Cutaneous gas exchange and low evaporative water loss in the frogsPhyllomedusa sauvagei andChiromantis xerampelina

Summary

• 1. Pulmonary and cutaneous gas exchange and cutaneous evaporative water loss (EWL) were measured in two frog species,Phyllomedusa sauvagei andChiromantis xerampelina, at 24±1.5°C. These xeric-adapted frogs are noted for their very low EWL.

• 2. Fractional cutaneous gas exchange varies directly with cutaneous EWL inP. sauvagei. At EWL rates typical of restingP. sauvagei, cutaneous gas exchange is of minor importance. Fractional cutaneous gas exchange is also low in restingC. xerampelina.

• 3. Fractional gas exchange through the skin in restingP. sauvagei andC. xerampelina is similar to that in terrestrial reptiles but only about 1/12th the fractional CO₂ elimination and 1/7th the fractional O₂ uptake of typical anuran amphibians.

• 4. Blood$P_{{\text{CO}}_{\text{2}} }$, pH and HCO ⁻₃ inP. sauvagei are like those in other anurans with permeable skins. We conclude thatP. sauvagei hyperventilates relative to most other anurans.

• 5. The reduced cutaneous gas exchange inP. sauvagei andC. xerampelina is the result of a general reduction in skin permeability. As in reptiles, the reduced permeability is of primary importance for maintaining H₂O balance while the concomitant loss of cutaneous gas exchange has little functional significance.