Response to variations in lighting schedules on the circadian activity rhythms in Sminthopsis macroura froggatti (Marsurpialia: Dasyuridae) .

Abstract

The response of Sminthopsis macroura froggatti to alterations in the light-dark cycle was studied in residential mazes that continuously monitored activity. Under a 12: 12 LD cycle S. m. froggatti displayed a predominately nocturnal activity pattern. Most animals spent considerable periods of the light phase in the nest boxes, with only occasional visits to other areas of the mazes. At dark onset there commenced intense activity concentrated mainly in the food and running wheel arms. There was an activity peak early in the dark , with declining levels thereafter. All animals entrained to a phase delay of the LD cycle by delaying the onset of activity each clay until it coincided with lights-out. Rapid entrainment to a reversed photoperiod was achieved within 5 days by phase-delaying activity onset. This species (except for one animal) did not show any unusual variations in the circadian pattern of activity in various LD cycles although there was some evidence for lability in the entrained activity rhythms.