Metabolic Responses of a Fossorial Rodent (Spalax ehrenbergi) to Simulated Burrow Conditions

Abstract

Mole rats (Spalax ehrenbergi) are rodents morphologically adapted to fossorial life. Their subterranean galleries are common in heavy and wet soils where hypoxia and hypercapnia are likely to prevail. Nevertheless, animals have often been observed to be intensively active under these conditions. In chronic experimental exposure to increasing hypoxia and hypercapnia, mole rats kept their initial body mass down to PO₂ = 42 torr and PCO₂ = 100 torr. White rats began losing weight at PO₂ = 96 torr and PCO₂ = 50 torr, the final weight loss being 73% of the initial body mass. Resting M of mole rats in acute exposure to a simultaneous decrease of O₂ and increase of CO₂ remained constant down to PO₂ = 33 torr. The white rats, however, failed to maintain their Mrest at a PO₂ lower than 42 torr. Mole rats, electrically stimulated to activity, maintained their augmented M (at a level three times the resting value) down to PO₂ = 75 torr. The white rats' similarly augmented M started to be PO₂ dependent at PO₂ = 130 torr. The active mole rats consume O₂ at a rate above that of resting level down to 27 torr, which is below their Pc = 33 at rest. When exposed to low temperature (Ta = 10 C and 20 C), white rats failed to respond to Ta = 20 C at PO₂ = 65 torr and to Ta = 10 C at PO₂ = 41 torr. Mole rats exposed to cold at PO₂ = 65 torr consumed O₂ at the same rate as in air. Critical PO₂s for the mole rats were found to be lower than for any other rodent studied so far. An equation which enables prediction of the metrbolic rate at different combinations of hypoxia and Ta is suggested. The metabolism of mole rats was found to be relatively unaffected by hypoxic-hypercapnic conditions, thus showing functional adaptations to fossorial life. In this ability to withstand hypoxic conditions, they exceed even mammals of the highest altitude studied so far.