Allometric scaling of maximum metabolic rate: the influence of temperature

1. Maximum aerobic metabolic rate, measured in terms of rate of oxygen consumption during exercise ( [graphic removed] ), is well known to scale to body mass (M) with an exponent greater than the value of 0·75 predicted by models based on the geometry of systems that supply nutrients. 2. Recently, the observed scaling for [graphic removed] ([is proportional to]M⁰·⁸⁷²) has been hypothesized to arise because of the temperature dependence of biological processes, and because large species show a greater increase in muscle temperature when exercising than do small species. 3. Based on this hypothesis, we predicted that [graphic removed] will be positively related to ambient temperature, because heat loss is restricted at high temperatures and body temperature is likely to be elevated to a greater extent than during exercise in the cold. 4. This prediction was tested using a comparative phylogenetic generalized least-squares (PGLS) approach, and 34 measurements of six species of rodent (20·5-939 g) maximally exercising at temperatures from -16 to 30 °C. 5. [graphic removed] is unrelated to testing temperature, but is negatively related to acclimation temperature. We conclude that prolonged cold exposure increases exercise-induced [graphic removed] by acting as a form of aerobic training in mammals, and that elevated muscle temperatures of large species do not explain the scaling of [graphic removed] across taxa.