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SLEEP AND TEMPERATURE REGULATION

Factorial scopes of cardio-metabolic variables remain constant with changes in body temperature in the varanid lizard, Varanus rosenbergi

¹Adaptational and Evolutionary Respiratory Physiology Laboratory, Department of Zoology, La Trobe University, Melbourne, Victoria, Australia; ²Department of Zoophysiology, University of Aarhus, Aarhus, Denmark; and ³School of Biosciences, University of Birmingham, Birmingham, United Kingdom

Submitted 30 August 2004 ; accepted in final form 25 November 2004

The majority of information concerning the cardio-metabolic performance of varanids during exercise is limited to a few species at their preferred body temperature (T_b) even though, being ectotherms, varanids naturally experience rather large changes in T_b. Although it is well established that absolute aerobic scope declines with decreasing T_b, it is not known whether changes in cardiac output (_b) and/or tissue oxygen extraction, (Ca_O2 – C), are in proportion to the rate of oxygen consumption (O₂). To test this, we studied six Rosenberg's goannas (Varanus rosenbergi) while at rest and while maximally exercising on a treadmill both at 25 and 36°C. During maximum exercise both at 25 and 36°C, mass-specific rate of oxygen consumption (O_2kg) increased with an absolute scope of 8.5 ml min^–1 kg^–1 and 15.7 ml min^–1 kg^–1, respectively. Interestingly, the factorial aerobic scope was temperature-independent and remained at 7.0 which, at each T_b, was primarily the result of an increase in _bkg, governed by approximate twofold increases both in heart rate (f_H) and cardiac stroke volume (V_Skg). Both at 25°C and 36°C, the increase in _bkg alone was not sufficient to provide all of the additional oxygen required to attain maximal O_2kg, as indicated by a decrease in the blood convection requirement _bkg/O_2kg; hence, there was a compensatory twofold increase in (Ca_O2 – ). Although associated with an increase in hemoglobin-oxygen affinity, a decrease in T_b did not impair unloading of oxygen at the tissues and act to reduce (Ca_O2 – C); both Ca_O2 and C were maintained across T_b. The change in O_2kg with T_b, therefore, is solely reliant on the thermal dependence of _bkg. Maintaining a high factorial aerobic scope across a range of T_b confers an advantage in that cooler animals can achieve higher absolute aerobic scopes and presumably improved aerobic performance than would otherwise be achievable.

metabolic rate; Fick equation; exercise; cardiac output; oxygen consumption; heart rate; stroke volume; reptile; goanna; oxygen extraction.

This article has been cited by other articles:

				T.D Clark, B.D Taylor, R.S Seymour, D Ellis, J Buchanan, Q.P Fitzgibbon, and P.B Frappell Moving with the beat: heart rate and visceral temperature of free-swimming and feeding bluefin tuna Proc R Soc B, December 22, 2008; 275(1653): 2841 - 2850. [Abstract] [Full Text] [PDF]