Kinematics of prey processing in Chamaeleo jacksonii: conservation of function with morphological specialization

Abstract

This study develops a model of prey processing behaviours in lizards of the family Chamaeleonidae based on a kinematic analysis of videotaped feeding sequences in a representative species, Jackson's chameleon (Chamaeleo jacksonii). High‐speed video (200 fields per second) and a computerized image analysis system were used, respectively, to film and quantify sequences of three individuals feeding on crickets. Two behaviours, chewing and prey transport, were identified a priori and compared in detail. Analyses of variance revealed significant differences between the two behaviours in seven of 11 kinematic variables. Patterns of correlation of variables within the entire data set were similar to correlations within each behaviour. A principal component analysis on the kinematic variables provided complete separation of the two behaviours in multivariate space. Chewing is distinct from prey transport behaviour in several ways: (1) chewing lacks extensive posterior movement in the hyoid skeleton while the jaws repeatedly open and close against the prey; (2) there is greater mouth opening in chewing; and (3) the entire gape cycle and its components occur more quickly in chewing. Prey transport involves extensive anterior posterior movements of the hyoid skeleton, which reflect the function of the tongue in transporting the prey from the oral cavity into the oesophagus. In both behaviours mouth opening is primarily associated with lower jaw depression rather than head elevation. Maximum hyoid retraction always occurs after peak gape is achieved. The body and head remain stationary with reference to the background, hence no inertial transport occurs. The kinematic profile of prey transport is compared to published feeding cycles of other iguanian lizards and a generalized model of prey processing in amniotes. Prey transport in chameleons follows the same kinematic patterns as reported for other iguanian lizards. We conclude that chameleons possess a generalized food processing system characteristic of other iguanian lizards, largely unmodified despite the presence of an extraordinary prey capture behaviour and its associated morphology.