Effect of Water Balance on Thermoregulation in Waterproof Frogs (ChiromantisandPhyllomedusa)

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Abstract
Arboreal frogs of the genera Chiromantis and Phyllomedusa generally have low evaporative water loss (EWL) but can regulate water loss to maintain body temperature ( ) at about 40 C at high ambient temperatures ( ). Thermoregulatory responses of these animals were tested in a thermal gradient and in a wind tunnel to determine whether these responses were affected by the water balance of the animal Hydrated frogs maintained higher in the thermal gradient and frequently employed physiological thermoregulation (enhanced EWL) rather than move away from the heat source. When deprived of water they maintained lower and rarely employed evaporative cooling. When subjected to high in a wind tunnel, regulated was significantly lower (and EWL correspondingly higher) in animals having water reserves in their bladders. Infusion of water into frogs initially lacking bladder reserves decreased and increased EWL in both species. Infusion of hyperosmotic NaCl into hydrated animals increased and reduced EWL markedly in Chiromantis but resulted in only a slight rise in in Phyllomedusa. These frogs resemble other thermoregulating vertebrates in that both behavioral and physiological responses to heat are influenced by hydration state with the result that water is conserved when in short supply.