Phase-response curve to 1-hour light pulses for the marsupial, Dasyuroides byrnei

Most Australian marsupials are nocturnal and consequently it might be expected that the circadian system of this group may be similar to the circadian system of nocturnal rodents. Ten male kowaris (Dasyuroides byrnei) were allowed to free-run in constant darkness and were subsequently administered 1-hour light pulses (1000 lux) at known circadian times in their cycles at intervals of greater than 2 weeks. Changes in the phase of the kowari's circadian rhythm of wheel-running were measured when their rhythms reached a new steady-state after each light pulse and these data were used to construct a phase-response curve to light for the species. The kowari PRC exhibited essentially the same characteristics as those reported for the nocturnal rodents and the marsupial species Sminthopsis macroura. It appears that the kowari entrains its circadian rhythms to light/dark cycles via the discrete phase shifting mechanism as described in nocturnal rodents.