No rest for the rodent: energy management strategies in the naked mole-rat

Organisms have access to a limited amount of energy that must be distributed among multiple physiological processes. Broadly, the total daily energy expenditure (DEE) can be partitioned into maintenance costs (i.e., resting metabolic rate RMR) and active energy expenditure (AEE). The slope (b) between DEE and RMR provides insights into energy management strategies. In the additive model, where changes in activity are independent of maintenance energy, DEE and RMR follow a part-whole relationship with b=1. In the allocation model, where increased activity requires compensatory reductions in maintenance costs, a limit on DEE causes a DEE-RMR relationship with b<1. In the performance model, increased activity causes an increase in maintenance costs, which causes a DEE-RMR relationship with b>1. Despite their high lifetime energy expenditure and resistance to age-related metabolic decline, energy management is yet to be explored in the African naked mole-rat (NMR, Heterocephalus glaber). To investigate metabolic strategies in the NMR, repeated metabolic and activity measurements were taken in 32 individual NMRs using a multiplexed metabolic system. DEE was not repeatable, thus the DEE-RMR covariance at the among-individual level could not be fitted. At the within-individual level, however, the positive correlation between RMR and activity and the DEE-RMR relationship with b > 1 indicated support for the performance model. Hence, our results indicate that within-individual changes in activity and RMR are associated, suggesting that when a NMR increases activity on a given day, the impact on DEE are disproportionate because of a concurrent increase RMR.