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The relationship between heart rate and rate of oxygen consumption in Galapagos marine iguanas (Amblyrhynchus cristatus) at two different temperatures
1 School of Biosciences, The University of Birmingham, Birmingham, B15 2TT,
UK
2 Department of Zoology, La Trobe University, Melbourne, Victoria 3086,
Australia
3 Department of Ecology and Evolutionary Biology, Princeton University,
Princeton, NJ 08544-1003, USA
Present address: Department of Zoophysiology, University of Aarhus,
Universitetsparken, Aarhus 8000C, Denmark
* Author for correspondence (e-mail: p.j.butler{at}bham.ac.uk )
Accepted 9 April 2002
To enable the use of heart rate (fH) for estimating field
metabolic rate (FMR) in free-ranging Galapagos marine iguanas
Amblyrhynchus cristatus, we determined the relationships between
fH and mass-specific rate of oxygen consumption
(s
O2) in seven
iguanas before and during exercise on a treadmill and during the post-exercise
period. The experiments were conducted at 27 and 35°C, which are the
temperatures that represent the lowest and highest average body temperatures
of these animals in the field during summer. There were linear and significant
relationships between fH and
sO2 at both
temperatures (r2=0.86 and 0.91 at 27°C and 36°C,
respectively). The slopes of the two regression lines did not differ, but
there were significant differences in their intercepts. Thus, while heart rate
can be used to predict FMR, the effects of temperature on the intercept of the
regression must be taken into account when converting fH to
sO2. On the
basis of our data, this can be achieved by applying the following formula:
 |
O2 with
elevated body temperature results from an increase in fH, with no
significant change in mass-specific oxygen pulse (sO2 pulse;
cardiac stroke volume times the difference in oxygen content between arterial
and mixed venous blood). However, during exercise at both temperatures,
increases in fH are insufficient to provide all of the additional
O2 required and there are also significant increases in the
sO2 pulses. This creates the situation whereby the same fH
at the two temperatures can represent different values of
sO2.
Key words: heart rate, rate of oxygen consumption, exercise, Galapagos marine iguana, Amblyrhynchus cristatus
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