Individual variation in physiological traits may have important consequences for offspring survivorship and adult fitness. Variance in offspring phenotypes is due to interindividual differences in genotype, environment, and/or maternal effects. This study examined the contributions of incubation environment, maternal effects, and clutch identity to individual variation in metabolic rates in the common snapping turtle, Chelydra serpentina. We measured standard metabolic rate, as determined by oxygen consumption, for 246 individuals representing 24 clutches at 15 degrees and 25 degrees C, and we measured standard metabolic rates additionally for 34 individuals at 20 degrees and 30 degrees C. Standard metabolic rate for 34 snapping turtles measured at 15 degrees, 20 degrees, 25 degrees, and 30 degrees C increased with increasing temperature. Mean standard metabolic rate for 246 individuals was 0.247 microL O(2) min(-1) g(-1) at 15 degrees C and 0.919 microL O(2) min(-1) g(-1) at 25 degrees C. At 15 degrees C, mass at hatching, individual mass, and egg mass had no significant effects on metabolic rate, but at 25 degrees C, mass at hatching, individual mass, and egg mass did have significant effects on metabolic rate. Incubation temperature had no significant effect on metabolic rate at 15 degrees, but it did have a significant effect at 25 degrees C. Clutch identity had a significant effect on metabolic rate at both 15 degrees and 25 degrees C. Interindividual variation in standard metabolic rate due to incubation temperature, and especially clutch identity, could have large effects on energy budgets. Results suggest that there were both environmental and genetic effects on standard metabolic rate.