Food Consumption of the Free-Living Aquatic Nematode Pelodera chitwoodi

Abstract

A Cartesian diver respirometer was used to measure O[sub2] uptake and respiratory quotients at 25 C. Respiratory quotients were about 0.70 in starved nematodes, and 0.80 in third-stage and adult nematodes that had fed on bacteria. The energy output as measured by O[sub2] uptake was inversely related to the concentration of bacteria in the medium, indicating reduction in feeding effort. Feeding bacteria to third-stage nematodes in divers quickly resulted in peak respiration rates averaging 6.4 nl O[sub2]/[mu]g wet weight nematode per hour (QO[sub2]) or six times the endogenous rate. In about 4 hr, the rates fell and then stabilized at a QO[sub2] of 2.5. Adult males fed bacteria in divers had a peak QO[sub2] of 2.8 or twice the starved rate. Adult females fed bacteria had a peak QO[sub2] of 3.7. Starving adult males and third-stage larvae were estimated to lose 2.4% and 1.4%, respectively, of their body weight per day in the form of fat based on the caloric equivalent o f oxygen used and a respiratory quotient of 0.70. The caloric content of the bacteria fed to nematodes in divers was determined. It was then calculated that both third-stage larvae and adult males ingested bacteria equivalent to 4.4 × 10[sup-][sup5] cal/[mu]g wet weight nematode tissue per hour when feeding. Of the bacterial calories ingested, the larvae used 27% and adults 21% for respiration. It was estimated that males ingested 3.1 × 10[sup6] bacteria and females 10 × 10[sup6] bacteria during an 8-day life span. Key Words: respiration, calorimetry, Cartesian diver.