Shifts in thermoregulatory patterns with pregnancy in the poikilothermic mammal—The naked mole-rat ( Heterocephalus glaber)

Abstract

1. 1. The naked mole-rat ( Heterocephalus glaber) is a poikilothermic mammal. During gestation metabolic shifts that differ from both mammalian and reptilian thermoregulatory patterns occurred. 2. 2. Body temperature was directly dependent on ambient temperature. At low ambient temperatures the temperature differential ( T b − T a) was approximately 3°C, whereas at higher ambient temperatures the temperature differential diminished. 3. 3. In early pregnancy (prior to week 3) oxygen consumption at low ambient temperatures was greater than that of non-reproductive animals. A maximal metabolic rate (3.2 ± 1.0 ml O 2 . g −1 . h −1) occurred at an ambient temperature of 27°C. Thereafter the endothermic pattern of metabolism with increasing ambient temperatures was evident. Oxygen consumption decreased with increasing ambient temperature to minimal rates of 1.2 ± 0.1 ml O 2 . g −1 . h −1 over the ambient temperature range of 31–34°C. 4. 4. Oxygen consumption in late pregnancy (1.8 ± 0.1 ml O 2 . g −1 . h −1) was not correlated with ambient temperature over the entire ambient temperature range measured (24–36°C). 5. 5. Differences in thermoregulation in early and late pregnancy may be attributed to different rates of heat loss as a consequence of (a) changes in surface area and body mass or (b) vascular changes. Furthermore the thermoregulatory changes in late pregnancy may indicate that maximal overall metabolic capacity had been reached, for peak resting metabolism (expressed per animal rather than per gram body mass) in early pregnancy was similar to observed metabolism in late pregnancy. 6. 6. The dissociation of metabolism from both ambient temperature and body temperature in late pregnancy could confer an energetic advantage to this arid dwelling underground inhabitant; for it may enable the breeding female to partition a greater portion of available energy into reproduction.