PT  - JOURNAL ARTICLE
AU  - Overgaard, Johannes
AU  - Andersen, Jonas L.
AU  - Findsen, Anders
AU  - Pedersen, Pil B. M.
AU  - Hansen, Kasper
AU  - Ozolina, Karlina
AU  - Wang, Tobias
TI  - Aerobic scope and cardiovascular oxygen transport is not compromised at high temperatures in the toad <em>Rhinella marina</em>
AID  - 10.1242/jeb.070110
DP  - 2012 Oct 15
TA  - The Journal of Experimental Biology
PG  - 3519--3526
VI  - 215
IP  - 20
4099  - http://jeb.biologists.org/content/215/20/3519.short
4100  - http://jeb.biologists.org/content/215/20/3519.full
SO  - J. Exp. Biol.2012 Oct 15; 215
AB  - Numerous recent studies convincingly correlate the upper thermal tolerance limit of aquatic ectothermic animals to reduced aerobic scope, and ascribe the decline in aerobic scope to failure of the cardiovascular system at high temperatures. In the present study we investigate whether this ‘aerobic scope model’ applies to an air-breathing and semi-terrestrial vertebrate Rhinella marina (formerly Bufo marinus). To quantify aerobic scope, we measured resting and maximal rate of oxygen consumption at temperatures ranging from 10 to 40°C. To include potential effects of acclimation, three groups of toads were acclimated chronically at 20, 25 and 30°C, respectively. The absolute difference between resting and maximal rate of oxygen consumption increased progressively with temperature and there was no significant decrease in aerobic scope, even at temperature immediately below the lethal limit (41–42°C). Haematological and cardiorespiratory variables were measured at rest and immediately after maximal activity at benign (30°C) and critically high (40°C) temperatures. Within this temperature interval, both resting and active heart rate increased, and there was no indication of respiratory failure, judged from high arterial oxygen saturation, PO2 and [HbO2]. With the exception of elevated resting metabolic rate for cold-acclimated toads, we found few differences in the thermal responses between acclimation groups with regard to the cardiometabolic parameters. In conclusion, we found no evidence for temperature-induced cardiorespiratory failure in R. marina, indicating that maintenance of aerobic scope and oxygen transport is unrelated to the upper thermal limit of this air-breathing semi-terrestrial vertebrate. CTmaxmaximum critical temperaturefHheart rate[Hb]haemoglobin concentration[Hb4]tetrameric haemoglobin concentrationHbO2haemoglobin bound oxygenHbO2,sathaemoglobin oxygen saturationHcthaematocritMAPmean arterial pressureMCHCmean cellular haematocrit concentration[O2]aarterial oxygen concentrationPaCO2arterial PCO2PaO2arterial oxygen tensionpHaarterial pHRMRresting metabolic ratemaximum rate of oxygen consumptionαCO2plasma solubility of CO2αO2plasma solubility of O2