Temperature and dehydration effects on metabolism, water uptake and the partitioning between respiratory and...

Terrestrial anurans often experience fluctuations in body temperature and hydration state, which are known to influence evaporative water loss through the skin (EWL_Skin) and lungs (EWL_Resp). These effects arise from associated changes in skin permeability, metabolism and lung ventilation. Herein, we determined the rates of EWL_Skin and EWL_Resp in the terrestrial toad Rhinella diptycha at different temperatures and hydration states. We measured oxygen uptake rates to verify whether alterations in the partitioning between EWL_Skin and EWL_Resp were associated with metabolism-induced changes in pulmonary gas exchange. We also measured the influence of hydration and temperature on water uptake (WU) through the skin. Finally, as estimates of skin resistance to evaporation (R_s) are usually inferred from total evaporative water loss (EWL_Total), under the assumption of negligible EWL_Resp, we calculated the potential error in accepting this assumption for different temperature and hydration states. EWL_Skin and EWL_Resp increased with temperature, but this response was greater for EWL_Resp, which was attributed to the temperature-induced elevation in metabolism and lung ventilation. Dehydration caused a decrease in the relative contribution of EWL_Skin to EWL_Total, mirrored by the concurrent increase in the contribution of EWL_Resp, at all temperatures. Thus, R_s increased with dehydration. WU rates were dictated by dehydration with little influence of temperature. The partitioning between EWL_Skin and EWL_Resp was affected by both temperature and hydration state and, under some conditions, considering EWL_Resp as negligible led to significant errors in the assessment of skin resistance to evaporation.