Comparing the Temperature Dependence of Mitochondrial Respiration among Vertebrates

Background: The metabolic theory of ecology (MTE) has often assumed that the temperature dependence of whole-organism respiration rate reflects only the biochemical kinetics of individual mitochondria summed across tissues. This assumption does not incorporate the many well-documented structural or functional changes in mitochondria that species may undergo to overcome, at least partially, thermodynamic constraints via acclimation. Yet, the validity of this basic assumption has scarcely been examined at broad scales. Objective: We examine the temperature dependence of mitochondrial respiration in vitro across diverse vertebrates (fishes, mammals, birds, and amphibians) over a broad temperature range. We then compare this relationship to the temperature dependence of whole-organism respiration rate both within and across species. Results: Despite differences in the quantity and composition of substrate, temperature alone explains the majority of variation in mitochondrial respiration rate across species. Also, respiration rate is similarly related to temperature at the level of mitochondria, within species at the level of whole organisms, and across species at the whole-organism level. These results contradict predictions based on the metabolic cold adaptation hypothesis, which rests on the assumption that adaptations allowing species to perform at higher levels in colder environments are of primary importance. Still, phylogeny and species identity explained between 7% and 16% of variance at the whole-organism level. Conclusion: The biochemical kinetics of mitochondrial respiration in vertebrates is largely conserved across species and environments, irrespective of adaptation or acclimatization.