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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 Zega1,2,*, 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


Figure 1
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  		Fig. 1. (A) Swimming larva of Ciona intestinalis. In the trunk the two pigmented organs are visible within the sensory vesicle. Scale bar, 100 µm. (B) Diagram of motor neurons of the visceral ganglion and of the innervation pattern of muscle cells in the tail, dorsal view (modified from Bone, 1992Go; Cole and Meinertzhagen, 2004Go; Brown et al., 2005Go). Neurites connecting motor neurons to the muscle cells in the tail present some varicosities (arrow). ap, adhesive papillae; mc, muscle cell; mn, motor neurons; ne, neurites; N, neck; NT, neural tube; oc, ocellus; ot, otolith; SV, sensory vesicle; tr, trunk; t, tail; VG, visceral ganglion).

 

Figure 2
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  		Fig. 2. Muscle field potential recordings, instantaneous frequencies and mean frequencies. (A) Examples of larval activity at different ages (h.p.h.). Solid bars indicate dark periods (of 5 s). (B) Plots of instantaneous frequency of tail contractions (Hz) vs time (s) from the traces shown in A. Every tail contraction is represented by one dot in the chart. Solid bars under plots and traces indicate the 5s dark period, imposed by the automatic shutter. There was an exact correspondence between the beginning of the light off-period and the beginning of swimming activity. Series of tail flicks, with a mean frequency of about 10 Hz, can be seen to precede or follow swimming bursts. Tail flicks are of larger amplitude than the potentials during swimming periods. Tail flicks can also be seen at the beginning of the shadow response that developed at 1.5 h.p.h. The frequency of potentials during the shadow response increased during larval aging and from 2 h.p.h. it was always higher than spontaneous swimming frequency. The 3.5 h.p.h. plot is also an example of how an active larva could change frequency of swimming if stimulated by a step-down in light. tf, tail ficks; ss, spontaneous swimming; sr, shadow response. (C) Mean frequency of muscle field potentials generated by tail flicks, spontaneous swimming and shadow response at different larval ages (h.p.h.). Frequency values (Hz) are means ± s.d.. Open triangles, tail flicks; grey circles, spontaneous swimming; black circles, shadow response.

 

Figure 3
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  		Fig. 3. Larval distribution pattern photographed from above. (A) Larvae are grouped in a swarm when the light was on. (B) 5 s after the shading the swarm was dispersed. (C) 30 s after the shading, larvae were still swimming in different directions. (D) After 1 min larvae tended to group again.

 

Figure 4
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  		Fig. 4. After-effect of the shadow response. Time 0 s represents the beginning of the shadow response: all frequency values of swimming activity during the dark period are shown with respect to this time. The regression line shows the negative trend of the frequency of muscle field potentials vs time.

 

Figure 5
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  		Fig. 5. Mean duration of bursts of spontaneous swimming during three different post-hatching periods. Data are means ± s.d. For statistical significance, see Results. *P≤0.0001.

 

Figure 6
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  		Fig. 6. Mean total activity per sweep for three different post-hatching periods. Grey columns: without light-off stimulation; black columns: with light-off stimulation. Data are the mean (± s.d.) totals of activity per sweep (s). For the analysis of interaction between larval age and presence or absence of light-off stimulation, see Results.

 

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© The Company of Biologists Ltd 2006