Body Temperature Variability in the Australian Water Rat, Hydromys chrysogaster, in Air and Water

Abstract

Body and skin temperatures were recorded from water rats exposed to a range of air temperatures and also immersed in water at various temperatures. They were able to maintain stable core temperatures (mean 36.1°C, SD 0.65, n=61) at air temperatures up to 30°C. At 35°C they were unable to avoid hyperthermia despite their use of saliva spreading to enhance heat loss. Regional heterothermia was observed both in air and in water, but water rats were unable to maintain deep body temperatures at water temperatures lower than 25°C. Variations in the level of activity in cold water affected the rate of heat loss. Examination of the vascular system revealed the presence of various networks adapted for heat loss, but no major heat-conserving vascular retia. It is suggested that the poor thermoregulatory performance of water rats during aquatic excursions is largely due to the lack of heat-conserving retia, and to the poor insulative capacity of the fur when wet. The platypus, which possesses excellent fur insulation and a highly developed heat-conserving system, is a very competent homeotherm in cold water. The behavioural responses displayed by water rats which enable them to exploit the aquatic environment in south-eastern Australia are discussed.