Ecophysiology of a Wild-Living Population of the Velvet-Furred Rat, Rattus Lutreolus Velutinus (Rodentia: Muridae), in Tasmania

Abstract

Plasma corticosterone (B) concentrations and certain haematological and morphological parameters were measured in an age cohort of velvet-furred rats, Rattus lutreolus velutinus, in Tasmanian wet sclerophyll forest. Individuals were trapped repeatedly and sampled sequentially for 14 months, offering an opportunity to derive morpho-physiological profiles for free-living individuals. Throughout the study, 130 blood samples were obtained from 29 individuals from the cohort. Gender differences were detected, with total plasma B concentration in females exceeding that in males significantly during the breeding season. By partitioning the total B concentration into biologically active and inactive fractions, it is demonstrated that whilst female rats had higher B levels 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 proportion of biologically active steroid actually increased. These data confirm the breeding season as a stressful period for males. Gender differences also were detected for mean white blood cell counts, being higher in males at all times. No gender-linked differences were detected for plasma protein concentration, red blood cell counts, haematocrif haemoglobin concentration or derived parameters. Physiological data are related to a body condition index and combined with observations made throughout the study of tail wounding and excessive ectoparasite burdens to present a morpho-physiological profile for R.l. velutinus active in wet sclerophyll forest.