ECOPHYSIOLOGY OF A WILD-LIVING POPULATION OF THE VELVET-FURRED RAT, RATTUS-LUTREOLUS-VELUTINUS (RODENTIA, MURIDAE), IN TASMANIA

Plasma corticosterone (B) concentrations and certain haematological an d morphological parameters were measured in an age cohort of velvet-fu rred rats, Rattus lutreolus velutinus, in Tasmanian wet sclerophyll fo rest. Individuals were trapped repeatedly and sampled sequentially for 14 months, offering an opportunity to derive morpho-physiological pro files for free-living individuals. Throughout the study, 130 blood sam ples were obtained from 29 individuals from the cohort. Gender differe nces were detected, with total plasma B concentration in females excee ding that in males significantly during the breeding season. By partit ioning the total B concentration into biologically active and inactive fractions, it is demonstrated that whilst female rats had higher B le vels in the breeding season, most of it was protein bound and inactive . In males, mean total B declined at the onset of breeding but the pro portion of biologically active steroid actually increased. These data confirm the breeding season as a stressful period for males. Gender di fferences also were detected for mean white blood cell counts, being h igher in males at all times. No gender-linked differences were detecte d for plasma protein concentration, red blood cell counts, haematocrif haemoglobin concentration or derived parameters. Physiological data a re related to a body condition index and combined with observations ma de throughout the study of tail wounding and excessive ectoparasite bu rdens to present a morpho-physiological profile for R.l. velutinus act ive in wet sclerophyll forest.