Cranial kinematics and prey-type effects in Amia ocellicauda feeding strikes

Variability in the biomechanics and kinematics of prey capture in vertebrates has been studied extensively, with evidence of multiple strategies for successful feeding in many taxa. Early research into suction feeding strikes in fishes hypothesized that fish utilize a set of pre-programmed strike kinematics that cannot be altered once initiated. However, more recent evidence has demonstrated that teleost fishes not only deploy unique strike kinematics for different prey types, but that they also alter their kinematics in response to a prey item attempting to escape. It has not yet been explicitly investigated whether non-teleost actinopterygians can also modulate the strike in response to different prey types. Here we examined the kinematics of suction strikes in bowfin, Amia ocellicauda, a holostean fish most closely related to gars. We recorded Amia feeding on both feeder fish and worms, two types of live prey differing in evasiveness, using X-Ray Reconstruction of Moving Morphology (XROMM). We found significant prey type effects on the magnitude, timing, and velocity of jaw opening, hyoid arch depression, and pectoral girdle motions. These prey type effects demonstrate that the ability to modulate feeding strikes evolved early in actinopterygian fishes, and is possibly the ancestral state for jawed vertebrates.

Methods
XROMM data collection, tracked using XMA Lab version 1.5.5 and exported with 50Hz filter. Rigid body and 3D point transformations were then applied to bones meshes in Autdesk Maya 2020 and analyzed using R Version 4.3.1.