FERRY-GRAHAM, L.A.*; GIBB, A.C.; California State Univeristy/Moss Landing Marine Labs; Northern Arizona University: Do teleost fishes with different mechanisms of premaxillary protrusion produce functionally similar behaviors?

Premaxillary (upper jaw) protrusion in teleost fishes is a key innovation thought to improve prey-capture performance, although the mechanisms underlying this behavior are poorly understood. We examined phylogenetically disparate taxa representing three teleostean jaw protrusion types: Danio rerio, an ostariophysan (cypriniform type); Gambusia affinis, an atherinomorph (cyprinodontiform type); and Betta splendens, a percomorph (acanthopterygian type). The mechanism in Danio is independently derived, while the mechanism in Gambusia is likely secondarily derived from the acanthopterygian mechanism. Species were imaged capturing prey at 250-500 fps and cephalic movements quantified. Danio exhibit the least anterior protrusion of the premaxilla, and only produce half the displacement of other two species. The path of premaxillary protrusion is similar in Betta and Danio, with the jaw protruding anteriorly and slightly dorsally. In these two species the descending process of the premaxilla swings forward to occlude the sides of the open mouth creating gape profiles approaching 180 degrees. Absolute premaxilla displacement in Gambusia is similar to Betta, but protrusion occurs in an anterior-ventral direction and the descending process of the premaxilla does not swing anteriorly. We conducted an anatomical survey of taxa closely related to these three species to determine the generality of our findings, and to test the alternate hypothesis that these differences are specializations for feeding on particular prey. Our preliminary analysis suggests that these taxa are good representatives of the three modes of protrusion, irrespective of diet and habitat. Thus, we suggest that the differences among taxa may be functional consequences of differences in the underlying mechanisms of protrusion.