Sex, season and melatonin administration affects daily activity rhythms in a marsupial, the brown antechinus, 'Antechinus stuartii'

The carnivorous marsupial 'Antechinus stuartii' relies on photoperiodic changes to time reproductive activities, including behaviour, in spring. Similar to other mammals, the administration of the hormone melatonin is known to affect the synchronisation of reproduction in 'A. stuartii'. The present study sought to explore the alterations in locomotor activity from the winter solstice in both males (body mass 35 g) and females (body mass 20 g) as a result of the influences of the changes in the natural photocycle and also of melatonin administration while under the natural photocycle. The total daily activity was found to differ between sexes, with males more active than females, irrespective of melatonin or control treatments. Daily activity patterns were significantly different between male groups but not female treatment groups. Activity patterns were also found to differ between males and females. The significance of these differences is discussed with relation to the profound psychological differences between the sexes, in this mammal where an irreversible stress response is part of the complete post-mating mortality of all males, but not females.