An investigation of the factors influencing mean cell volume in populations of the ciliate Colpidium campylum

Variation in mean cell volume of the ciliate Colpidium campylum Stokes is described in relation to energy consumption, temperature and population density. Mean cell volume was unaffected by temperature and population density, while energy consumption had a marked effect. A linear relationship existed between mean cell volume and energy consumption up to an energy intake of 8000 μJ during 24 h by each individual present at the beginning of each experiment, above this level of energy intake mean cell volume maintained a maximum. Within the temperature range 10°C‐20°C, temperature had no effect on the mean cell size of C. campylum. Population density also exerted no noticeable effect on mean cell volume. The quantity of energy consumed, however, had a marked effect. In experiments where less than 8000 μJ were consumed/individual/24 h, the mean cell volume decreased. Above this level of energy consumption mean cell volume maintained a constant level. The maximum values obtained for cell sizes were 160–190 × 103μm3 and the minimum values 40–100 × 103μm3. A response to decreased food concentration and hence decreased energy consumption was obtained within the 24 h experimental period, indicating a rapid response to changed environment by the ciliates. Copyright © 1975, Wiley Blackwell. All rights reserved