Bioenergetics, thermoregulation and urine analysis of squirrels of the genus Xerus from an arid environment

Abstract

A comparative thermoregulatory and bioenergetic study including urine analyses of two species of southem African ground squirrels from the genus Xerus was carried out. Both X princeps (a rock dweller) and X Inauris (a burrow dweller) are well adapted to a hot and arid environment. Both species have low resting metabolic rates (RMR) and high conductances (C). In X princeps RMR Is lower and C Is higher relative to X inauris. Both species can increase their body temperature (T b) In their thermoneutral zones and In ambient temperatures (T.) above this. Salivation In both species was observed only at T. = 38°C. At T. = 5°C X princeps Increase their oxygen consumption significantly ct. X Inauris (p < 0, 005) and regulated their T bat 36, 1 � O, 5�C while X Inauris maintained T b at 34, 8 � 0, 6�C. Nonshivering thermogenesis was measured as maximal V02 and T b of anaesthetized squirrels injected with noradrenaline (NA). X Inauris and X princeps responded to NA by Increasing V~ and T b. Both species show a low digestible dry matter intake as predicted for desert rodents. In both squirrels percentage moisture in faeces is low but significantly (p < 0, 05) lower In X princeps than In X Inauris. Urine analyses of hydrated squirrels showed that in X inauris urea and Mg+ + concentrations were significantly higher ct. X princes (p < 0, 05; p < 0, 01).