HULSEY, C/D; HENDRICKSON, D/A; MARKS, J; COHEN, A/E; WILLIAMSON, C/A: Role of Prey Functional Disparity in Maintenance of Fish Pharyngeal Jaw Polymorphism

Polymorphism in feeding structure could be rare because it represents an ephemeral and transitional stage in speciation. Alternatively, intraspecific morphological specialization may be latent in many species and only arise in exceptional ecological settings due to distinct functional demands prey place on predators. In order to unravel these hypotheses, we examined diet specialization in the trophically polymorphic cichlid fish Herichtys minckleyi using gut analysis and stable isotopes obtained from fish from eight populations in Cuatro Ci�negas in Northeastern Mexico. We found papilliform pharyngeal morphs ate a greater percentage of plants and arthropods compared to molariform morphs. Although snail shell constituted some proportion of the gut contents of all jaw types, papilliform morphs are not often crushing snails. Approximately 90% of molariform morph guts contained crushed snails and their isotope signatures differed significantly from papilliform morphs. Individuals with intermediate pharyngeal morphologies frequently crushed snails and have stable isotope values between the molariform and papilliform morphs indicating their diets reflect their intermediate dentition. Using the snail opercula found in the guts, we estimated both the number of snails eaten and force used by individual H. minckleyi to crush snails. By quantifying the condition of amphipods, we also assessed the shredding abilities of the pharyngeal morphs. The hardness of the shells of snails inhabiting Cuatro Ci�negas will be contrasted with those of other molluscs. Finally, the estimated ontogenetic pharyngeal jaw crushing abilities of H. minckleyi will be compared to other molluscivores.