Ventilation and Oxygen Consumption in Agamid Lizards

Abstract

To gain a better understanding of the possible effects ventilatory pauses may have on ventilatory requirement (V̇e/V̇o2) in lizards, ventilation (V̇e) and oxygen consumption (V̇o2) together with breathing pattern were examined in a single family of lizards, the Agamidae. Interrelationships between variables were revealed using allometry and the principle of similarity. The results are compared to already-published values for mammals and birds. It appears that in birds, mammals, and lizards (reptiles) overall ventilation and oxygen consumption are perfectly matched and for any group V̇e/V̇o2 is independent of mass. Generally speaking, in all groups, ventilation and oxygen consumption scale to M0.75. However, birds and mammals achieve a 0.75 exponent for ventilation by scaling tidal volume to M1.0 and breathing frequency to M−0.25. Lizards, on the other hand, scale tidal volume to M0.75 and overall breathing frequency to M0.0. Despite these differences all groups would appear to match pump volume (lung) with stroke volume (tidal volume). Additionally, reptiles reduce V̇e/V̇o2 with increasing temperature. Besides having a possible role in regulating blood acid-base balance, such a decrease could result from a limit to O₂ supply. Furthermore, reptiles are discontinuous breathers and appear to regulate overall breathing frequency at different temperatures by altering the periods of nonventilation. At least in the agamids it appears that the time spent in nonventilation is inversely related to mass. This results in an inverse trend between the breathing frequency observed during periods of ventilation (optimal breathing frequency) and mass. In turn, this has the effect of increasing ventilation proportionally more in smaller lizards. An outcome of this is that V̇e/V̇o2 is no longer mass-independent during periods of ventilation. A possible energetic reason for such a relationship is suggested.