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First published online February 27, 2009
Journal of Experimental Biology 212, 768-777 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.026617

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Locomotor–feeding coupling during prey capture in a lizard (Gerrhosaurus major): effects of prehension mode

Stéphane J. Montuelle^1,*, Anthony Herrel², Paul-Antoine Libourel¹, Lionel Reveret³ and Vincent L. Bels¹

¹ UMR 7179 `Mécanismes Adaptatifs: des Organismes aux Communautés', Muséum National d'Histoire Naturelle, équipe `Diversité Fonctionnelle et Adaptations', Département EGB `Ecologie et Gestion de la Biodiversité', 57, rue Cuvier bp55, F-75231 Paris cedex 5, France
² Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA
³ INRIA Rhone-Alpes, 655 Avenue de L'Europe, 38330 Montbonnot, France

View larger version (127K): [in this window] [in a new window]   Fig. 1. Illustration of the kinematic variables quantified in this study. (A) Typical frame extracted from one of the three synchronized high-speed cameras (camera tilted down in oblique dorsal view). (B) Illustration of the gape angle and the elevation of the neck (3-D Z-coordinate of the point NE). (C) Illustration of the head angle. (D) Illustration of the predator–prey distance and the angle of the elbow. UJ, upper jaw; LJ, lower jaw; CM, corner of the mouth; NE, neck, mid-way between the back of the parietal and the pectoral girdle; H, mid-sagittal point between the eyes; O, back of the parietal bones; V1 and V2, two markers, mid-way between the neck marker and the parietal bones and pectoral girdle markers, respectively; EY, anterior corner of the eye; SH, left shoulder; EL, left elbow; W, left wrist (W); P, prey. Scale bar 2 cm.

View larger version (5K): [in this window] [in a new window]   Fig. 2. Scatter plot illustrating the results of a factor analysis performed on the full data set including the kinematic variables of cranial and post-cranial systems associated with prey capture in Gerrhosaurus major. The proportion of the total variance explained by each factor is indicated. Factors 4 and 5 significantly discriminated between capture modes. Open symbols represent tongue prehension events; filled symbols represent jaw prehension events. Squares represent capture events on mealworms, triangles represent the capture of banana, circles represent the capture of grasshoppers and diamonds represent the capture of newborn mice. Variables with loading greater than 0.70 are indicated on the factor axes.

View larger version (26K): [in this window] [in a new window]   Fig. 3. Correlations between strike variables and the multivariate indicators of the kinematics of cranial and post-cranial systems associated with prey capture in Gerrhosaurus major. (A) Predator–prey distance at mouth opening is negatively correlated with factor 5 (P<0.01), indicating the head flexion and the maximal gape are quicker when the prey is closer. (B,C) Peak strike velocity is negatively correlated with both factor 5 (negatively; P=0.01; B) and factor 6 (positively; P=0.02; C), indicating quick cranial movements and wide extension of the elbow are major components of strike velocity. (D,E) Time to peak strike velocity is positively correlated with both factor 4 (P<0.01; D) and factor 5 (P=0.03; E), indicating late peak strike velocities are associated with slow cranial movements. Open symbols represent tongue prehension events; filled symbols represent jaw prehesion events. Squares represent capture events on mealworms, triangles represent the capture of banana, circles represent the capture of grasshoppers and diamonds represent the capture of newborn mice. Variables with loading greater than 0.70 are indicated on the factor axes.

View larger version (10K): [in this window] [in a new window]   Fig. 4. Correlations between multivariate indicators of the kinematics of cranial and post-cranial systems associated with prey capture in Gerrhosaurus major. (A) During jaw prehension events, a significant negative correlation was observed between post-cranial factor 4 and cranial factor 3 (P=0.05). This indicates the timing of flexion of the head and the elbow are coupled. Note that correlations are independent of prey type. (B) During tongue prehension, a significant negative correlation was observed between post-cranial factor 2 and cranial factor 2 (P<0.01). This indicates a greater elevation of the neck is associated with a faster strike, and thus reflects the functional coupling between the jaw and locomotor systems. Squares represent capture events on mealworms, triangles represent the capture of banana, circles represent the capture of grasshoppers and diamonds represent the capture of newborn mice. Variables with loading greater than 0.70 are indicated on the factor axes.

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