Endocrine changes in dasyurid marsupials with differing mortality patterns

Abstract

A comparison was made between the breeding-related endocrine changes in two species of dasyurid marsupial ( Antechinus swainsonii and A. flavipes), which exhibit a catastrophic male mortality after a brief mating period; and those of another dasyurid species ( Sminthopsis crassicaudata), the males of which survive an extended breeding period. In the males of both Antechinus species, the mating period was preceded by a rapid rinse in plasma androgen concentration and accompanied by a marked fall in plasma corticosteroid-binding globulin (CBG) concentration, to less than the total glucocorticoid concentration, which itself rose. As a consequence plasma free glucocorticoid concentration rose approximately 10-fold just before the males disappeared from the populations. Severe hemorrhagic ulceration of the upper digestive tract was consistently found soon after capture near the time of mating. In females, CBG concentration was always well in excess of total glucocorticoid concentration and free glucocorticoid concentration remained low. There was a significant negative correlation between plasma androgen and CBG concentrations in male Antechinus species from the natural populations. In laboratory-held castrate male A. swainsonii, injection of either testosterone or dihydrotestosterone caused a dose-related fall in CBG. In contrast to the above, the CBG concentration was always well in excess of total glucocorticoid concentration in the plasma of male S. crassicaudata and there was no evidence of interaction between plasma androgen and CBG concentration. These findings support the hypothesis that, in those species with a breeding-related mortality of males, an androgen-dependent fall in plasma CBG concentration and a stressful mating period result in death from adrenocortical suppression of the immune and inflammatory responses.