Price, C.L.*; Meyers, J.J.; Herrel, A.; Nishikawa, K.C.: Scaling and kinematics of tongue projection in chameleons

Within a year from hatching, chameleons can grow up to two orders of magnitude. This rapid increase in body size likely imposes constraints on the function of chameleon muscles used for prey capture. In this study, we looked at the possible structural and functional constraints of prey capture kinematics associated with body size. Constraints on the feeding system are likely high, as unique, ballistic tongue projection requires accurate control of the jaw and hyolingual apparatus. Mass, SVL, jaw length and head width, were measured in order to identify patterns of growth. Feeding sequences of each chameleon were filmed at 250 frames per second with a high-speed digital video camera. Movement, velocity and acceleration of the jaw and the hyolingual apparatus were quantified. Several species of chameleons were studied, including C. jacksonii, C. melleri, C. oustaleti, C. fischeri and C. calyptratus, which varied in size from approximately one gram to 200 grams. Our analysis showed that the kinematics of prey capture in chameleons scale allometrically with body size. The data were graphed against mass, which yielded a linear regression. The slope values were equivalent to slopes predicted by elastic similarity for allometric growth. Change in maximum tongue projection and maximum hyoid protrusion can be explained by allometric growth. The scaling of maximum gape distance showed slight negative allometry. Analyses of EMG and muscle force measurements will be used to test these predictions further.