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First published online November 5, 2004
Journal of Experimental Biology 207, 4185-4193 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01274

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Infrasound initiates directional fast-start escape responses in juvenile roach Rutilus rutilus

Hans E. Karlsen^1,*, Robert W. Piddington^1,2, Per S. Enger¹ and Olav Sand¹

¹ Institute of Biology, University of Oslo, Blindern N-0316, Norway
² Vision Touch and Hearing Research Centre, School of Biomedical Sciences, University of Queensland 4072, Australia

View larger version (17K): [in a new window]   Fig. 1. Comparison of the waveform of a 4 Hz driving voltage to the vibrator and the resulting acceleration and displacement of the chamber, as well as the pressure changes inside the chamber. The pressure was measured close to the leading and the trailing chamber wall, respectively. The figure reflects relative waveforms only, and all parameters are presented in arbitrary units. The driving waveform comprised a single cycle of a sinusoid that was d.c.-shifted one peak value and phase-shifted to start at –90°. The waveform of the initial acceleration approached a sinusoid of about 1.7 x the driving frequency, whereas the frequency of the initial compression or rarefaction inside the chamber was about 2.1 x the driving frequency.

View larger version (33K): [in a new window]   Fig. 2. Smoothed startle trajectories displayed by juvenile roach in response to the initial half-cycle of an acceleration of about 6.7 Hz, at a stimulus level approximately 15 dB above the response threshold. Movements of the fish where measured in the horizontal plane from video frames recorded by a camera looking down on the fish through the transparent roof of the test chamber. The trajectories show movements of the head of the responding fish during a 160 ms period, i.e. from the video frame before stimulus onset (0,0) and through the subsequent four frames. (A) Trials in push mode with the initial acceleration to the left resulted in 36 startle responses from fish in the trailing (right) half of the chamber, which experienced compression, and no responses from fish exposed to rarefaction in the leading (left) half. (B) Tests in pull mode with the initial acceleration to the right resulted in 35 startle responses from fish in the trailing (left) half of the chamber and 3 startle responses (not illustrated) in the leading (right) half of the chamber. Startle responses in both stimulus situations were on average in the same direction as the initial acceleration.

View larger version (18K): [in a new window]   Fig. 3. Histograms showing the angle between the direction of initial acceleration (0°) and the final escape direction. The presented data were calculated using the last two coordinates of the 71 escape trajectories shown in Fig. 2. A total of 69 final escape angles fell within ±90° of the stimulus direction, and approximated a symmetric and unimodal distribution.

View larger version (19K): [in a new window]   Fig. 4. Histograms presenting the numbers of responsive and non-responsive juvenile roach (2.5 cm) in the rarefaction and compression half of the test chamber, respectively. The frequency of the initial half-cycle of the acceleration was about 6.7 Hz, and the stimulus level was approximately 15 dB above response threshold in all trials. The fish mainly responded to the combination of linear acceleration and a pressure increase. Blocking of the lateral line system by adding 0.1 mmol l–1 Co2+ to the water (Co2+ water) did not significantly change the observed response patterns. The escape responses (see Fig. 2) were therefore triggered by stimulation of the inner ear.

View larger version (29K): [in a new window]   Fig. 5. Smoothed escape trajectories obtained as described in Fig. 2, but from juvenile roach having the lateral line system blocked by 0.1 mmol l–1 Co2+. Eliminating the sensory function of the lateral line organs did not significantly change the response patterns. Response trajectories were still mainly in the direction of the initial acceleration, and 25 of the 26 observed startle responses occurred in the compression (trailing) half of the test chamber. For comparison, the trajectories of fish in normal freshwater, as shown in Fig. 2, are included as dotted lines.