Locomotion without lungs: energetics and performance of a lungless salamander

Lungless salamanders (4.1 g) were exercised on a treadmill enclosed in a Plexiglas respirometer at a range of speeds (0.05-0.24 km/h). O2 consumption (VO2) was determined continuously by open-flow respirometry. At the onset of exercise VO2 increased to a "steady state" in approximately 2-5 min. VO2 (ml O2 X g-1 X h-1) increased linearly with speed (S), VO2 = 2.3 (S) + 0.1 (r2 = 0.74). The minimum cost of transport (2.3 ml O2 X g-1 X km-1) was three-fourths of that predicted for a vertebrate of the same mass. Maximum O2 consumption (VO2max) was attained at 0.16 km/h (maximum aerobic speed), where this VO2 was six to nine times above standard rates. The net rate of whole-body lactate production (WBL) was insignificant at slow speeds (less than 46% VO2max) but did increase at submaximal work loads (85% VO2max). The highest WBL (0.07 mg X g-1 X min-1) was measured at a speed (0.20 km/h) that exceeded the maximum aerobic speed. Salamanders sustained exercise at slow speeds for over 2 h. The greatest decline in endurance (i.e., from 120 to 10 min) occurred at speeds below the maximum aerobic speed, where being lungless may have little consequence. At fast rates of locomotion a limited VO2max was associated with a low maximum aerobic speed and a modest capacity for sustained activity.