Naked Mole Rats Exhibit a Consistently Low Resting Metabolic Rate with Aging
Across mammalian species, resting metabolic rate roughly inversely correlates with species life span and body weight. Larger species are on average longer lived and have lower metabolic rates. There are, of course, a number of interesting outliers that exhibit very long lives relative to similarly sized mammalian species, such as a few bat species and the naked mole-rats that are the subject of this paper. The prevalent thinking on the matter of metabolic rate and longevity is that this relationship says something about the amount of oxidative damage an individual's cells can sustain, or the capacity of those cells to resist that form of damage. Greater metabolic rate implies greater generation of oxidative molecules by mitochondria. The membrane pacemaker hypothesis on species life span suggests that the degree to which the lipid composition of cell membranes can resist oxidative damage is important. There is a great deal of complexity under the hood here, however, and every neat and compact theory on important mechanisms in this matter has its exceptions and outlier species.
This study offers a detailed analysis of resting metabolic rate (RMR) in naked mole-rats, incorporating individual, social, and colony-level factors to clarify how energy expenditure is organised within a eusocial mammal. Body mass consistently emerged as the primary predictor of RMR, aligning with the well-established allometric scaling of metabolic rate across mammals. This follows widely accepted convention that body mass explains the majority of variation in mammalian metabolic rates.
Notably the absolute RMR values recorded here are substantially lower than those predicted for mammals of similar size, further supporting the characterisation of naked mole-rats as possessing an unusually low metabolic profile. Predicted RMR values from 10 different studies and their associated approaches show a range of RMRs from 51.6 ml O2/hr to 71.1 ml O2/hr, compared to an average RMR of 45.5 ml O2/hr in the present study. This metabolic depression is commonly viewed as an adaptation to their subterranean environment, where relatively stable burrow temperatures lessen thermoregulatory demands, and energetic efficiency is advantageous given the high energetic and water costs of excavation alongside constrained resource availability. Within this ecological framework, reducing maintenance energy expenditure is likely to contribute both to colony stability and to the species' exceptional longevity.
Age did not significantly predict RMR once body mass was accounted for. The absence of an age effect is particularly notable given the exceptional lifespan of naked mole-rats. In many mammals, aging is accompanied by measurable shifts in metabolic maintenance; here, basal metabolism appears remarkably stable across age classes. This stability is consistent with the species' negligible senescence phenotype and suggests that aging does not impose detectable energetic costs at the level of resting metabolism.