The seasonal physiology of 'Antechinus stuartii': renal and gonadal correlates

Abstract

'Antechinus stuartii' is a small marsupial that has an unusual life history pattern. It includes a highly synchronised brief mating period occurring at the same time every year within a particular population. Following the mating period all males die from an uncontrolled stress response, which is associated with high plasma concentrations of glucocorticoids and testosterone. Seasonal changes in renal structure and function, and their contributions to male mortality were investigated. Changes in the reproductive tract were also assessed. Following the seasonal study, changes in renal structure and function and reproductive tract were assessed in males given depot injections of either saline, testosterone only, cortisol only or testosterone plus cortisol at doses mimicking those found in the mating period. Glomerular filtration rate (GFR) changed seasonally, with GFR of males lower in July and August, and that of females lower only in the premating period. Plasma sodium and chloride levels were higher, and potassium levels were lower in July and August in both sexes. GFR decreased following testosterone treatment, independent of cortisol. Urinary electrolytes, osmolality, and urea significantly decreased in all cortisol treated animals. Plasma potassium and chloride were affected by the administration of cortisol. ... The present study has demonstrated that there are seasonal changes in renal structure and function in male 'A. stuartii', and these changes were mimicked by the administration of testosterone, with less influence from cortisol administration. The accessory reproductive tract was also sensitive to these hormones. This study demonstrates that the synchronous seasonal changes that occur in 'A. stuartii' are not confined to the reproductive tract, and the changes are governed less by cortisol, than by the sensitivity of 'A. stuartii' males to testosterone.