BLANTON, J.M.; GIBB, A.C.; Amherst College; Northern Arizona University: Feeding Behavior of Poecilia sphenops: Kinematics of a novel jaw protrusion mechanism

Upper jaw protrusion in fish is assumed to enhance prey capture by creating forward expansion of the mouth during feeding. Protrusion is theorized to have evolved independently in several lineages, namely the order Cypriniformes and the orders Perciformes and Cyprinidontiformes. For this study, we compared Poecilia sphenops with data previously collected of Danio rerio and Betta splendens (the species represent each lineage: Danio�Cypriniformes, Betta�Perciformes and Poecilia�Cyprinidontiformes). We hypothesized that Betta and Poecilia, because of shared ancestral lineage, would be more similar in feeding behavior to each other than to Danio. Digital images of Poecilia were taken to measure ten head displacement variables during feeding. We used Principal Component Analysis and ANOVA to analyze these measurements. We found Betta and Danio similar to each other, but both significantly different from Poecilia. Poecilia were significantly slower for all timing variables. Displacement variables were larger in Poecilia, excepting cranial rotation and lower jaw displacement. Difference could be due to difference in jaw mechanism. Poecilia has little rotation at the suspensorium-lower jaw joint (where rotation occurs in most fishes), and a secondary, previously undescribed joint in the anterior lower jaw allowing dentary protrusion and flexion. The upper jaw consists of a fixed maxilla ( where movement occurs in other fish, causing premaxillary protrusion) and a premaxilla with extreme protrusion. We propose a new mechanism of lower and upper jaw protrusion and retraction. Such a mechanism could be for specialized feeding �Poecilia is a �nipping� fish, not requiring the jaw strength provided by other mechanisms.