DOI: 10.5061/dryad.c2fqz616k
title: Breaking Free from Thermodynamic Constraints: Thermal Acclimation and Metabolic Compensation in a freshwater zooplankton species

description: 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.
description: 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: 
 run run ID assayT Temperature at which O2 consumption measurement was conducted Slope_mg/sec blank-corrected slope of [O2] over time SE(Slope_mg/sec) its SE SlopeUA_mg/sec blank-corrected slope of [O2] over time in urethane-anaesthetizes Daphnia SE(SlopeUA_mg/sec) its SE N Number of Daphnia in assay wweight(mg) Combined wet weight of Daphnia in assay Clone clone ID AccT  Acclimation temperature Treatment: Recovery treatment OR time at new T Treatment in the recovery experiment or time (h) at the new temperature in acclimation reversal experiment ugO2/min/mgWW oxygen consumed per minute per mg of wet weight ugO2/min/Daphnia oxygen consumed per minute per individual Daphnia ugO2UA/min/mgWW oxygen consumed per minute per mg of wet weight in urethane-anaesthetizes Daphnia ugO2UA/min/Daphnia oxygen consumed per minute per individual Daphnia in urethane-anaesthetizes Daphnia