THE AMPLITUDE OF CIRCADIAN BODY-TEMPERATURE RHYTHMS IN 3 RODENTS (AETHOMYS-NAMAQUENSIS, THALLOMYS-PAEDULCUS AND CRYPTOMYS-DAMARENSIS) ALONGAN ARBOREAL-SUBTERRANEAN GRADIENT

The maximum amplitudes of circadian rhythms of body temperature (R(t)) of three species of desert rodents inhabiting an arboreal-subterranea n gradient were correlated with habitat-dependent thermoregulatory par ameters such as minimal thermal conductance and the magnitude of ambie nt temperature tolerance by endotherms. It was shown that R(t) differe d by 87-181% of expected values. The data for two rodents (Thallomys p aedulcus and Aethomys namaquensis) that forage aboveground displayed h igher-than-expected R(t) values, whereas the strictly subterranean spe cies (Cryptomys damarensis) had lower-than-expected R(t) values. These data are interpreted in terms of the Endothermic Temperature Range Hy pothesis, which argues that the large range of diel ambient temperatur e fluctuations found in desert habitats may account for the physiologi cal parameters that generate the higher-than-expected body temperature rhythms, a low and fairly inflexible minimal thermal conductance and low resting metabolic rate. Further discussion centres on the possible functional significance of circadian energetic rhythms, particularly in terms of an endotherm's fitness. It is proposed that, at least, fun ctions of the rhythms should be considered: diel thermoregulatory adju stments and energy conservation.