Partitioning of Evaporative Water Loss into Respiratory and Cutaneous Pathways in Wahlberg's Epauletted Fruit Bats (Epomophorus wahlbergi)

The relative contributions of respiratory and cutaneous evaporation to total evaporative water loss (TEWL) and how the partitioning of these two avenues varies with environmental temperature has received little attention in bats. We trained Wahlberg's epauletted fruit bats (Epomophorus wahlbergi) captured in Pretoria, South Africa, to wear latex masks while hanging in respirometry chambers, and we measured respiratory evaporative water loss (REWL) and cutaneous evaporative water loss (CEWL) over air temperatures (T-a) from 10 degrees to 40 degrees C. The bats' normothermic body temperature (T-b) was approximately 36 degrees C, which increased at higher T-a to 40.5 degrees +/- 1.0 degrees C at T-a approximate to 40 degrees C. Both TEWL and resting metabolic rate (RMR) increased sharply at T-a >35 degrees C, with a mean TEWL at 40 degrees C equivalent to 411% of that at 30 degrees C. The increase in TEWL was driven by large increases in both CEWL and REWL. CEWL comprised more than 50% of TEWL over the entire T-a range, with the exception of T-a approximate to 40 degrees C, where REWL accounted for 58% of evaporative water loss. Surface area-specific CEWL increased approximately sixfold with increasing T-a. Thermoregulation at T-a approaching or exceeding T-b involved a considerable energetic cost, with RMR at T-a approximate to 40 degrees C exceeding by 24% that measured at T-a approximate to 10 degrees C. Our data do not support recent arguments that respiratory gas exchange across the wing membranes represents 5%-10% of the total in E. wahlbergi.