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First published online June 6, 2005
Journal of Experimental Biology 208, 2269-2276 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01657

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Digestive state influences the heart rate hysteresis and rates of heat exchange in the varanid lizard Varanus rosenbergi

T. D. Clark^1,*, P. J. Butler² and P. B. Frappell¹

¹ Adaptational and Evolutionary Respiratory Physiology Laboratory, Department of Zoology, La Trobe University, Melbourne, Victoria 3086, Australia
² School of Biosciences, University of Birmingham, Birmingham B15 2TT, UK

View larger version (20K): [in a new window]   Fig. 1. Representative trace of (A) the rate of oxygen consumption (O2), (B) heart rate (fH) and (C) body temperature (Tb) measured from a single individual while fasting (black symbols and lines) and while postprandial (grey symbols and lines). Each trace includes the entire period for which the animal was instrumented, and traces for each digestive state have been aligned to coincide with the period when the lizard moved under the heat lamp. Lizard was fed at 0 h. In C, # and + indicate the times at which the heat lamp was switched on and off, respectively. During the postprandial state, the animal remained at an ambient temperature of 30°C until approximately 23 h, after which room temperature was decreased to 14°C (indicated by hatched vertical line).

View larger version (25K): [in a new window]   Fig. 2. The changes in (A) the rate of oxygen consumption (O2), (B) heart rate (fH) and (C) body temperature (Tb) for V. rosenbergi at an ambient temperature of 30°C measured every hour between 6 h and 23 h following consumption of a meal (10% of fasted body mass; see Materials and methods). All parameters were significantly higher at 23 h postprandial than they were at 6 h postprandial (P<0.05; see Results). The hatched vertical bar indicates the time at which room temperature was decreased to 14°C in order to begin the hysteresis experiments. Values are means ± S.E.M.

View larger version (32K): [in a new window]   Fig. 3. Relationship for V. rosenbergi of (A) the rate of oxygen consumption (O2) and (B) heart rate (fH) versus body temperature (Tb±0.4°C) during heating and cooling in fasting (squares) and postprandial (circles) lizards. Irrespective of digestive state, a hysteresis in O2 during heating and cooling was not observed, although, both during heating and cooling between 25°C and 35°C, O2 was significantly higher in postprandial lizards than in fasting lizards. There was a significant hysteresis in fH during heating and cooling from 19°C to 35°C in fasting animals although, for postprandial animals, the fH hysteresis was significant only between 24°C and 35°C. Values are means ± S.E.M. (C) The absolute differences in fH between heating and cooling for fasting (grey bars) and postprandial (black bars) animals.