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First published online August 17, 2006
Journal of Experimental Biology 209, 3405-3412 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02421

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Development of swimming behaviour in the larva of the ascidian Ciona intestinalis

Giuliana Zega^1,2,*, Michael C. Thorndyke² and Euan R. Brown¹

¹ Neurobiology Laboratory Stazione Zoologica `Anton Dohrn', Villa Comunale I-80121 Naples, Italy
² Royal Swedish Academy of Sciences Kristineberg Marine Research Station, SE-45034 Fiskebäckskil, Sweden

^* Author for correspondence at present address: Dipartimento di Biologia `L. Gorini', Università degli Studi di Milano, Via Celoria 26, I-20133 Milano, Italy (e-mail: giuliana.zega{at}unimi.it)

Accepted 1 July 2006

The aim of this study was to characterize the swimming behaviour of C. intestinalis larvae during the first 6 h after hatching by measuring tail muscle field potentials. This recording method allowed a quantitative description of the responses of the larva under light and dark conditions. Three different larval movements were distinguished by their specific frequencies: tail flicks, `spontaneous' swimming, and shadow response, or dark induced activity, with respective mean frequencies of about 10, 22 and 32 Hz. The shadow response develops at about 1.5 h post hatching (h.p.h.). The frequency of muscle potentials associated with this behaviour became higher than those of spontaneous swimming activity, shifting from 20 to 30 Hz, but only from about 2 h.p.h. onwards. Swimming rate was influenced positively for about 25 s after the beginning of the shadow response. Comparison of swimming activity at three different larval ages (0-2, 2-4 and 4-6 h.p.h.) showed that Ciona larvae swim for longer periods and more frequently during the first hours after hatching. Our results provide a starting point for future studies that aim to characterize the nervous control of ascidian locomotion, in wild-type or mutant larvae.

Key words: shadow response, electrophysiology, muscle field potentials, nervous system, locomotion, Ciona intestinalis