32.3 Thursday, Jan. 5 Pharyngeal jaw function in three cyprinid fishes GIDMARK, NJ*; TARRANT, JC; BRAINERD, EL; Brown University email@example.com
Cyprinids process food with highly specialized pharyngeal jaws. These jaws bear blade-like teeth in herbivores, molariform teeth in molluscivores, and heterodont dentition in omnivores. We studied food processing in grass carp (Ctenopharyngodon idella; herbivore), black carp (Mylopharyngodon piceus; molluscivore), and common carp (Cyprinus carpio; omnivore) using XROMM, an in-vivo skeletal imaging technique. The pharyngeal jaws have no bony articulations; they are suspended from the pectoral girdle and skull in a muscular sling. In all three species, only two jaw muscles have appreciable mass and appropriate lines of action to adduct the chewing surfaces: the pharyngeal jaw levator and retractor. Previous research has shown that both muscles are electrically active during the chewing stroke. Of those two muscles, we observed lengthening of the retractor and shortening of the levator during occlusion in all three species. We conclude that the levator functions as the primary driver of mechanical food breakdown, while the retractor acts primarily as a jaw positioning muscle. Despite these similarities in muscle actions, the jaws of the three species move differently. Grass carp use rotations and translations (>20 degrees and 4 mm summed across the two primary axes of motion) to abduct the jaws, pulling their ridged teeth laterally across the chewing pad. This shearing motion in grass carp contrasts starkly with the simple, translational movement in black carp, which show less rotation but similar translation. This contrast in jaw kinematics parallels their respective diets: grass carp shear vegetation while black carp crush their snail prey. The morphologically and trophically intermediate common carp shows intermediate movements, and in all three species, the magnitude levator muscle strain parallels the amount of jaw motion.