VELOCITY AND GRAVIRESPONSES IN PARAMECIUM DURING ADAPTATION AND VARIED OXYGEN CONCENTRATIONS

Populations of Paramecium caudatum adapted to new O2- and chemical env ironments within at least 6 hours show two subgroups of cells which ar e distinguished by their median swimming velocity. ''Fast swimmers'' p revailed at the beginning, and ''normal swimmers'' toward the end of t he adaptation period. The median swimming rate of these two groups was largely constant throughout 6 hours, apart from initial disturbances following transfer into a closed environment. The degree of air satura tion of the experimental solution (5% to 100%) was monitored continuou sly in a new flow-through chamber. Changes in the O2 level did not hav e a consistent effect on the swimming velocity. Negative gravitactic o rientation in normal swimmers gradually decreased with incubation time . Gravitaxis was absent in the fast swimmers. Variation in O2 tension did not produce perceptible effects on gravitaxis. At all air saturati ons and incubation times negative gravikinesis was found, both in norm al and in fast swimmers, centering near -40 mum/s. Gravikinesis correl ated with swimming velocity, but not with O2 tension. No correlation w as found between the kinesis and orientation coefficients. The data su ggest that gravikinesis in Paramecium is largely independent of O2 lev els and adaptation time. Graviorientation declines with adaptation, bu t is not a direct function of O2 saturation of the medium.