Basal metabolic rate, maximum thermogenic capacity and aerobic scope in rodents: interaction between environmental temperature and torpor use

摘要

When torpid animals arouse and warm up to restore normal body temperature (T-b), they produce heat at levels that can reach up to 10 times basal metabolic rate (BMR), close to the cold-induced summit metabolism (VO2-sum). Because torpor is an adaptation aimed at conserving energy over periods of low ambient temperature (T-a) and food availability, selective forces that have led to the evolution of torpor may have simultaneously favoured high thermogenic capacity (i.e. VO2-sum) relative to the maintenance costs (i.e. BMR), hence a higher factorial aerobic scope (FAS; the ratio of VO2-sum to BMR). My objective was to test this adaptive hypothesis using a phylogenetically informed comparative approach with data on BMR and VO2-sum in rodents. I found a strong negative correlation between FAS and the average of the daily minimum T-a (T-min) in species using torpor, which was due to differential effects of T-a on BMR (but not VO2-sum) in species that use torpor compared with species that do not. In addition, FAS was negatively correlated with the lowest torpid T-b in a subset of nine species. These results suggest that in species using torpor, selective forces may have acted to maximize the efficiency of thermogenic capacity (VO2-sum) relative to maintenance costs (BMR), resulting in an increasing FAS with decreasing T-a.