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 (Ta) from 10° to 40°C. The bats' normothermic body temperature (Tb) was approximately 36°C, which increased at higher Ta to 40.5° ± 1.0°C at Ta ≈ 40°C. Both TEWL and resting metabolic rate (RMR) increased sharply at Ta >35°C, with a mean TEWL at 40°C equivalent to 411% of that at 30°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 Ta range, with the exception of Ta ≈ 40°C, where REWL accounted for 58% of evaporative water loss. Surface area-specific CEWL increased approximately sixfold with increasing Ta. Thermoregulation at Ta approaching or exceeding Tb involved a considerable energetic cost, with RMR at Ta ≈ 40°C exceeding by 24% that measured at Ta ≈ 10°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.
Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa; 2South African Research Chair for Mammal Behavioural Ecology and Physiology, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield, 0028 South Africa.
Ingrid A
IA
Minnaar
Nigel C
NC
Bennett
Christian T
CT
Chimimba
Andrew E
AE
McKechnie
D000818:Animals; D001481:Basal Metabolism; D001831:Body Temperature; D002685:Chiroptera / Q000502:physiology*; D006358:Hot Temperature; D012119:Respiration; D012879:Skin Physiological Phenomena; D014867:Water / Q000378:metabolism; D014870:Water Loss, Insensible / Q000502:physiology*; D014921:Wings, Animal / Q000502:physiology
D014867:Water