VENTILATION AND GAS-EXCHANGE IN LIZARDS DURING TREADMILL EXERCISE

The extent to which lizards ventilate their lungs during locomotion is controversial, Direct measurements of airflow across the nostrils sug gest a progressive reduction in tidal volume and minute ventilation wi th increased running speed, while other studies have demonstrated that arterial P-O2 remains constant during exercise, To resolve these conf licting findings, we measured minute ventilation and gas exchange rate in five specimens of Varanus exanthematicus and five specimens of Igu ana iguana during treadmill locomotion at speeds between 0.14 and 1.11 m s(-1) at 35 degrees C. These speeds are much lower than maximal run ning speeds, but are greater than the maximal aerobic speed, In both s pecies, the ventilatory pattern during locomotion was highly irregular , indicating an interference between locomotion and lung ventilation, In Varanus exanthematicus, treadmill locomotion elicited a six-to eigh tfold increase in minute ventilation from a pre-exercise level of 102 ml kg(-1) min(-1), whereas the rate of oxygen uptake increased approxi mately threefold (from 3.9 to 12.6 ml kg(-1) min(-1)), After exercise, both minute ventilation and gas exchange rate decreased immediately, Because minute ventilation increased more than did oxygen consumption, an increase in lung P-O2 during exercise is predicted and, thus, Vara nus exanthematicus appears effectively to ventilate its lungs to match the increased metabolic rate during locomotion at moderate speed, In Iguana iguana, both minute ventilation and gas exchange rate increased above resting values during locomotion at 0.28 m s(-1), but both decr eased with further increases in locomotor speed, Furthermore, followin g exercise, both minute ventilation and oxygen uptake rate increased s ignificantly, Iguana iguana, therefore, appears to be unable to match the increased oxygen demand with adequate ventilation at moderate and higher speeds.