To ascertain whether the presence of lungs per se, or some other physiological feature, might account for the differences in oxygen consumption and stamina previously observed in an interspecific comparison (Full et al. 1988), individual salamanders (Ambystoma tigrinum) were exercised on a treadmill before and after their nares and mouth had been sealed. After airway closure, animals behaved normally and suffered no mortality. Airway closure reduced the routine MO2 (rate of oxygen consumption) by an average of 47% in six of seven individuals. Animals with open airways increased their MO2 2-to 4-fold during locomotion at 11 cm s−1, and did not fatigue in 22 min of exercise at this speed. Animals with closed airways managed only small increases above the routine MO2 during exercise at 11 cm s−1, and none could sustain activity for more than 10 min. Thus, exclusively skin-breathing Ambystoma cannot increase cutaneous gas exchange to compensate for the elimination of pulmonary and buccopharyngeal respiration; locomotor stamina suffers accordingly. Small salamanders can apparently increase cutaneous gas exchange during activity, although large salamanders cannot, because cutaneous diffusing capacity and the resting oxygen requirement approach one another with increasing body size; the skin of large salamanders apparently has a limited scope for aerobic activity.

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