Heat production and dissipation in golden spiny mice, Acomys russatus from two extreme habitats

1. A comparative study of heat production and heat dissipation in two populations of golden spiny mice (Acomys russatus) from two extremely different habitats was carried out. 2. Mice from a hot environment, the shores of the Dead Sea (Ein Gedi, EG-mice) could not maintain body temperature (T_b) when exposed to ambient temperature (T_a) of 6 °C in a cold room. Mice from a colder environment, the high mountains of South Sinai (S-mice), acclimated in the laboratory to 28 °C or freshly captured, were able to thermoregulate in a cold room (T_a=6 °C). 3. Mice of both populations, acclimated to 28 °C, had the same resting oxygen consumption ( {Mathematical expression}) in the thermoneutral zone (0.75 ml O₂ (g·h)^-1 for 60 g mean body weight). 4. {Mathematical expression} at T_a below 20 °C showed differences. In S-mice it continued to rise and enough heat was generated to keep them euthermic. EG-mice showed a progressive decrease and could not maintain T_b. 5. Continuous measurements of T_b and {Mathematical expression} in EG-mouse during cooling (T_a=6 °C) and reheating (T_a=25 °C) show smooth curves without any bursts of heat generating activity typical of rodents entering or coming out of torpor. The spiny mice have to be rewarmed by an external heat source. 6. Thermal conductance was measured in live mice after acclimation to 28 °C or in carcasses collected in the field at various seasons. Measurements failed to show any appreciable difference between the two populations where animals with similar body weight were compared. 7. It is concluded that difference in heat production and not in heat conservation enable Acomys russatus to adapt to a colder habitat.