Seasonal Changes in Organ Weights of Rattus villosissimus during the 1966-69 'Plague' at Brunette Downs, Northern Territory

Abstract

Six samples of R. villosissimus were collected at Brunette Downs, N.T., between December 1967 and April 1969. The body weight of both sexes showed marked seasonal variation. It was highest in March 1968, when there was plenty of green grass for the rats to eat, but as the grass dried off, it fell to a minimum in November 1968 and rose again after the 1968-69 wet season. There is some evidence that the growth of the rats in the paddocks was retarded during 1968 because of lack of food. The weight of most organs was strongly correlated with body weight and therefore showed the same seasonal fluctuations. The pattern persisted even when the variates were adjusted for differences in body weight. In March 1968 the rats of both sexes had large spleens, perhaps in response to a high ectoparasite load. Adrenal weight showed the same seasonal trends as the other organs. Chronic inanition apparently did not cause adrenal hypertrophy. High adrenal weights of female rats coincided with the 1967-68 and 1968-69 breeding seasons.