Temperature effects on ventilation and metabolism in the lizard, Ctenophorus nuchalis

Abstract

The effect of temperature upon ventilation and metabolism was measured on a breath by breath basis in the lizard Ctenophorus nuchalis. This species displayed a typical reptilian breathing pattern; groups of breaths separated by periods of breath holding. The lengths of the non-ventilatory periods (NVP) decreased as temperature increased. As a result, overall breathing frequency (f) displayed a thermal dependence. Outside the preferred temperature range (27–37°C) f was also affected by changes in the frequency of breathing that occurred during periods of ventilation (f′). On the other hand, tidal volume (V t) was maintained constant at all temperatures except 42°C (‘panting’ threshold). Thus, due to the thermal dependency off, ventilation (V̇ e) displayed a significant increase between 18 and 37°C. Metabolism (V̇ O 2 and V̇ CO 2 ) also increased within this temperature range. However, as a result of a lower Q 10 for ventilation, ventilatory requirement (V̇ e/V̇ O 2 and V̇ e/V̇ CO 2 ) decreased. In addition, lung volume (LV) increased with temperature. Examination of the alveolar ventilation-P CO 2 relationship revealed that as a result of the increase in LV the level of intrapulmonary CO 2 at the end of an NVP was maintained irrespective of temperature. This implies a temperature-independent chemical threshold for the onset of breathing. It is postulated that with temperature the observed increase in LV could offset the increase in metabolism by slowing the rise of intrapulmonary CO 2 levels. This would delay the onset of breathing which in turn would lower V̇ e/V̇ CO 2 (and V̇ e/V̇ 2 ) by preventing an effectual hyperventilation. This supports the notion, at least in C. nuchalis, that relative alkalinity is maintained.