Effect of Exogenous Cortisol on Mortality of a Dasyurid Marsupial

Departments of *Physiology and †Zoology, Monash University, Clayton, Victoria 3168, Australia (Received 19 December 1974) In the shrew-like marsupial Antechinus stuartii from eastern Australia, there is an abrupt and total mortality of males after a 7 to 10-day mating period in August or September (Woolley, 1966; Wood, 1970). Males isolated in the laboratory before mating survive beyond the time of natural mortality (Wood, 1970). Barnett (1973) observed increased peripheral corticosteroid concentrations in males taken from natural populations in the last weeks of life. To test whether this change could be a cause of the mortality, exogenous cortisol was injected into laboratory-held males. Male A. stuartii were captured before the mating period in July 1973 and 1974 at Powelltown, Victoria, and caged singly under the natural Melbourne photoperiod. Their average initial body weight was 30·1 ± 3·6 g (n = 38). In each year they were divided into three groups: two