Aerobic Metabolism and Physiological Responses of Aquatic Oligochaetes to Environmental Anoxia: Heat Dissipation, Oxygen Consumption, Feeding, and Defecation

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Abstract
Anoxic heat dissipation of Lumbriculus variegatus, as measured by direct calorimetry, is reduced by up to 85% relative to aerobic rates. The decrease of anoxic heat dissipation and the diminution of activity peaks in the calorimetric output coincide with the disappearance of peristaltic movements under anoxia. A transfer from aerobic conditions with food to anoxia without food results in cessation of defecation when the gut is half emptied, whereas the gut is completely emptied under aerobic conditions within 6 and 8-10 h at 20 and 11 C, respectively. The aerobic retention time of the food is independent of worm length (10-50 mm). After aerobic feeding the gut content is higher than after anoxic feeding at 6 C. On return to aerobic conditions, heat dissipation increases immediately, whereas defecation is resumed only after a lag of 2 h. An anoxic component to the aerobic heat dissipation becomes apparent in relation to simultaneous respirometric measurements when feces accumulate in the calorimetric chamber. When the guts are completely emptied before the experiment, the theoretical oxycaloric equivalent yields an accurate estimate of heat dissipation, indicating that no significant net formation of anoxic end products occurs under aerobic conditions. Anoxic catabolism of glycogen may not fully explain the directly measured rates of heat dissipation under environmental anoxia. This has been suggested earlier for Lumbriculus and has since been confirmed for Tubifex on the basis of simultaneous calorimetric and biochemical measurements. Direct calorimetry is required to assess total rates of metabolic energy expenditure in anoxic oligochaetes.

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