THERMOREGULATION AND METABOLIC ACCLIMATION IN THE NATAL MOLE-RAT (CRYPTOMYS HOTTENTOTUS NATALENSIS) (RODENTIA, BATHYERGIDAE)

The social Natal mole-rat Cryptomys hottentotus natalensis has a mean (+/- S.D.) resting metabolic rate (RMR) when newly captured of 1.03 +/ - 0.25 cm(3) O-2 g(-1) h(-1) (n = 7) at an ambient temperature (Ta) of 30 degrees C, within the thermoneutral zone (TNZ) of 30-31.5 degrees C. Two months after maintenance in the laboratory at 26 degrees C, the RMR of the same animals showed a concomitant drop in value of 20 % at 30 degrees C (TNZ) to a mean of 0.80 +/- 0.12 cm(3) O-2 g(-1) h(-1) ( n = 14), indicating that la6oratory acclimation had occurred. The body temperature of the mole-rat is low 33.4 +/- 0.83 (n = 36) and remains stable at Ta's from 10-30 degrees C. Above 31.5 degrees C, Tb increas es albeit slightly to 35.7 +/- 0.51 degrees C (n = 24). The conductanc e is high 0.13 +/- 0.03 cm(3) O-2 g(-1) h(-1) degrees C-1 (n = 24) at the lower limit of thermoneutrality. The mean RMR at 18 degrees C (the lowest Ta tested) was 1.83 +/- 0.46 cm(3) O-2 g(-1) h(-1), which is 2 .2 times that of the RMR in the TNZ. The nest (where mole-rats rest fo r up to 80 % of the day) is the focal point of the burrow system. The selection for C. h. natalensis to acclimate within its TNZ may relate to seasonal fluctuations in the temperature occurring in the shallow n est, resulting in seasonal acclimatisation in RMR.