Meeting Abstract
During suction feeding in fishes, musculoskeletal linkages and levers transform muscle shortening into cranial expansion. These linkage theories were developed from morphology, manipulation and modeling, and assessed in vivo with high-speed film, video and 2D cineradiography. Now a new X-ray imaging method, X-Ray Reconstruction of Moving Morphology (XROMM), is making it possible to determine the 3D motions of bones and examine the proposed linkages directly. To explore the utility and limitations of XROMM, we have analyzed the opercular linkage, one of several linkages thought to contribute to lower jaw depression. In this linkage, shortening of the levator operculi muscle is hypothesized to rotate the operculum caudodorsally about the operculohyomandibular joint, generating retraction of the interoperculum and the interoperculomandibular ligament, and resulting in depression of the lower jaw about the quatromandibular joint. From XROMM animations of largemouth bass feeding on goldfish, we confirmed that the operculum rotates relative to the suspensorium while the levator operculi shortens, as predicted. However, when kinematics were viewed relative to the fish’s body, the suspensorium clearly rotated rostrodorsally away from the operculum as the neurocranium elevated, and the operculum was stabilized by the levator operculi. Thus, while skeletal motions conform to the expectations of the opercular linkage, the epaxial muscles elevating the head provided the motion for jaw depression, rather than the levator operculi. We expect that the function of this linkage will vary substantially in other species, and that XROMM can be used to assess this and other linkages. However, this method is limited as it is currently time-consuming and can only be applied to fairly large fishes.
