Effect of water restriction on temperature regulation of the fruit-bat Rousettus aegyptiacus

1. The thermoregulatory responses of the fruit-bat, Rousettus aegyptiacus, the only fruit-bat out of 32 bat species in Israel, were studied over a wide range of ambient temperature during normal hydration and during water restriction.2. The thermoneutral zone of the normally-hydrated fruit-bat ranged between 31-36°C. Oxygen consumption in this range averaged 0.95 ± 0.15 mlg-1h-1.3. Evaporative water loss and respiration frequency during normal hydration incrased as power functions of ambient temperature and were significantly correlated (P < 0.02). The normally-hydrated, heat exposed fruit-bat effectively regulated its body temperature and dissipated the total metabolic heat production by evaporative cooling.4. In bats fed on oven-dried apples (water restriction), body mass decreased by 20.72 ± 2.78%. Oxygen consumption between 32-36°C increased significantly and body temperature was relatively high. Evaporative water loss decreased sinificantly, except at 36°C where evaporative water loss was not significantly different from that during normal hydration, suggesting the preference for body temprature regulation at the cost of increased water loss. At this ambient temperature, dry thermal conductance increased significantly compared to normal hydration, facilitating non-evaporative heat loss.5. We conclude that the Israeli population of Rousettus aegyptiacus is adapted to the relatively warm climate and can cope with a decreased water content in its exclusive fruit diet and effectively regulate its body temperature and metabolic rate.