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Selection for Bacillus cereus Infection Survival Using Drosophila melanogaster: Investigation of physiological and Life History Trait Responses
D. melanogaster was developed as a model for resistance to Bacillus infection using B. cereus spores as an agent of artificial selection. Bacillus anthracis spores have been used as a terrorism weapon. Treatment after exposure to these spores is an important goal. B. cereus is a close relative of B. anthracis. Selection was carried out by puncturing adult flies with B. cereus spores and mating the surviving flies. Wound control lines (punctured with a needle dipped into sterile H2O), and a set of untreated control lines, were also generated and used with the selected lines to evaluate selection. The direct response to selection was an approximately 3.3-log increase in the number of spores required to kill half of the flies each generation. Life-history traits (life span, fecundity and developmental time) were investigated in the selected and control lines. There was no effect of selection on life span, but exposure to autoclaved spores reduced life span in all lines. Selected lines produced many more eggs than the other lines when untreated. The difference between lines vanished when they were exposed to autoclaved spore. The results were consistent with the hypothesis of a cost associated with heightened immune responses as a result of introduction of autoclaved spores. The selected line progeny developed relatively slowly which was consistent with the hypothesis of a cost associated with evolved resistance to spores. Or the delayed development could be recognized as an adaption. The selected and wound control lines exhibited an evolved increase in early-age mortality after exposure to autoclaved spores and wounding. This observation has implications for understanding constraints on selection. Respiration as a metabolic trait and movement as a behavioral trait were also investigated. An underlying hypothesis was that the evolution of increased survival after B. cereus infection exerts a metabolic cost, manifest as increased metabolic rate. Selected male flies appeared to have a higher respiration rate than that in control lines. Whereas, females showed a marked increase in respiration after mating, resulting from the provision of oocytes with yolk. Females also move less than males, perhaps due to sexual difference.
Ma, Junjie, "Selection for Bacillus cereus Infection Survival Using Drosophila melanogaster: Investigation of physiological and Life History Trait Responses" (2012). ETD collection for University of Nebraska - Lincoln. AAI3521948.