Submitted on July 29, 2002
Accepted on March 26, 2003
Validation of the doubly labeled water method under low and high humidity to estimate metabolic rate and water flux in a tropical snake (Boiga irregularis)
Nancy L Anderson1*, Thomas E Hetherington1, and Joseph B Williams1
1 Department of Evolution, Ecology and Organismal Biology, The Ohio State University, Columbus, OH, USA
* To whom correspondence should be addressed. E-mail: nanderson{at}wildlife-museum.org.
This study uses indirect calorimetry to assess the effects of humidity on the accuracy of the doubly labeled water (DLW) technique to predict metabolic rate and water flux in brown treesnakes (Boiga irregularis). The DLW technique accurately predicted total water efflux in brown treesnakes under low humidity conditions and found that the total number of water molecules exchanged with the environment under humid conditions was not significantly different than maximum net total evaporative water loss under low humidity conditions plus fecal water loss. Due to changes of total body water of greater than 12%, the DLW technique over-estimated metabolic rate by a factor of 2.2 under low humidity conditions. Under high humidity conditions, the DLW technique over-estimated metabolic rate in brown treesnakes by a factor of 4.6. Researchers using the DLW technique in humid or moist environments should be cautious because this study indicates that DLW estimates of metabolic rate may be inflated when large amounts of water vapor are exchanged through the skin or respiratory passages.
