P3.102 Friday, Jan. 6 Bite force limitation by the length-tension relationship of skeletal muscle in three cyprinid fish species GIDMARK, NJ*; TARRANT, JC; KONOW, N; BRAINERD, EL; Brown University email@example.com
The force production of a muscle varies based on its instantaneous length; therefore jaw position, specifically jaw gape, should impact bite force. Such changes in muscle length can alter bite force either statically, based on prey size, or dynamically, based on jaw kinematics during chewing. We used XROMM, an in-vivo skeletal imaging technique, to quantify 6-degree-of-freedom movements of the pharyngeal jaws and neurocranium in-vivo for three cyprinid fish species. We mapped the origins and insertions of five representative fibers within the main pharyngeal jaw adductor, which we used as a proxy for whole muscle length. Following in-vivo experiments, we combined XROMM in-situ with a muscle stimulation protocol to determine the tetanic length-tension relationship for the same muscle in the same set of individuals. The adductor muscles of all species examined operated at short lengths (on the ascending limb of the length-tension curve) during in-vivo food processing, resulting in submaximal bite forces. The ranges of operating lengths corresponded to 55-73 percent of maximum force in black carp (Mylopharyngodon piceus, a molluscivore, feeding on small manufactured food pellets), 62-79 percent of maximum force in common carp (Cyprinus carpio, an omnivore, feeding on small manufactured food pellets), and 18-100 percent of maximum force in grass carp (Ctenopharyngodon idella, an herbivore, feeding on thin blades of grass). The wider range of in-vivo jaw adductor operating lengths in grass carp is caused by greater jaw motion and muscle strain during chewing. The consistent operation of these adductor muscles at lengths shorter than would be optimal for force production is surprising, and may be related to maintenance of muscle stability at the level of the sarcomere.