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Journal of Experimental Biology 137,141-156 (1988)
Published by Company of Biologists 1988

Negative Geotaxis in Sea Urchin Larvae: A Possible Role of Mechanoreception in the Late Stages of Development

Yoshihiro Mogami ¹, Chieko Oobayashi ², Tomoko Yamaguchi ³, Yumi Ogiso ⁴, and Shoji A. Baba ¹

¹ Department of Biology, Ochanomizu University, Otsuka 2-1-1, Tokyo 112, Japan
² Department of Biology, Ochanomizu University, Otsuka 2-1-1, Tokyo 112, Japan: Dinabot, Matsudo, Chiba.
³ Department of Biology, Ochanomizu University, Otsuka 2-1-1, Tokyo 112, Japan: Mitsubishi Chemical Industries, Research Center, Yokohama, Kanagawa.
⁴ Department of Biology, Ochanomizu University, Otsuka 2-1-1, Tokyo 112, Japan: Denenchofu Futaba Gakuen, Setagaya, Tokyo.

Negative geotactic behaviour of sea urchin larvae at various developmental stages from blastula to pluteus was analysed by means of time-exposure dark-field photography of the swimming behaviour of individual larvae. Significant differences in the patterns of behaviour, such as swimming direction and speed, were demonstrated between the early stages (up to the gastrula) and the pluteus, although larvae at any developmental stage showed negative geotactic migration. Larvae in the early stages swam at speeds that varied as a function of the swimming direction with respect to gravity, faster downwards and slower upwards. This might be predicted from the assumption that vertical locomotion is determined by constant propulsion affected passively by gravity. In the pluteus stage, however, larvae swam at a constant speed in any direction, suggesting that the propulsive activity of swimming plutei is actively controlled depending on the swimming direction. This change in the negative geotactic behaviour of sea urchin larvae in the course of embryogenesis indicates development of physiological control systems for propulsive activity at the pluteus stage.

Key words: geotaxis, sea urchin, larvae.

Accepted on January 25, 1988

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