Meeting Abstract
Most teleosts possess a lower jaw composed of three fused bones; however, a release of fusion has evolved independently many times, each time creating an intramandibular joint (IMJ) that facilitates contact between the jaw and substrate during food capture. The IMJ may expand the functional repertoire of fishes that possess it; alternatively, an increased ability to exploit a new trophic resource may be accompanied by a decrease in suction-feeding ability. We predict that IMJ-bearing taxa share a reduced reliance on suction-based food capture as well as key functional characteristics of the feeding apparatus. To test this hypothesis, we examined three taxa that have independently evolved an IMJ: Girella, Helostoma, and Poecilia. All three IMJ-possessing taxa have reduced suction performance relative to sister species and share a handful of functional traits (e.g., all exhibit fusion of the cranial bones, relative to non-IMJ bearing sister species). However, each taxon is distinct in certain aspects of food-capture kinematics and mechanics: (1) the IMJ of Girella increases the lower jaw’s mechanical advantage as food is removed from the substrate; (2) in Helostoma, the IMJ allows the formation of a circular gape that makes contact with the substrate at all points simultaneously during scraping; (3) the IMJ of Poecilia generates a large range of motion of the lower jaw, relative to other IMJ-bearing species. We conclude that the movements and mechanical properties of the lower jaw are distinct in each IMJ-bearing lineage, and that differences among taxa are a consequence of different plesiomorphic building blocks in each lineage and/or adaptations to a particular food resource.
