BEHAVIORAL RESPONSES IN Paramecium multimicronucleatum TO VISIBLE LIGHT

Specimens of colorless Paramecium multimicronucleatum were found to respond to visible light. They accumulated in the shaded region (photodispersal) of a half-shaded glass tube during 2 min exposure to visible light. The specimens showed avoiding reaction upon both spatial and temporal increase in light intensity (step-up photophobic response). Steady-state swimming velocity (orthokinesis) was higher, while steady-state frequency of spontaneous change in swimming direction (klinokinesis) was lower when the light intensity was kept higher. In a light with wavelength of 440 nm the velocity was highest, while the frequency was lowest. The specimens did not show phototaxis (light direction-oriented locomotion). Spectral sensitivity curves for both the photodispersal and the step-up photophobic response showed a major peak at 520 nm and a minor peak at 680 nm. The photodispersal seems to be caused mainly by the step-up photophobic response exhibited by the specimens at the dark-light border. The photokinetic responses enhance the degree of the photodispersal.