Meeting Abstract
The intramandibular joint (IMJ) is located in the lower jaw of several substrate-feeding teleosts and is typically found between the dentary and angular-articular. This secondary jaw joint allows an increased gape angle, which enables the fish to place its jaws in greater contact with attached prey. The IMJ is well documented in marine fishes like parrotfishes and angelfishes, but data for freshwater fish with IMJs are limited. We compared the biomechanics of the IMJ of the freshwater shortfin molly (Poecilia mexicana), with two non-IMJ bearing species: 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. Dissection, 3D micro-CT scans, and clearing and staining were used to describe and quantify the morphology of the lower jaw. The number of independent bony elements in the lower jaw apparatus appears to be reduced in IMJ-bearing species, while the separation between the angular-articular and dentary is enlarged. Video sequences of feeding events for each species were used to determine the range of motion of the lower jaw and other cranial elements. Bones isolated from micro-CT scans, kinematic data, and the program Blender were used to generate a 3D model of the movements of the IMJ and anterior and posterior elements of the lower jaw during feeding. We predict that bite force and the reliance on suction-based-capture are decreased in the shortfin and other IMJ-bearing freshwater taxa, although we expect IMJ-bearing species will have greater control over lower jaw movements. This study will yield an improved understanding of IMJs in freshwater fish and provide new insight by outlining the biomechanical limitations and advantages of possessing and employing an IMJ during substrate-based feeding.
