Atypical behavioural, metabolic and thermoregulatory responses to hypoxia in the naked mole rat (Heterocephalus glaber)

Hypoxia compromises aerobic energy production at the cellular level, but hypoxic environments are commonly encountered by mammals. In response, mammals typically exhibit compensatory physiological and behavioural adaptations that help to restore energetic homeostasis by reducing physical activity and body temperature (T-b) to lower metabolic demand. Naked mole rats (NMRs; Heterocephalus glaber) are among the most hypoxia-tolerant mammals identified but their behavioural and thermal responses to acute hypoxia are poorly characterized. Using behavioural tracking software, we examined the effects of acute hypoxia (1h at 7% O-2) on physical activity and T-b in animals held at their natural burrow temperature (30 degrees C), or at temperatures above (38 degrees C) or below (20 degrees C). In separate experiments, we used respirometry to measure metabolic rate under the same conditions. Physical activity decreased similar to 26-60% and T-b decreased by similar to 1.9-3.7 degrees C during hypoxia in all temperatures. Normoxic metabolic rate was highest at 20 degrees C, but was suppressed to similar rates in hypoxia across all temperatures. When animals were given the opportunity to escape their burrow temperature to either warmer or colder chambers during the hypoxic episode, NMRs surprisingly avoided the cold chamber, suggesting they are unable to take advantage of anapyrexia. Conversely, NMRs were able to use behavioural thermoregulation to maintain T-b in hypoxia when given the choice of temperatures within and above their burrow temperature. Taken together, these findings indicate that NMRs respond to acute hypoxia with reversible decreases in physical activity, T-b and metabolic rate across a range of ambient temperatures to reduce oxygen requirements.