The energetics of Amoeba Proteus Leidy

Abstract

The study dealt with the energetics of the large naked sarcodine, Amoeba proteus, when fed a range of Tetrahymena pyriformis concentrations (125 - 4000 cells 500μl-1) at 10°C, 15°C and 20°C. Part 1 of the thesis was concerned with measuring the individual parameters of the energy budget equation, namely consumption, production and respiration. The dried weights of the predator Amoeba and the prey species Tetrahymena were 0.147pg μm-3 and 0.162pg μm-3 respectively, regardless of temperature. The calorific content of A. proteus was found to be 17.51J mg-1 and was unaffected by temperature; the energy content of T. pyriformis was higher - 19.80J mg-1 at 20°C and 15°C, and 18.28J mg-1 at 10°C. Energy yields were determined by combustion of freeze-dried pellets in a Phillipson micro-bomb calorimeter. The effect of the environmental parameters, temperature and food concentration, on the generation times of A. proteus were investigated. Doubling times ranged from 44 to 84 hours, 71 to 112 hours and 372 to 2,926 hours at 20°C, 15°C and 10°C respectively. The rate of consumption increased with increasing temperature, attained a peak and decreased thereafter. The food level promoting maximum consumption decreased with decreasing temperature. As a consequence of the extended generation times with decreased temperature, consumption per generation was greatest at 10°C. Maxima energy intakes of 92,931μJ, 17,294μj and 8,127μJ were calculated for 10°C, 15°C and 20°C respectively. The volume of protoplasm produced over the cell cycle was the parameter used to measure production. The cell volume doubled over a generation from the daughter cell to the point before fission. The rate of production was influenced by temperature and food concentration and was found to be linear throughout the cell cycle. Increasing temperature increased the rate of production, while increased food supply initially increased the production up to a threshold level, after which the rate decreased. Maximum production was attained at a food concentration of 2000 cells 500μl-1 for 20°C, 1500 cells 500μl-1 for 15°C and 500 cells 500μl-1 for 10°C. Further, decreasing the temperature increased the size of the Amoeba cells; a function of the long generation times at the lower temperatures. Respiration was measured by Cartesian diver microrespirometry. The rate of oxygen consumption per unit volume (μm3) was dependent upon temperature, 5.40 x 10-10μl 02 h-1, 2.61 x 10-10μl 02 h-1 and 2.34 x 10-10μl 02 h-1 at 20°C, 15°C and 10°C respectively. Part 2 of the thesis was concerned with the compilation of a series of both generation and instantaneous energy budgets for individual Amoeba spanning the range of food concentrations and temperatures investigated. The biological efficiencies, linking the parameters of the budget equation, were compared with the relevant published data. Assimilation efficiencies for A. proteus ranged from 22% to 59% regardless of temperature. Net production efficiencies were high — 65% to 82% - at 15°C and 20°C but low at 10°C (11% to 49%). Gross production efficiencies were also higher at 15°C and 20°C (16% to 47%) than at 10°C (4% to 29%). In Part 3, the distribution of A. proteus and related species in the field was discussed, with particular reference to a Sphagnum bog-pool. A tentative annual production estimate, based upon both the field and laboratory experiments, of 49.74kJ m-2 yr-1 (to a depth of 10cm) was calculated. The thesis was concluded with a General discussion in Part 4.