Ecomorphology and the Evolution of Phenotypic Divergence in Sunfish

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A successful individual must function trophically (i.e. to eat but not be eaten) as well as reproductively (i.e. to mate and produce successful offspring). These strong and sometimes divergent pressures can create trade-offs between the optimal phenotypes for foraging versus reproduction. However, it is seldom possible to study the concurrent effects of sexual and trophic selection on the evolution of morphology. Recent laboratory and comparative studies show that morphological variation in bluegill sunfish , Lepomis macrochirus, is intimately related to both reproductive and foraging success. The data suggest that females adapt morphologically to the demands of the foraging niches of lakes whereas the morphology of nesting males responds to changes in the intensity of intrasexual selection. The proposed research investigates the interaction between selection on trophic morphology and sexual morphology in bluegill. Morphological and behavioral comparisons among populations collected from different lake types will correlate phenotypic variation in feeding and reproductive abilities. Experimental crosses and common garden rearing of young will attempt to identify a genetic basis for phenotypic variation. A manipulation of nesting male density in a natural lake will assess the degree of behavioral and morphological flexibility of individual males, and quantify the relationship between phenotype and nesting success under different social conditions. This research may eventually address critical questions about the relative importance of sexual selection and trophic radiation in the evolution of the genus lepomis.