The effect of heat transfer mode on heart rate responses and hysteresis during heating and cooling in the estuarine crocodile Crocodylus porosus

Franklin, Craig E. and Seebacher, Frank (2003) The effect of heat transfer mode on heart rate responses and hysteresis during heating and cooling in the estuarine crocodile Crocodylus porosus. Journal of Experimental Biology, 206 7: 1143-1151. doi:10.1242/jeb.00222

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Author Franklin, Craig E.
Seebacher, Frank
Title The effect of heat transfer mode on heart rate responses and hysteresis during heating and cooling in the estuarine crocodile Crocodylus porosus
Journal name Journal of Experimental Biology   Check publisher's open access policy
ISSN 0022-0949
Publication date 2003-04-01
Year available 2003
Sub-type Article (original research)
DOI 10.1242/jeb.00222
Open Access Status File (Publisher version)
Volume 206
Issue 7
Start page 1143
End page 1151
Total pages 9
Place of publication Cambridge
Publisher Company of Biologists
Language eng
Subject C1
270604 Comparative Physiology
780105 Biological sciences
Abstract The effect of heating and cooling on heart rate in the estuarine crocodile Crocodylus porosus was studied in response to different heat transfer mechanisms and heat loads. Three heating treatments were investigated. C. porosus were: (1) exposed to a radiant heat source under dry conditions; (2) heated via radiant energy while half-submerged in flowing water at 23degreesC and (3) heated via convective transfer by increasing water temperature from 23degreesC to 35degreesC. Cooling was achieved in all treatments by removing the heat source and with C. porosus half-submerged in flowing water at 23degreesC. In all treatments, the heart rate of C. porosus increased markedly in response to heating and decreased rapidly with the removal of the heat source. Heart rate during heating was significantly faster than during cooling at any given body temperature, i.e. there was a significant heart rate hysteresis. There were two identifiable responses to heating and cooling. During the initial stages of applying or removing the heat source, there was a dramatic increase or decrease in heart rate ('rapid response'), respectively, indicating a possible cardiac reflex. This rapid change in heart rate with only a small change or no change in body temperature (<0.5degreesC) resulted in Q(10) values greater than 4000, calling into question the usefulness of this measure on heart rate during the initial stages of heating and cooling. In the later phases of heating and cooling, heart rate changed with body temperature, with Q(10) values of 2-3. The magnitude of the heart rate response differed between treatments, with radiant heating during submergence eliciting the smallest response. The heart rate of C porosus outside of the 'rapid response' periods was found to be a function of the heat load experienced at the animal surface, as well as on the mode of heat transfer. Heart rate increased or decreased rapidly when C porosus experienced large positive (above 25W) or negative (below -15W) heat loads, respectively, in all treatments. For heat loads between -15W and 20W, the increase in heart rate was smaller for the 'unnatural' heating by convection in water compared with either treatment using radiant heating. Our data indicate that changes in heart rate constitute a thermoregulatory mechanism that is modulated in response to the thermal environment occupied by the animal, but that heart rate during heating and cooling is, in part, controlled independently of body temperature.
Keyword Biology
Heart Rate
Heat Transfer
Body Temperature
Crocodylus Porosus
Fresh-water Crocodiles
Lizard Pogona-barbata
Evolutionary Adaptation
Behavioral Thermoregulation
Seasonal Acclimatization
Enzyme Expression
Pineal Complex
Q-Index Code C1
Institutional Status UQ
Additional Notes DOI: 10.1242/jeb.00222

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Created: Wed, 15 Aug 2007, 05:10:08 EST