Department of Biological Sciences, East Tennessee State University, Johnson City, TN 37691, USA.
Department of Biological Sciences, University of Notre Dame, Galvin Life Science Center, Notre Dame, IN 46556, USA.
J Exp Biol. 2021 Feb 19;224(Pt 4):jeb237727. doi: 10.1242/jeb.237727.
Respiration rates of ectothermic organisms are affected by environmental temperatures, and sustainable metabolism at high temperatures sometimes limits heat tolerance. Organisms are hypothesized to exhibit acclimatory metabolic compensation effects, decelerating their metabolic processes below Arrhenius expectations based on temperature alone. We tested the hypothesis that either heritable or plastic heat tolerance differences can be explained by metabolic compensation in the eurythermal freshwater zooplankton crustacean We measured respiration rates in a ramp-up experiment over a range of assay temperatures (5-37°C) in eight genotypes of representing a range of previously reported acute heat tolerances and, at a narrower range of temperatures (10-35°C), in with different acclimation history (either 10 or 25°C). We discovered no difference in temperature-specific respiration rates between heat-tolerant and heat-sensitive genotypes. In contrast, we observed acclimation-specific 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 25°C-acclimated relative to their 10°C-acclimated counterparts, observed in active animals, a pattern corroborated by similar changes in filtering rate and, partly, by changes in mitochondrial membrane potential. A recovery experiment indicated that the reduction of respiration was not caused by irreversible damage during exposure to a sublethal temperature. Response time necessary to acquire the respiratory adjustment to high temperature was lower than for low temperature, indicating that metabolic compensation at lower temperatures requires slower, possibly structural changes.
变温动物的呼吸速率受环境温度的影响，而在高温下可持续的新陈代谢有时会限制其耐热性。人们假设生物体表现出适应性代谢补偿效应，即根据温度单独预测的新陈代谢过程会减缓。我们检验了这样一个假设，即在广温性淡水浮游甲壳动物中，遗传或可塑的耐热性差异可以通过代谢补偿来解释。我们在一系列测定温度（5-37°C）下的 ramp-up 实验中测量了 8 种 的呼吸速率，这些 代表了先前报道的急性耐热性的一系列差异，并且在更窄的温度范围内（10-35°C），在具有不同驯化历史的 中进行了测量（分别为 10°C 或 25°C）。我们发现耐热和热敏基因型之间的温度特异性呼吸率没有差异。相比之下，我们观察到在研究温度范围内的两个极端都存在呼吸率的适应特异性补偿差异。值得注意的是，与 10°C 驯化的对照相比，在 25°C 驯化的 中，氧气消耗在较高温度下减速，这在活动动物中观察到，这种模式得到了过滤率相似变化的证实，部分得到了线粒体膜电位变化的证实。恢复实验表明，呼吸减少不是由于在亚致死温度下暴露造成的不可逆损伤。为了适应高温而获得呼吸调节所需的响应时间比适应低温的时间要短，这表明在低温下的代谢补偿需要较慢的、可能是结构性的变化。
