AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 5 1325-R1328, Copyright © 1991 by American Physiological Society
Oxidative cost of breathing in the turtle Chrysemys picta bellii
D. C. Jackson, J. H. Singer and P. T. Downey
Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912.
We estimated the cost of breathing of turtles by measuring ventilation and
oxygen consumption during air breathing and CO2 breathing. We assumed that
any increment in oxygen consumption due to hypercapnic hyperpnea was due to
the metabolic cost of the increased breathing. Six turtles were studied
while breathing air and then 5% CO2 in air after at least 12 h breathing
each gas. For the measurements, the turtles were submerged unrestrained in
water at 20 degrees C and were free to raise their heads into a ventilated
chamber. Tidal volumes were measured by the pressure changes in the
chamber, and oxygen consumption was measured by conventional open-circuit
respirometry. Ventilation increased markedly during CO2 breathing up to 50
times the control level, but oxygen consumption increased only slightly.
Assuming no depression in nonventilatory metabolism, our data indicate an
oxidative cost of breathing on the order of 1% of the total metabolic rate
at rest. This is far less than the 15-20% cost predicted from published
work (Kinney et al., Respir. Physiol. 31: 327-332, 1976) on a closely
related species of turtle and is consistent with earlier work in our
laboratory. We conclude that the cost of breathing in turtles is low,
similar to other air-breathing vertebrates, and therefore the existing
notion that turtle breathing is expensive and inefficient should be
discarded.
