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First published online May 24, 2004
Journal of Experimental Biology 207, 2339-2349 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01015

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Escape manoeuvres in the spiny dogfish (Squalus acanthias)

Paolo Domenici^1,*, Emily M. Standen² and Robert P. Levine³

¹ CNR-IAMC, c/o International Marine Centre, Loc. Sa Mardini, 09072 Torregrande, Oristano, Italy
² Department of Forestry, University of British Columbia, Vancouver, British Columbia, Canada
³ Organismic and Evolutionary Biology Program and Biology Department, University of Massachusetts, 611 North Pleasant Street, Amherst, MA 01003-9297, USA

View larger version (15K): [in a new window]   Fig. 1. Silhouettes of dogfish fast-starts. The first 280 ms of a fast response (left panels) and a slow response (right panels) are shown. Numbers indicate time in ms after the onset of the response. Note the faster rate of bending in the fish on the left panels when compared with the right panels, i.e. the fish's shape in the fast response after 120 ms is similar to the fish's shape after 200 ms in the slow response.

View larger version (28K): [in a new window]   Fig. 2. Midline and centre of mass (red circles) of the fish at 40 ms intervals from the onset of the response. Head is indicated by the arrow. A and B correspond to the fast and slow responses, respectively, shown in Fig. 1. C and D show large turns achieved by fast and slow responses, respectively. Note the longer time taken by fish in B and D in order to achieve a similar stage 1 angle as A and C, respectively.

View larger version (12K): [in a new window]   Fig. 3. The relationship between stage 1 angle and stage 1 duration in fast responses (open triangles), slow responses (filled diamonds) and routine turns (open circles). (A) Y=0.40+10.8X, P<0.001, r2=0.91, N=7; (B) Y=0.17+17.4X, P<0.001, r2=0.92, N=8. (C) Y=0.15-34X, P<0.05, r2=0.90, N=4.

View larger version (13K): [in a new window]   Fig. 4. Frequency distribution of maximum head turning rates during stage 1 (A) and stage 2 (B). Stage 1 distribution shows a bimodal pattern, where slow (open bars) and fast (filled bars) responses are present, in line with Fig. 1. The distribution of stage 2 maximum head turning rate shows that slow (open bars) and fast (filled bars) responses overlap.

View larger version (16K): [in a new window]   Fig. 5. (A) The relationship between mean S1 head turning rate and centre of mass (CM) turning rate (open squares, slow responses; filled triangles, fast responses). (B) The relationship between turning rates and stage 1 duration (filled diamonds, CM turning rate in fast responses; filled squares, CM turning rate in slow responses; open diamonds, mean S1 head turning rate in fast responses; open squares, mean S1 head turning rate in slow responses). The dotted line represents the regression between CM turning rate in slow responses and stage 1 duration (Y=1.63+1044X; r2=0.61; P<0.05; N=8). The continuous line represents the regression between mean S1 head turning rate in slow responses and stage 1 duration (Y=-0.36+342X; r2=0.64; P<0.05; N=8). (C) The relationship between speed (UT) and turning rates (filled diamonds, CM turning rate in fast responses; filled squares, CM turning rate in slow responses; open diamonds, mean S1 head turning rate in fast responses; open squares, mean S1 head turning rate in slow responses).

View larger version (19K): [in a new window]   Fig. 6. Examples of performance in fast (A) and slow (B) responses. Head turning rates (continuous lines) and speeds (dotted lines) are shown. Time `0' indicates the beginning of the escape response. In both responses, stage 1 and stage 2 end when the turning rates cross zero, at approx. 0.12 s and 0.25 s, respectively.

View larger version (13K): [in a new window]   Fig. 7. Frequency distributions of distance-derived performance in slow (open bars) and fast (filled bars) responses. (A) Cumulative distance (dT); (B) maximum speed (UT); (C) maximum acceleration (AT). While fast responses show significantly higher performance in all these variables (Table 3), the values for slow and fast responses overlap in the distributions.

View larger version (13K): [in a new window]   Fig. 8. Turning radius in dogfish compared with the turning radius of other vertebrates. All data are means, except for data on sealion, which are means of the 20% smallest radii. Data on fish are based on Domenici (2001), Gerstner (1999) and Walker (2000). Data on cetaceans are based on Fish (1997), as reported by Domenici (2001). Data on sealion are from Fish et al. (2003). Modified from Domenici (2001).

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