Activity Metabolism in the Mudpuppy, Necturus maculosus

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Abstract
The mudpuppy, Necturus maculosus, exhibited significant daily cycles of resting oxygen consumption and spontaneous locomotor activity at 5 C and 15 C with an LD 12:12 photoperiod. Resting whole body lactate levels did not vary with time of day at either acclimation temperature, therefore high levels of spontaneous locomotor activity are supported entirely aerobically. Lung breathing accounted for half of the oxygen consumed during periods of high resting oxygen consumption and high spontaneous activity at both acclimation temperatures. When mudpuppies were stimulated for 30 min to complete exhaustion during periods of high resting oxygen consumption, no further increase in oxygen consumption was observed. When mudpuppies were stimulated during a period of low resting oxygen consumption, an increase in oxygen consumption attributable entirely to air breathing was observed. Whole body lactate levels increased during stimulation independent of the time of day of stimulation and apparently independent of acclimation temperature. Mudpuppies did not exhibit an oxygen debt, but rather gradually reduced poststimulation whole body lactate levels over a recovery period of 24 h. The prolonged removal of lactate with no accompanying oxygen debt results in a considerable energy savings for this species. The major source of glucose for anaerobic energy production during exhausting activity is liver glycogen. The strong dependence on anaerobiosis for energy production over resting levels coupled with a prolonged recovery period significantly reduces the energetic cost of activity in Necturus and is further evidence for the "low energy evolutionary strategy" of salamanders.