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This Article Full Text Full Text (PDF) All Versions of this Article: 288/4/R992    most recent 00593.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (6) Citing Articles via Google Scholar Google Scholar Articles by Clark, T. D. Articles by Frappell, P. B. Search for Related Content PubMed PubMed Citation Articles by Clark, T. D. Articles by Frappell, P. B.

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.