Ambient temperature cycles entrain the free-running circadian rhythms of the stripe-faced dunnart,Sminthopsis macroura

Summary We examined the effect of cycles of 12 h warm (35 ± 2 °C) and 12 h (21 ± 2 °C) ambient temperature (Ta) upon the circadian activity rhythms of stripe-faced dunnarts, Sminthopsis macroura, free-running in conditions of constant dark (DD) or constant light (LL). It was hypothesized that dunnarts would entrain to the temperature cycles (TaHLs) or show perturbations of period, and that LL would act synergistically with the TaHLs in these effects. Under DD, 2 of 6 animals showed clear entrainment to the TaHLs. Other animals exhibited changes of period () and heavy negative masking of activity during the warm fraction of the TaHLs. Under LL, 3 of 12 animals entrained to the TaHLs. It was concluded that Ta is a significant though weak Zeitgeber for S. macroura compared to light. It is possible that TaHLs entrain homeotherm activity rhythms by altering the rhythm of body temperature, which is usually tightly coupled to activity.Abbreviations TaHL a cycle of Higher and Lower ambient temperature - TaC Constant Ta - Tb body temperature