Meeting Abstract
The study of kinematics explicitly integrates morphology and motion and is vital to our understanding of the evolution of functional systems. However, traditional analytical methods are generally suited for detailed comparison of relatively few taxa. We present a method for evaluating kinesis that treats complex biological motions as a single object, a trajectory of shape change, the properties of which make it amenable to comparative study. We focus on cichlid feeding systems, providing examples of two geometric-based motion analyses. First, we explore the relationship between prey capture kinematics and feeding ecology in African cichlids, using high-speed videos. We find that the amount of kinesis produced (trajectory length) and the efficiency at which it is done (trajectory nonlinearity) are linked to diet, both being greater in species eating more evasive prey types. Second, we introduce a framework for evaluating form-function relationships in biomechanical models, using an example from Malagasy cichlids. By simulating the movements of four-bar linkages, given some input rotation, we can produce motion trajectories as we did in live fishes. We propose that the resulting trajectory lengths may be used as an alternative functional metric to kinematic transmission (KT), a common measure of motion transfer in four-bars. This new metric has the desirable qualities that it measures total output kinesis of linkages and also that it is not ratio-based and therefore not subject to issues of artifactual redundancy previously shown for KT. Our research highlights the potential for geometric morphometrics to address novel questions involving the evolution of biological motions.
