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Effects of metamorphosis on the aquatic escape response of the two-lined salamander (Eurycea bislineata)

Emanuel Azizi^1,* and Tobias Landberg²

¹ Graduate Program in Organismic and Evolutionary Biology and
² Biology Department, University of Massachusetts, Amherst, MA 01003-9297, USA

View larger version (12K): [in a new window]   Fig. 1. Bending coefficient. Dorsal view of salamanders at maximum curvature demonstrating three escapes (A–C) with varying bending coefficients. Bending coefficient (BC) is defined as the ratio of head-to-tail chord length (CL; dashed line) to total length (TL) subtracted from 1: BC=1–(CL/TL). To view video clips of escape responses, refer to the supplemental information section of the Journal of Experimental Biology website (http://jeb.biologists.com).

View larger version (20K): [in a new window]   Fig. 2. Lateral view of larval (A) and adult (B) Eurycea bislineata. Tail aspect ratio (AR) is defined as the ratio of the square of maximum tail height (H) to lateral surface area (LSA) of the tail (shaded); AR=H2/LSA. (C) Aspect ratio versus total length. Aspect ratio differs significantly (P=0.0007) between larvae () and adults () but is not significantly correlated with total length (P=0.4593; one-factor ANCOVA). Scale bar, 1 cm.

View larger version (12K): [in a new window]   Fig. 3. Mean bending coefficient (± S.E.M., N=7–11 escapes) for each individual plotted against total length. Bending coefficient differs significantly (P=0.0007) between larvae () and adults () but is not significantly correlated with total length (P=0.1767; one-factor ANCOVA).

View larger version (14K): [in a new window]   Fig. 4. Stage 1 duration (A), stage 2 duration (B) and total escape duration (C) versus total length. Mean values calculated for each individual are plotted ± S.E.M. (N=7–11 escapes). Equations of linear regressions for stage 1 duration are y=5.45x+19.8 (r2=0.32, P=0.051) for larvae (open circles and dashed lines) and y=4.03x+47.2 (r2=0.50, P=0.076) for adults (filled squares and solid lines). Equations of linear regressions for stage 2 duration are y=11.5x+12.1 (r2=0.38, P=0.025) for larvae and y=10.3x+34.8 (r2=0.663, P=0.026) for adults. Equations of linear regressions for total escape duration are y=16.9x+31.9 (r2=0.40, P=0.02) for larvae and y=14.3x+82.1 (r2=0.72, P=0.016) for adults. For results of one-factor ANCOVA, refer to Table 2.

View larger version (13K): [in a new window]   Fig. 5. Distance covered in stage 2 versus total length. Mean values calculated for each individual are plotted ± S.E.M. (N=7–11 escapes). Equations of linear regressions for stage 2 distance are y=0.482x+0.0097 (r2=0.69, P=0.0002) for larvae (open circles and dashed line) and y=0.380x+0.274 (r2=0.91, P=0.0008) for adults (filled squares and solid line). Distance travelled in stage 2 does not differ significantly between the two life stages (P=0.196). Stage 2 distance is significantly positively correlated with total length.

View larger version (38K): [in a new window]   Fig. 6. Polar histograms showing the distribution of head angle at the end of stage 1 (stage 1 angle) (A,B) and stage 2 (final escape angle) (C,D) respectively for larvae (A,C) (N=108) and adults (B,D) (N=51). The number of escapes within 10° intervals increases linearly. The data are standardized so that the salamander’s head is initially aligned at 0°, the stimulus is at 270° and all escapes begin in the clockwise direction. For each polar plot, all escapes from a given life stage are pooled. Stars represent mean values for each life stage and error bars are 95 % confidence intervals. The 95 % confidence intervals for the mean final escape angle of both larvae (C) and adults (D) overlap with 90°, indicating that neither is significantly different from 90°.

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