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Kinematic analysis of a novel feeding mechanism in the brook trout Salvelinus fontinalis (Teleostei: Salmonidae): behavioral modulation of a functional novelty

Christopher P. J. Sanford^*

Department of Biology, 114 Hofstra University, Hempstead, NY 11549, USA

View larger version (22K): [in a new window]   Fig. 1. Schematic lateral view of the skull of a generalized salmonid showing the tongue-bite apparatus (TBA). For illustrative purposes, the suspensorial and most of the gill arch elements have been excluded and the position of the lower jaw has been artificially lowered to allow all the elements of the TBA to be visible. MJA, mandibular jaw apparatus. The proposed movements of cranial elements during raking are overlaid. A, preparatory phase; B, power stroke; C, recovery phase; SH, sternohyoideus muscle; CBL, cleithrobranchial ligament. Retraction of the pectoral girdle (cleithrum) during the power stroke of raking provides a posterior force on the hyoid via the sternohyoideus and/or cleithrobranchial ligament. See text for details.

View larger version (16K): [in a new window]   Fig. 2. Digitizing protocol for analysis of high-speed video recordings. The seven points digitized are explained in the text.

View larger version (127K): [in a new window]   Fig. 3. Representative sequence of raking in Salvelinus fontinalis showing the extensive elevation of the neurocranium (curved arrow) and retraction of the pectoral girdle (straight arrow) that is typical of this post-capture behavior. The grid is 1 cm square.

View larger version (31K): [in a new window]   Fig. 4. Mean kinematic profiles of the post-capture behaviors, raking and open-mouth chewing, in Salvelinus fontinalis while feeding on crickets. The shaded area represents the power stroke of raking (see text for details). Note that hyoid displacement is towards the lower jaw during raking and away from the lower jaw during open-mouth chewing. Values are means ± S.E.M., N=20.

View larger version (28K): [in a new window]   Fig. 5. Mean values of maximum displacement of kinematic variables for two behaviors (raking and open-mouth chewing, OMC) and three prey types (cricket, fish and worm) in Salvelinus fontinalis (N=20 for each prey type). Values are means + S.E.M. The results of an ANOVA to determine whether behaviors differ within prey are indicated within the graph. NS, P>0.05; *P<0.05; **P<0.01; ***P<0.001. Above each graph are the results of ANOVA post-hoc tests after Bonferroni correction contrasting prey-type differences within behavior. PT Rake, raking; PT OMC, open-mouth chewing.

View larger version (27K): [in a new window]   Fig. 6. Mean values of time to maximum displacement of kinematic variables for two behaviors (raking and open-mouth chewing) and three prey types (cricket, fish and worm) in Salvelinus fontinalis (N=20 for each prey type). Values are means + S.E.M. The results of an ANOVA to determine whether behaviors differ within prey are indicated within the graph. Above each graph are the results of ANOVA post-hoc tests after Bonferroni correction contrasting prey-type differences within behavior (PT Rake, raking; PT OMC, open-mouth chewing). Horizontal bars separate groups that are significantly different. NS, P>0.05; *P<0.05; **P<0.01; ***P<0.001.

View larger version (21K): [in a new window]   Fig. 7. Principal components analysis of (A) raking and (B) open-mouth chewing behavior in Salvelinus fontinalis for 10 derived kinematic (displacement and temporal) variables. Each symbol represents one chewing behavior for one individual: C, cricket; F, goldfish; W, worm. All factor loadings are presented in Table 3. Prey-type polygons are not significantly different for raking (MANOVA, Wilks’ Lambda P=0.65, d.f.=8,108), but are significantly different for open-mouth chewing (Wilks’ Lambda P<0.05, d.f.=6,110).