Term of Award

Fall 2012

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Department

Department of Biology

Committee Chair

Edward B. Mondor

Committee Member 1

Denson K. McLain

Committee Member 2

Stephen P. Vives

Committee Member 3

Stephen P. Vives

Abstract

Many organisms live in transient or permanent aggregations to reduce individual predation risk. Hamilton's "Selfish Herd" theory states that an individual should assume a central position within a group to decrease individual predation risk relative to that of its neighbors (i.e., individuals should be selfish). This theory, however, cannot predict the spatial distribution of individuals within clonal aggregations, that is, when individuals are genetically identical (the "evolutionary self"). As aphids (small, herbivorous insects) are parthenogenetic, emit alarm signals, and have high levels of phenotypic plasticity to cope with environmental stressors like predation risk, they are a model organism for investigating the influence of predation risk on clonal aggregations. This research quantifies the proximate ecological factors that influence the feeding site choices of individual aphids within their natal colony and how these factors influence the spatial distribution of individuals after signals of increased predation risk. Here, I find no evidence for a foraging-predation risk tradeoff in feeding site selection within aphid colonies. Predation risk is greatest at particular feeding sites, and juvenile aphids gain no direct fitness benefits from feeding at these "dangerous" sites. When colonies detect an alarm signal, (E)-β-Farnesene (EBF), individuals drop off of the plant and disperse to "safer" feeding sites away from the natal leaf. When solitary pre-reproductive individuals detect EBF, their future offspring occupy "safer" feeding sites within the natal colony or disperse from the natal leaf (i.e., transgenerational behavioral plasticity). These experiments suggest that selfish behaviors (i.e., which aid in individual survival) may also consequently increase survivorship of the clone. These results may help us better understand "Selfish Herd" theory in clonal aggregations.

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