Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Bryan Neff


The origins of novel traits and their contribution to biodiversity have long been of interest to biologists. My research focused on the links between foraging ecology and both natural and sexual selection, and how these mechanisms interact to shape the phenotypic diversification of natural populations. Using bluegill (Lepomis macrochirus) and pumpkinseed sunfish (Lepomis gibbosus), I examined three major questions: 1) how are diet and morphological variation related to alternative reproductive tactics in bluegill; 2) are sexual selection and disruptive selection driving divergence between foraging ecomorphs in pumpkinseed; and 3) how are human-induced changes to prey communities affecting foraging ecology of pumpkinseed. By examining the alternative reproductive tactics of bluegill, I found that the deeper bodied parental males and females consumed more zooplankton as compared to the littoral diets of the more streamlined sneakers, satellites, and juveniles, the opposite relationship from what is typically observed in fish. However, the morphological and swim performance variation among reproductive groups may increase mating success, indicating that sexual selection may be an important factor in the phenotypic diversification of bluegill. I next examined the relationship between stable isotopes (δ13C and δ15N) in different female tissues (white muscle, liver, and eggs), and found that from pre-fertilization to the day of hatch eggs could be used as a proxy for female diet. By collecting nest guarding males and eggs from their nests it is possible to estimate assortative mating based on foraging tactic. Applying this technique to a wild population of pumpkinseed, I found evidence of phenotypic divergence and assortative mating between foraging tactics. However, there was no evidence of genetic divergence towards speciation, possibly related to weak disruptive selection in this population. Finally, I found that native pumpkinseed sunfish in three populations have undergone substantial shifts in diet following the invasion of zebra mussels (Dreissena polymorpha), consuming considerably more zebra mussels and fewer benthic invertebrates than before the invasion. These results contribute to a growing body of evidence that foraging ecology and its relationships with both disruptive natural and sexual selection play a key role in the evolution and diversification of natural populations.

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