HULSEY, CD*; STREELMAN, JT; Georgia Tech; Georgia Tech: Cichlid Pharyngeal Jaw Fusion: Is Suturing the Key to Unparalleled Trophic Divergence?

The pharyngeal jaw of cichlids and other labroid fishes may represent a key innovation that facilitated their unparalleled trophic divergence. However, the cichlid pharyngeal jaw exhibits a transitional phenotype between the condition found in most bony fish and the morphology in other Labroidei. In cichlids, �fusion� of the lower pharyngeal jaw (LPJ) results from a suture between the two lower ceratobranchials that form a single fused bone in most Labroidei. To examine what novel abilities a fused pharyngeal jaw may confer and also what may have originally favored greater fusion of the labroid jaw, LPJ suturing was examined in Heroine cichlids. Among and within cichlid species, the presence of an external LPJ suture and feeding specialization on mollusks was evolutionarily quite variable, but greater suturing was highly correlated with molluskivory. Both pharyngeal jaw splitting under compression and the forces used to crush mollusks in the wild suggested greater LPJ suturing in the trophically polymorphic Herichthys minckleyi functionally strengthens the pharyngeal jaw. Using 3D computed microtomography (micro-CT), we show that external suturing is a good indicator of the extent the LPJ is sutured internally. During labroid diversification, pharyngeal jaw fusion likely helped to reinforce the LPJ during pharyngeal processing thereby increasing the ability of cichlids to exploit durable prey.