Comparative dynamics of suction feeding in marine and freshwater three-spined stickleback, Gasterosteus aculeatus: kinematics and geometric morphometrics

Locomotion and feeding are key axes of diversity among fishes, and these are commonly integrated for successful prey capture. However, little is known about biomechanical variation among highly ecologically divergent populations of fishes. Three-spined stickleback, Gasterosteus aculeatus, is an ideal species for teasing apart the relationships between ecology, form and function, given the numerous independent invasions of freshwater lakes and streams from a marine ancestor. These natural replicates afford the opportunity to isolate convergence and/or many-to-one mapping of form to function. To explore the divergence between marine and freshwater stickleback, we investigated the differences in suction feeding kinematics and ram speed among individuals from replicates of both habitats. Feeding sequences were obtained using a high-speed camera, and microcomputed tomography was used to assess three-dimensional geometric morphometrics. Prey capture kinematics of marine and freshwater stickleback differed significantly, with marine individuals consistently exhibiting faster ram speeds, larger gapes, more jaw protrusion, and greater magnitudes and speeds of cranial rotation. These are consistent with an attack strategy aimed at evasive prey. In addition, populations exhibited significant morphological divergence, but not always along the marine– freshwater axis of divergence. Thus, there appears to be a mismatch between morphology and function. Together, our approach has revealed the dynamic kinematic divergence of marine and freshwater stickleback and how functional studies can be used to predict ecology.