PARENT SESSION
Oral Session #90: Evolutionary Ecology.
Presiding: R. del Castillo
Thursday, August 8. 1:00 PM to 3:45 PM. Apache Meeting Room, TCC.

Evolutionary ecology of the trophic polymorphism in Herichtys minckelyi.

Hulsey, C.^*,1, García de León, Francisco², Hendrickson, Dean², ¹ University of California-Davis, Davis² Instituto Tecnológico de Cd. Victoria, Cuidad Victoria, Mexico

ABSTRACT- 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 obtained from fish from eight populations in Cuatrocienegas in Northeastern Mexico. We found papilliform pharyngeal morphs ate a greater percentage of plants 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. Individuals with intermediate pharyngeal morphologies frequently crushed snails 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. The hardness of the shells of snails inhabiting Cuatrocienegas will be contrasted with those of other molluscs. Additionally, we have developed a phylogenetic hypothesis about the relationship of H. minckleyi to other cichlid fishes. By mapping pharyngeal jaw morphology onto this phylogeny we will discuss what is morphologically and functionally novel about the jaw polymorphism in H. minckleyi. We propose that the functional demands placed on this unique species by the ecology of its unique habitat Cuatrocienegas as well as the evolutionary history of this fish have both contributed to the evolution and maintenance of this trophic polymorphism.

KEY WORDS: Cichlasoma. , cichlid, pharyngeal jaw, feeding