SEASONAL METABOLISM OF A SMALL, ARBOREAL MONITOR LIZARD, VARANUS-SCALARIS, IN TROPICAL AUSTRALIA

The field metabolic rates (FMR) and water fluxes of Varanus scalaris w ere measured during the wet and dry seasons by the doubly-labelled wat er technique. Seasonal measurements of standard (night-time) metabolis m (SMR) and resting (daytime) metabolism (RMR) were made in the labora tory at 18, 24, 30 and 36 degrees C, and maximal oxygen consumption wa s measured at 36 degrees C on a motorized treadmill. This population w as active throughout the year. In the wet season, the mean FMR was 7.8 kJ day(-1) (128.0 kJ kg(-1) day(-1); mean mass = 66.4 g, n = 13), and during the dry season the mean was 5.0 kJ day(-1) (67.6 kJ kg(-1) day (-1); mean mass = 77.4 g, n = 17). The mean water flux rates for these animals were 3.6 and 1.2 ml day(-1), respectively (60.4 and 16.6 ml k g(-1) day(-1)). The seasonal means of FMR and water flux were signific antly different by ANCOVA (P < 0.0001). Measurements of SMR and RMR we re significantly higher in the wet season (ANCOVA: P < 0.0001), but we found no difference in the maximal oxygen consumption between seasons (ANCOVA: P = 0.6). The maximal oxygen consumption of the lizards on t he treadmill (2.9 ml min(-1) = 1.8 ml g(-1) h(-1)), mean mass = 97.4 g , n = 16) was 20 times that of the SMR at the same temperature during the dry season, and 11 times that of the SMR during the wet season. Th e seasonal differences in FMR were attributable to: changes in SMR (12 .2%) and RMR (16.4%); differences in night-time body temperatures (11. 3) and daytime body temperatures (16.4%); and activity (broadly define d to include locomotion, digestion, and reproductive costs (43.7%).