BEHAVIORAL RESPONSES IN Paramecium multimicronucleatum TO VISIBLE LIGHT

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Abstract
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.

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