The impact of size and ontogeny on suction feeding kinematics in the axolotl ( <i>Ambystoma mexicanum</i> )

Size impacts all aspects of life in animals. Not only does it impact metabolism and physiology, it also affects movements, resulting in different selective pressures on animals of diverse sizes. However, beyond size, differences in developmental stage may also impact movements due to the maturation of the nervous and musculoskeletal systems. Here, we tested the influence of size and ontogeny on suction feeding kinematics in adults, juveniles, and larvae of the axolotl (Ambystoma mexicanum) using high-speed video recordings. Our data show that size had an influence on nearly all kinematic variables examined, but kinematics often deviated from the predictions of simple geometric scaling models. Moreover, for both the velocity and acceleration of mouth and hyoid movements, the effect of size differed according to the developmental stage. While overall movements were faster in larger animals, the velocity of movement increased faster with size in adults. This could be explained by the fact that the skull undergoes changes at adulthood due to partial remodeling. Changes in velocity are possibly linked to a shift in diet at adulthood from static to more elusive prey, yet this remains to be tested.