Gas exchange and ventilation during dormancy in the tegu lizard Tupinambis merianae

摘要

The tegu lizard Tupinambis merianae exhibits an episodic ventilatory pattern when dormant at 17 deg C but a uniform ventilatory pattern when dormant at 25 deg C. At 17 deg C, ventilatory episodes were composed of 1-22 breaths interspaeed by non-ventilatory periods lasting 1.8-26 min. Dormancy at the higher body temperature was accompanied by higher rates of O_2 consumption and ventilation. The increase in ventilation was due only to increases in breathing frequency with no change observed in tidal volume. The air convection equirement for O_2 did not differ at the two body temperatures. The respiratory quotient was 0.8 at 17 deg C and 1.0 at 25 deg C. We found no consistent relationship between expired gas composition and the start/end of the ventilatory period during episodic breathing at 17 deg C. However, following non-ventilatory periods of increasing duration, there was an increase in the pulmonary O_2 extraction that was not coupled to an equivalent increase in elimination of CO_2 from the lungs. None of the changes in the variables studied could alone explain the initiation/termination of episodic ventilation in the tegus, suggesting that breathing episodes are shaped by a complex interaction between many variables. The estimated oxidative cost of breathing in dormant tegus at 17 deg C was equivalent to 52.3% of the total metabolic rate, indicating that breathing is the most costly activity during dormancy.