Meeting Abstract

P3.68  Thursday, Jan. 6  XROMM analysis of pharyngeal jaw function in Grass Carp, Ctenopharyngodon idella TARRANT, J C*; GIDMARK, N J; BRAINERD, E L; Brown University; Brown University; Brown University James_Tarrant@brown.edu

Herbivory is a challenging feeding mode for vertebrates since they do not innately produce digestive enzymes that can break down cellulose. The herbivorous Grass Carp, Ctenopharyngodon idella (teleostei: Cyprinidae) does not employ significant intestinal fermentation and lacks oral jaw teeth. Thus, they must rely on the action of their pharyngeal teeth for mechanical breakdown of plant material in order to access the digestible cell contents. The Grass Carp pharyngeal apparatus appears well suited to this task: each hemimandible (derived from ceratobranchial V) consists of 4 multi-cusped teeth. A second row of two small teeth are also present. The four primary teeth from the left and right sides interdigitate during mastication. Two major muscles retract and elevate the jaw, pulling these saw-blade like teeth into occlusion with a keratinous pad on the base of the neurocranium. Since all Cyprinid pharyngeal teeth are embedded deep within the pharynx, their kinematics have been difficult to describe. We used XROMM, a technique that combines biplanar x-ray video with laser scanned bone models (X-ray Reconstruction of Moving Morphology, www.XROMM.org) to reconstruct 3-dimensional, 6-degree-of-freedom kinematics of the pharyngeal jaw in living Grass Carp. We found that the jaws make large mediolateral excursions, grinding food against the opposing pharyngeal pad. Histology shows that this movement results in wear of the tooth enamel. The paucity of appreciable antero-posterior movements is interesting because in most fish pharyngeal jaws are primarily transport organs, not masticatory ones. We show highly rhythmic (CV < 0.2) and fast (2 Hz) chewing cycles, precise occlusion, high-excursion lateral movements and heterodonty in the Grass Carp pharyngeal jaw.