Influence of temperature on evaporative water loss and cutaneous resistance to water vapour diffusion in the orange-thighed frog (Litoria xanthomera)

Abstract

We evaluated the effect of ambient temperatures between 25 and 43°C on the rate of evaporative water loss (EWL) in eight adult Litoria xanthomera (average body mass = 7.3 ± 0.6 g). Frogs were placed in a cylindrical chamber that permitted them to fully conceal their ventral surfaces using a water-conserving posture. Their EWL was 7.1 ± 0.7 mg g–1 h–1 at 25°C and reached 28.0 ± 2.5 mg g–1 h–1 at 43°C. Agar replicas of the frogs were used to evaluate boundary-layer resistances associated with the EWL measurements and, thus, to permit evaluation of cutaneous resistance to vapour diffusion (rc) in live frogs. The rc of L. xanthomera was stable over the temperature range of 25–35°C, averaging about 28 s cm–1, and then declined stepwise with ambient temperatures above 37°C. The highest rc recorded for each individual over the range of temperatures studied averaged 32.0 ± 1.2 s cm–1. The thermolabile nature of rc demonstrates a well developed thermoregulatory control of EWL in this species, a trait very similar in pattern and extent to that previously measured in the closely related Litoria chloris.