Meeting Abstract

P1.115  Saturday, Jan. 4 15:30  Intramandibular joint (IMJ) bending in Poeciliid fishes: what are the biomechanical properties of the IMJ? JONES, A*; GIBB, A; NAU; NAU aj324@nau.edu

The intramandibular joint (IMJ) is found in the lower jaw of several divergent teleost groups. The IMJ joint serves to increase gape angle and allows the fish to adopt a feeding posture that may increase its likelihood of detecting and avoiding predators. The IMJ of some Poeciliid fishes is unusual in that the Meckel’s cartilage is retained into adulthood and appears to buckle during the depression of the dentary about the IMJ. We examined the biomechanics of the intramandibular joint of the shortfin molly (Poecilia mexicana). We also examined the jaws of the mangrove rivulus (Kryptolebias marmoratus), a distant relative of the shortfin molly, and the Western mosquito fish (Gambusia affinis), a close relative of the shortfin molly, because they maintain Meckle’s cartilage as adults, but lack intramandibular bending. Dissections and clearing and staining of preserved specimens, in combination with segmentation (OsiriX), of 3D CT scans of the cranium were used to describe and quantify the morphology of the lower jaw in all three taxa. We also sectioned and stained the molly and mosquito fish to determine the biochemical and mechanical properties of the Meckel’s cartilage. The physical space between the angular-articular and dentary is quite large in the shortfin molly, whereas the bones of the lower jaw of the mangrove killifish are tightly interdigitated. The physical separation of the two bony elements of the shortfin molly jaw appears to allow the Meckel’s cartilage to buckle, which creates a very large rotation of the dentary (>90°), which forms a large maximum gape. In addition to facilitating our understanding of how and why new joints evolve, it is possible that, because it undergoes numerous, repeated, large magnitude strain cycles within a single day, the shortfin molly could be valuable as a model for the study of degenerative cartilage disease in humans.