Meeting Abstract

4.2  Saturday, Jan. 4 08:15  Determining the mechanism behind intramandibular bending in Helostoma temmincki FERRY, LA*; GIBB, AC; KONOW, N; Arizona State University; Northern Arizona University; Brown University lara.ferry@asu.edu

The kissing gourami, Helostoma temmincki, is a monotypic, enigmatic tropical freshwater fish, which displays a kissing behavior where the upper and lower jaws protrude and rotate such that the mouth resembles pursed lips poised for kissing. This extreme rotation of the tooth-bearing jaw elements is facilitated by an intramandibular joint (IMJ) located within the lower jaw. During feeding, the IMJ enables the jaws to produce gape angles of ~180 degrees, placing the teeth in direct contact with the substrate for scraping. Here, we clarify the mechanism of jaw rotation, and evaluate a model for rotation based upon the 4-bar mechanism previously proposed for other herbivores carrying the IMJ. Karel Liem originally described the input forces for the kissing behavior as dorsal rotation of the neurocranium and contraction of the sternohyoideus, which depresses the lower jaw. During lower jaw depression, force is transferred from the anguloarticular bone of the posterior lower jaw to the upper jaw via the maxilla. This force transfer rotates the maxilla and places tension on the maxilla-premaxilla connection, causing the premaxilla to protrude. The orientation of the anterior lower jaw (dentary) is such that it is rotated into a dorsoventral orientation via flexion of the IMJ, when the anguloarticular is depressed. Additionally, adduction of the suspensorium, which separates the right and left anguloarticular bones, causes the maxilla to rotate laterally, forcing the upper and lower jaw elements to expand laterally like an umbrella. These movements produce the kissing posture, and also the scraping posture used during food procurement.