Meeting Abstract
68.6 Tuesday, Jan. 6 Jaw depressor function during feeding in little skates, Leucoraja erinacea RAMSAY, J.B.*; WILGA, C.D.; University of Rhode Island; University of Rhode Island jasonramsay@mail.uri.edu
The coracomandibularis (CM) and coracoarcualis (CA) muscles of little skates, Leucoraja erinacea are arranged in-series and interconnect the lower jaw to the pectoral girdle. Shortening of the CM and CA should result in lower jaw depression. However, manual depression of the hyomandibulae results in simultaneous jaw protrusion and lower jaw depression, as in other batoid species. Thus, instead of strictly shortening to directly actuating jaw depression, the CM and CA may also contract isometrically or eccentrically; functioning to transfer force and motion from the paired coracohyomandibularis (CHM) muscles to the lower jaw or to absorb force and motion, respectively. Hyomandibulae, upper and lower jaw kinematics, as well as motor activity in the CM, CA and CHM, and fascicle shortening in the CM and CA were recorded simultaneously with buccal pressure during feeding. During prey capture the CM and CA actively shorten with synchronous activation of the left and right CHM, resulting in ventrally directed protrusion of the opening jaws. Prior to peak hyomandibula and jaw depression, the CA actively lengthens while the CM continues to actively shorten resulting in an anterodorsal rotation of the protruding jaws at the articulation with the distal hyomandibulae. In contrast, during prey processing the CM and CA actively lengthen as the hyomandibulae are elevated and gape is decreased; compressing the buccal cavity. A second active period follows, in which the CM shortens as the jaws open and hyomandibulae depress. Modulation of CM and CA activity and strain in L. erinacea suggests that functional plasticity of certain feeding muscles along with muscular duplication and decoupling of the jaws and hyoid, may play a key role in the increased functional versatility in the feeding apparatus of batoids compared to sharks.
