HULSEY, C/D; Univ. of California, Davis: Evolutionary Decoupling of Oral and Pharyngeal Jaws in Central American Cichlid Fish

I investigate whether a single species of cichlid fish, Herichthys minckleyi , possesses oral jaw mechanics that vary independently of mechanical and functional specializations in its pharyngeal jaw. One explanation for the unparalleled trophic raditaion in cichlid fishes is that the processing efficiency of the novel cichlid pharyngeal jaws is believed to have functionally freed up the oral jaws to specialize on capturing prey (Liem 1973). However, this assertion concerning the evolutionary decoupling of cichlid pharyngeal and oral jaws was based primarily on observations of macroevolutionary divergence in cichlid jaw morphology and function. For this decoupling to play a role in the initial stages of cichlid trophic diversification, this functional independence must exist on a microevolutionary scale. To this end, I first demonstrate that there are clear functional differences in the ability of the two pharyngeal morphotypes in H. minckleyi to process prey. Then, I examine whether these same functional differences can explain morphological diversification within the pharyngeal jaws of other Central American cichlids using a phylogeny constructed with the cytochrome b gene. With this phylogeny, I also test if structural components of the oral jaws (gape, jaw protrusion, lower jaw lever systems, and the mass of the adductors) are correlated with the evolution of feeding on elusive prey versus attached prey. I then determine if the same oral jaw characters associated macroevolutionarily with diet in all Central American cichlids are also positively associated with feeding on elusive versus non-elusive prey in H. minckleyi . Finally, I test if oral jaw mechanics varies independently of pharyngeal jaw morphology in this one species.