 10°C-acclimated counterparts, observed in active, but not anaesthetized animals, a pattern corroborated by similar changes in filtering rate and, partly, by changes in mitochondrial membrane potential. Daphnia exposed to a sublethal temperature (35°C) with a 24-hour recovery period at a 25°C-acclimation temperature showed no difference in respiration compared to unexposed 25°C-acclimated Daphnia, indicating that the reduction of respiration is not caused by irreversible damage. Response time necessary to acquire the respiratory adjustment to high temperature was much lower than to low temperature, indicating that metabolic compensation at the lower temperatures require slower structural changes.

Data are available for the following experiments: respiration rates in a Ramp-UP temperature; respiration rates in thermal Acclimation experiments 1 and 2; respiration rates in the Recovery experiment; respiration rates in the Acclimation Reversal time experiment; mitochondrial membrane potential in the Acclimation experiment.

Missing values: In Acclimation experiments 2 both active and basal respiration was measured in some animals, but only either one or the other in others. 

Data consist of the following data columns: