Abstract
Global climatic warming is predicted to drive extreme thermal events, especially in temperate terrestrial environments. Hence, describing how physiological parameters are affected by acute temperature changes would allow us to understand the energy management of organisms facing such non-predictable and constraining events. As mitochondria play a key role in the conversion of energy from food into ATP but also produce harmful reactive oxygen species, the understanding of its functioning is crucial to determine the proximal causes of potential decline in an animal’s performance. Here we studied the effects of acute temperature changes (between 20 and 30°C) on mitochondrial respiration, ATP synthesis rate, oxidative phosphorylation efficiency (ATP/O), and H2O2 generation in isolated liver mitochondria of a terrestrial ectotherm, the common toad (Bufo bufo). Using succinate as the respiratory substrate, we found that the mitochondrial rates of oxygen consumption, ATP synthesis, and H2O2 generation increased as the temperature increased, being 65, 52, and 66% higher at 30°C than at 20°C, respectively. We also found that the mitochondrial coupling efficiency (ATP/O) decreased, while the oxidative cost of ATP production (H2O2/ATP ratio) increased. The present results further indicate that between 40 and 60% of temperature effects on mitochondrial ATP production and H2O2 generation was at minima driven by an action on the oxidative capacity of the mitochondria. These results suggest that B. bufo may need to allocate extra energy to maintain ATP production and protect cells from oxidative stress, reducing the energy allocable performances.
Highlights
Long-term records in climatic data indicate that the global surface temperature has increased by 0.2◦C per decade in the past 30 years (Intergovernmental Panel On Climate Change [IPCC], 2014)
More oxygen was consumed at any steady-state rates of ATP production when the temperature increased, indicating that mitochondrial coupling efficiency decreased with increasing temperature
There was a close correlation between FCCP-induced maximal activity of electron transport system (ETS) and the maximal rate of ATP synthesis and efficiency, indicating that at least 40% of the temperature effects on mitochondrial ATP production and efficiency were driven by an action on the oxidative capacity of the mitochondria (Figure 2)
Summary
Long-term records in climatic data indicate that the global surface temperature has increased by 0.2◦C per decade in the past 30 years (Intergovernmental Panel On Climate Change [IPCC], 2014). Predictions of ever more extreme weather patterns are associated with climate change, especially in terrestrial environments, such as higher frequency and duration of heat waves and heavy rainfall events during the summer in North America and Europe (Fischer and Knutti, 2013; Ummenhofer and Meehl, 2017). The aquatic populations must behaviorally and/or physiologically respond to optimize the performance of individuals under these new conditions (Woodward et al, 2016)
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