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The heart rate/oxygen consumption relationship during cold exposure of the king penguin: a comparison with that during exercise

G. Froget^1,2, Y. Handrich², Y. Le Maho², J.-L. Rouanet³, A. J. Woakes¹ and P. J. Butler^1,*

¹ School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
² Centre d'Ecologie et Physiologie Energétiques, CNRS, 23 rue Becquerel, 67087 Strasbourg Cedex 02, France
³ Laboratoire de Thermorégulation et Energétique de l'Exercice, CNRS, Faculté de Médecine Lyon-Nord, 69373 Lyon Cedex 08, France

View larger version (22K): [in a new window]   Fig. 1. Diagram of the open-circuit system used to monitor rates of oxygen consumption and carbon dioxide production in king penguins at a variety of ambient temperatures. Ta, ambient temperature; RH, relative humidity.

View larger version (17K): [in a new window]   Fig. 2. Relationship between body temperature (Tb) and ambient temperature (Ta) in nine adult king penguins. The regression line is Tb=0.007Ta+37.5 (r2=0.045, P>0.05, N=92).

View larger version (26K): [in a new window]   Fig. 3. Comparison of data obtained in two different seasons (open circles, 1997-1998; plus signs, 1999-2000). (A) Mass-specific rate of oxygen consumption; (B) heart rate plotted against ambient temperature. Values are means ± S.E.M., N=203. Some error bars are within the size of the symbol.

View larger version (15K): [in a new window]   Fig. 4. Relationship between mass-specific rate of oxygen consumption (sO2, ml min-1 kg-1) and ambient temperature (Ta, °C) in 31 adult king penguins. The regression lines for mass-specific rate of oxygen consumption versus ambient temperature are as follows: above -5 °C, sO2=-0.057Ta+10.32, r2=0.021, P>0.06; below -5 °C, sO2=-0.343Ta+8.93, r2=0.43, P<0.0001. The two regression lines intersect at -4.9 °C, the lower critical temperature (LCT). Values are means ± S.E.M., N=203.

View larger version (20K): [in a new window]   Fig. 5. Rate of oxygen consumption (O2) as a function of heart rate (fH) for 24 adult king penguins walking on a treadmill (grey symbols, the grey line is the regression equation: O2=3.39fH-136.86, r2=0.63, P<0.001; data are from Froget et al., 2001) and for 26 resting adults exposed to different temperatures (open squares, the black line is the regression equation: O2=1.09fH+26.10, r2=0.46, P<0.001).

View larger version (14K): [in a new window]   Fig. 6. Resting oxygen pulse (ROP) of 26 king penguins at a variety of temperatures plotted against the nutritional index (NI, for details, see text). The solid black line is the regression line between ROP and NI for resting penguins at a variety of temperatures (ROP=1.09+0.096NI, r2=0.32, P=0.015), and the thin grey line and the dotted line are the regression lines between NI and the resting oxygen pulse (ROP) above and below the lower critical temperature, respectively. The thick grey line is the ROP obtained in the previous study (Froget et al., 2001).

View larger version (16K): [in a new window]   Fig. 7. Graphic representation of the different equations available to estimate rate of oxygen consumption from heart rate using the equations from Froget et al. (2001) when the animal is resting (solid line) or active (walking on a treadmill, grey line) or using the equation from the present study (broken line). The regression equations are derived from a hypothetical bird with a bill length of 123.8 mm and a body mass of 12.2 kg. The black circles represent the estimated rate of oxygen consumption when the animal is resting on sea water.