Date of Award

May 2016

Degree Type


Degree Name

Doctor of Philosophy (PhD)




Scott Pitnick

Second Advisor

John M. Belote


Drosophila melanogaster, Evolution, Life History, Postcopulatory Sexual Selection, Sexual Selection, Tribolium castaneum

Subject Categories

Life Sciences


Parsing out what makes some individuals more reproductively successful than others is a key pursuit in evolutionary biology. While reproductive success can ultimately be defined as the number of offspring produced over an individual’s lifetime, there are many selective episodes that shape this outcome. Because the majority of animals have multiple mates, achieving matings is but one influence on reproductive success. After copulation occurs, sperm from multiple males compete within the female reproductive tract to fertilize eggs, while females morphologically or behaviorally bias fertilization to preferred males, further shaping reproductive success. Additionally, the act of mating itself may influence parental lifespan or rate of offspring production. Here, I investigate the influence of multiple selective episodes on different aspects of reproductive success in two insects: the fruit fly, Drosophila melanogaster and the red flour beetle, Tribolium castaneum. Established genomes in both systems enabled the generation of transgenic, fluorescently labeled lines: green fluorescent protein (GFP) driven by a ubiquitin promoter in D. melanogaster to look at paternity in eggs, and GFP or red fluorescent protein (RFP) tagged protamines to identify different male’s sperm by head color in T. castaneum. I investigated relationships between different episodes of reproductive success in D. melanogaster and found positive correlations between sperm competitive success and offspring viability; offspring viability itself was influenced by a male × female interaction on hatching success. In T. castaneum, I explored potential drivers of their extremely promiscuous mating system and how that system influences mechanisms of postcopulatory reproductive success. I found that repeated receipt of a complete ejaculate directly benefits female reproductive success, but comes at a longevity cost to males. This direct benefit of remating to females may explain why I found that the proportion of different male’s sperm in the main chamber of the female reproductive tract, and not the specialized sperm storage organ as in D. melanogaster and many other arthropods, determine the proportion of offspring sired by each male. The great differences in postcopulatory mechanics between D. melanogaster, found previously, and T. castaneum, found here, illustrate the importance of mating system in shaping aspects of reproductive success.


Open Access

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Life Sciences Commons