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
Infrasound initiates directional fast-start escape responses in juvenile roach Rutilus rutilus
Hans E. Karlsen1,*,
Robert W. Piddington1,2,
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
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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.
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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.
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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.
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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.
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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.
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© The Company of Biologists Ltd 2004
