Interspecific variation in thermoregulation among three sympatric bats inhabiting a hot, semi-arid environment

Abstract

Bats in hot roosts experience some of the most thermally challenging environments of any endotherms, but little is known about how heat tolerance and evaporative cooling capacity varies among species. We investigated thermoregulation in three sympatric species (Nycteris thebaica, Taphozous mauritianus, and Sauromys petrophilus) in a hot, semi-arid environment by measuring body temperature (Tb), metabolic rate and evaporative water loss (EWL) at air temperatures (Ta) of 10 - 42 °C. S. petrophilus was highly heterothermic with no clear thermoneutral zone, and exhibited rapid increases in EWL at high Ta to a maximum of 23.7 ± 7.4 mg g-1 hr-1 at Ta ≈ 42 °C, with a concomitant maximum Tb of 43.7±1.0 °C. T. mauritianus remained largely normothermic at Tas below thermoneutrality, and increased EWL to 14.7 ± 1.3 mg g-1 hr-1 at Ta ≈ 42 °C, with a maximum Tb of 42.9 ± 1.6 °C. In N. thebaica, EWL began increasing at lower Ta than in either of the other species, and reached a maximum of 18.6±2.1 mg g-1 hr-1 at Ta = 39.4 °C, with comparatively high maximum Tb values of 45.0±0.9°C. Under the conditions of our study, N. thebaica was considerably less heat tolerant than the other two species. Among seven species of bats for which data on Tb as well as roost temperatures in comparison to outside Ta are available, we found limited evidence for a correlation between overall heat tolerance and the extent to which roosts are buffered from high Ta.