Meeting Abstract
60.4 Saturday, Jan. 5 Adductor muscle function during suction and biting in bamboo sharks. RAMSAY, J.B.*; WILGA, C.D.; Univ. of Rhode Island; Univ. of Rhode Island jasonramsay@mail.uri.edu
The quadratomandibularis (QM) and preorbitalis (PO) muscles of orectolobiform sharks, such as white-spotted bamboos Chiloscyllium plagiosum, are hypertrophied relative to many shark taxa. The PO interconnects the cranium and lower jaw and is thought to assist the QM during jaw adduction by elevating the lower jaw during the compressive phase. However, the hyoidiomandibular ligament in C. plagiosum, present in most Orectolobiformes, couples lower jaw and hyoid depression, yet constrains PO function during the compressive phase. Elevation of the lower jaw also elevates the hyoid due to the ligament connection, and may result in backflow of water and prey in the buccal cavity during the compressive phase of suction feeding, reducing prey capture success. Hyoid, upper and lower jaw kinematics, fascicle shortening and motor activity in the QM and PO and buccal pressure were recorded simultaneously during suction capture and processing bites. During suction capture, active QM shortening begins at peak gape and continues after jaw closure. Active PO shortening begins after jaw closure simultaneously with the onset of hyoid elevation. In contrast, during a bite, active QM and PO shortening begins at peak gape, is slower than during suction capture and does not coincide with hyoid elevation. Jaw closure during suction capture is entirely due to upper jaw protrusion powered by the QM while the PO aids in hyoid elevation during the recovery phase as water is expelled through the gill slits. During a bite, the PO aids in jaw closure contributing to a more forceful bite. All orectolobiform species use suction to capture prey, yet not all feed on hard or tough prey, indicating that PO function in this group may have evolved in response to suction feeding, while modulation of PO function allowed a semi-durophagous lifestyle.
