Meeting Abstract

P1-58   -   Kinematics of the intramandibular joint during food capture in Helostoma temminckii Levy, T*; Ferry, L; Arizona State University tlevy2@asu.edu https://morphology.asu.edu/

The intramandibular joint (IMJ) in Helostoma temminckii, also known as kissing gourami, is located in the lower jaw at the articulation of the dentary and angular-articular bones. These fish are known for a ‘kissing’ behavior, facilitated by the IMJ, which allows the jaws to protrude and rotate making the mouth appear to look like pursed lips. The IMJ has independently evolved in the teleost lineage multiple times, and the mechanics are slightly different in each lineage. In kissing gourami, there are no muscular connections to the region of the lower jaw anterior to the IMJ, thus the IMJ is something of an enigma in terms of how it is mobilized during feeding, and moreover returned to a resting state after feeding. We used high-speed video to examine how the IMJ facilitates jaw protrusion in coordination with the quadratomandibular (QMJ) joint. Individuals were filmed from a lateral and ventral view simultaneously during food capture. From our data, it appears that the IMJ and QMJ are actuated in a sequence, as opposed to in tandem, as we had previously hypothesized. Lateral expansion at the location of the IMJ appears to occur in tandem with rotation about that joint; however, lateral expansion in this species is also rather slight due to their extremely rigid heads. From the kinematic data we have developed a model for how the IMJ is actuated based upon the sequence of expansion and tension created by the rigidly connected skeletal elements.