Heat production in nocturnal (Praomys natalensis) and diurnal (Rhabdomys pumilio) South African murids
Heat production by means of oxygen consumption (Vo2) was measured at different ambient temperatures (Ta 6-34 °C in both species. The thermoneutral zone for both species was found to be at Ta = 32 ± 1 °C. Below the lower critical point Vo2 for the diurnal species (R. pumilio) was significantly higher (p<0,001) than Vo2 for the nocturnal species (P. natalensis). Non-shivering thermogenesis (NST) was measured as a response to an injection of noradrenaline (1,5 mg/kg s.c.) in both species and NST magnitude for R. pumilio was significantly higher (p<0,001) when compared to P. natalensis. The differences in heat production are related to the difference in fur insulation and this may derive from the fact that R. pumilio is diurnal while P. natalensis is nocturnal.