ENERGETICS AND WATER FLUX IN A SEMIAQUATIC LIZARD, VARANUS-MERTENSI

Varanus mertensi is a semiaquatic lizard that lives near permanent wat er in northern Australia. During the wet and dry seasons, we measured the field metabolic rate (FMR) and water flux rates of animals in the field and standard metabolic rates across a range of body temperatures (18-96 C) in the laboratory. We combined these data to divide the FMR into energy expended during periods of rest and activity. The FMR was significantly higher in the wet season (120.7 kJ kg(-1) day(-1)) than in the dry season (81.1 kJ kg(-1) day(-1)). There was no difference i n the water flux rate between the wet (63.2 ml kg(-1) day(-1)) and dry (66.5 ml kg(-1) day(-1)) seasons. The FMR during the wet season is gr eater than that predicted for a similarly sized iguanid lizard, but th e 95% confidence interval around the mean FMR in the dry season overla ps the predicted iguanid value. The calculated percent of the FMR devo ted to activity is high for both seasons (70-73%) compared to other li zards, as is the calculated sustainable metabolic scope (3.4-3.7), Whe n compared to terrestrial varanid lizards living in the same area duri ng their active seasons, V. mertensi does not show any quantitative di fferences in FMR or water flux. Varanus mertensi does differ from thes e terrestrial species in not having an inactive period during the dry season, and we suggest that this is related to the continual availabil ity of food and water in its habitat.