Thermal independence of energy management in a tailed amphibian

The relationship between the minimum metabolic requirements (standard metabolic rate, SMR) and energy costs of non-mandatory physiological functions and behaviour is fundamental for understanding species responses to changing environmental conditions. Theory predicts that ectotherms manage their energy budget depending on whether the relationship between SMR and energy available for other tasks is negative (allocation model), neutral (independent model), or positive (performance model). Energy management has received more attention in endotherms than in ectotherms, where metabolic-behavioural relations may be affected by body temperature variation. We examined the predictions of energy management models at four body temperatures in alpine newts, Ichthyosaura alpestris, under laboratory conditions. High SMR reduced the amount of energy dedicated to food digestion and locomotor activity. The maximum metabolic rate for food digestion was positively related to SMR, while its relationship with locomotor activity was inconclusive. Body temperature affected the intercept but not the slope of these relationships. We conclude that (i) newts manage their energy budget according to the allocation model, (ii) energy management is insensitive to body temperature variation, and (iii) determining energy management models using indirect estimates may be misleading. These findings improve our understanding of the eco-evolutionary significance of SMR variation in tailed amphibians and other ectotherms.