Forma, Vol. 20 (No. 1), pp. 19-38, 2005
Original Paper

Analysis and Evaluation for Trajectories of Paramecia

Shuntaro Shinohara1, Toshihiro Akiyama1, Shingo Ishiwata2 and Osamu Hirayama1*

1Graduate School, Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, Koganei-shi, Tokyo 184-8588, Japan
2Department of Physics, Faculty of Engineering, Yokohama National University, Yokohama-shi, Kanagawa 240-8501, Japan
*E-mail address:

(Received February 25, 2005; Accepted December 7, 2005)

Keywords: Paramecium, Trajectory, Localized Direction Change (LDC), Random Walk, Evaluation Function

Abstract. Trajectories of paramecium observed with a microscope were analyzed and it was found that they are composed of four components, namely, Segment, Wavelike form, Arc and Localized Direction Change (LDC). Similar experiments were conducted also in the case that temperature gradient exists and the frequencies of LDC per unit time were measured in both cases. Angle distributions in direction changes and some fitting functions were obtained. It was clarified that the frequency of LDC in the case that the paramecium moves toward the proper temperature area is less than toward improper one. It was confirmed that random walk time scales were nearly equal to the average time interval of LDC. Numerical simulations were conducted and the optimum value for the probability of LDC per unit time which maximize the evaluation function was obtained.

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