O2-uptake, thermoregulation and heart rate in the springhare (Pedetes capensis)

Abstract

1. O2-consumption (O2), rectal temperature (Tre) and heart rate were measured in two adult springhares (♂,♀; body mass 2.2–2.4 kg) at ambient temperatures (Ta) from 6–35 °C. Abdominal temperature in the female and heart rate in both animals were determined by telemetry. 2. AtTa's from 23–28 °C rectal temperature in both animals ranged between 35.5–36.3 °C. This range was well maintained at lowTa's. Exposure to highTa's, however, led to a considerable rise of the rectal temperature (to above 39 °C atTa=35 °C). 3. The lowest oxygen uptake (0.32–0.37 ml O2·g−1·h−1) was found between 23–33 °C. This is only 65–75% of the predicted value in similar sized mammals. Below 23 °C O2-consumption increased rapidly up to approximately 2,5 times (6–7 °C) the value in the thermoneutral zone (23–33 °C). AtTa's above 33 °C the heat dissipating capacities of the springhares proved to be inadequate and consequentlyTre rose steadily. 4. Basal heart rate (75–85 beats·min−1) was about 30% below the standard value for similar sized mammals. During exposure to cold the heart rate sometimes exceeded 200 beats·min−1. 5. The measured parameters are discussed with special regard to the extent of the springhare's adaptation to arid conditions. It is concluded that these rodents are physiologically adapted to fossorial habits rather than to life in desert environments and are thus restricted to semi-arid areas.