Meeting Abstract

30.1  Jan. 5  Intramandibular joints help coral reef fishes have a bite KONOW, N*; BELLWOOD, DR; WAINWRIGHT, PC; KERR, AM; Hofstra University; James Cook University; University of California, Davis; University of Guam nicolai.konow@hofstra.edu

Coral reef fishes are more than any other fish fauna characterised by a prevalence of taxa that feed using biting strategies. We investigate the functional morphology of biting in the squamipinnes, a putatively monophyletic assemblage containing nine of the most successful and distinctive coral reef fish families. Using a supertree hypothesis, we demonstrate independent evolution of an intramandibular joint at least five times in this group and discuss the role of this joint in facilitating biting. Character mapping reveals up to seven gains or losses of intramandibular flexion, all associated with trophic transitions between free-living and attached prey. Generalized squamipinnids are commonly suction feeders that lack intramandibular flexion, while atavistic planktivores typically exhibit secondarily derived mandible stiffening. In angelfishes, f. Pomacanthdiae, an intramandibular joint is a basal trait permitting over 35^&deg of mandible flexion, which causes peak-protruded jaw closure. Intramandibular joints in all other squamipinnid taxa function to augment vertical gape expansion during biting behaviours to remove small invertebrates and algae from the reef. In butterflyfishes, f. Chaetodontidae, the origin of intramandibular flexion coincides with a transition from mid-water suction feeding to benthic biting, with flexion magnitude reaching a peak in coral-feeding Chaetodon taxa of the subgenera Corallochaetodon (16�6.6^&deg) and Citharoedus (49�2.7^&deg). A complex evolutionary history appears to have led to the widespread occurrence of intramandibular joints in extant biters, indicating that intramandibular flexion is a major functional innovation that comprise a functional prerequisite to biting in many reef fishes.