Corn& Biochem. Phyriol., 1974, Vol. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLK 49A, pp. 583 to 601. Pergmmm Press. Printed in Great Britain METABOLIC SCOPE, OXYGEN DEBT AND THE DIURNAL OXYGEN CONSUMPTION CYCLE OF THE LEOPARD FROG, zyxwvutsrqponmlkjihgfedcbaZYXWVUTS RANA PIPIENS zyxwvutsrqponmlkjihg L. DOUGLAS TURNEY and VICTOR H. HUTCHISON Department of Zoology, University of Oklahoma, Norman, Oklahoma 73069, U.S.A. (Receiwed 29 August 1973) zyxwvutsrqponmlkjihgfedcbaZYXW Abstract-l. Oxygen consumption was measured with an automatic con- stantly recording electrolysis apparatus in leopard frogs (Rum pipiens) accli- mated at 15 and 25°C. All groups acclimated under a photoperiod of LD12 : 12 exhibited a distinct diurnal metabolic minimum during the first hour after the onset of the photophase and a significant metabolic maximum rate during the first hour after the onset of the scotophase. 2. Studies of animals conducted under constant light (LL) and darkness (DD) showed a mid-day metabolic maximum cycle with no pronounced metabolic minimum. 3. Aerobic metabolic scope produced by Faradic stimulation for 30-min periods was thermally dependent and varied with the time of the daily cycle of the shocking process. At 15”C, the mean oxygen consumption above routine metabolism (21.0 ~1 g-l hr-‘) was significantly lower than the absolute scope at 25°C (36.0 ~1 g-l hr-*). 4. Oxygen debt increased with temperature and varied with the time of day the animals were shocked. Mean oxygen debt at 25°C was 80.7 ~1 Or g-l, 42 per cent higher than at 15°C (56.7 ~10, g-l). Conversion of oxygen debt to lactate yielded corresponding values of 0.98 (15’C) and 140 mg g-l (25°C). Recovery periods for oxygen debts averaged 3.7 hr. 5. The total energetic expenditures during periods of maximal activity above the routine metabolic level were 0.37 cal g-l at 15°C and 0.55 cal g-l at 25°C. Of the energy expended above the routine metabolic rate during strenuous activity, 69 and 73 per cent were supported anaerobically at 25 and lS”C, respectively. INTRODUCTION ONE OF the most useful concepts for the student of animal energetics concerned with understanding metabolism in a reasonable realistic ecological context is that of metabolic scope for activity (Bartholomew, 1968). Fry (1947), working with fish, defined metabolic scope as the difference between minimum (basal or standard metabolic rate) and maximum rates of metabolism under given conditions. This concept is similar to the index of metabolic expansibility (i.e. the ratio of maximal to minimal metabolism) defined by Drabkin (1959). The terminology of animal energetics with respect to metabolic rates and corresponding states of activity is 583