Meeting Abstract

50.1  Thursday, Jan. 6  Bite force varies with pharyngeal jaw orientation and adductor muscle length in common carp: XROMM and 3D modeling approaches GIDMARK, N J*; KONOW, N; RAINBOW, M; BRAINERD, E L; Brown University; Brown University; Brown University; Brown University nicholas_gidmark@brown.edu

Bite force in vertebrates is expected to vary with gape because muscle force varies with instantaneous muscle length. The pharyngeal jaw system in Cypriniform fishes is well suited for the study of jaw muscle performance as the musculature is relatively simple when compared to other vertebrates. The two main adductor muscles are oriented at ca. 90 degrees to each other, and both are angled ca. 45 degrees to the biting surface. We characterized tetanic muscle force production of the pharyngeal jaw adductors in common carp, Cyprinus carpio in situ. Using XROMM, a technique combining in-vivo biplanar x-ray video with 3D bone reconstruction (X-ray Reconstruction of Moving Morphology, www.XROMM.org), we identify anatomically relevant jaw positions and reconstruct jaw adductor muscle lengths as well as occlusal distances (“gapes”). Using nerve stimulation and a force transducer, we show that a maximally active jaw adductor from a 1kg common carp can generate 20 Newtons at optimum gape (L₀), and that the force generating capacity is quite sensitive to muscle length – a 0.13 cm lengthening of the muscle (past L₀) results in a 20% decrease in tetanic force production. We also find that different teeth in the pharyngeal jaw are capable of generating different gape-specific forces. In light of these data and differences in morphology, we hypothesize functional specialization between teeth within the pharyngeal jaw – anterior teeth seem better suited for crushing and posterior teeth for grinding.