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Title page for ETD etd-09222014-113956

Type of Document Dissertation
Author Lawson, Sarah Page
Author's Email Address sarah.p.lawson@vanderbilt.edu
URN etd-09222014-113956
Title A comparative approach to understanding the evolution of social behaviour using Pemphigus aphids as a model system
Degree PhD
Department Biological Sciences
Advisory Committee
Advisor Name Title
Kenneth Catania Committee Chair
Antonis Rokas Committee Member
Jay Evans Committee Member
Julian Hillyer Committee Member
Patrick Abbot Committee Member
  • Pemphigus
  • gall-forming aphids
  • social evolution
  • altruism
Date of Defense 2014-09-12
Availability unrestricted
This research utilizes aphids to address some of the emerging themes in social evolution. To begin to address these themes, I identified traits to measure sociality in aphids. I found that for the ecological and behavioural traits tested, housekeeping and defense, there were quantifiable differences between social and nonsocial species. However, there was no clear threshold that differentiated social from nonsocial species, meaning that definitions of sociality in aphids depend in part on the traits that are measured. Next, I explored a major theme of social evolution, the ability of groups to protect the nest from predators, by characterizing adaptations for defense. I found that aphid soldier elicit an overexpression of the melanization immune response in victims causing toxicity which leads to death, and successful defense of the nest. Finally, cooperation is inherently vulnerable to exploitation by cheaters. Aphids present a rare opportunity to study the effect of cheaters on groups due to multiple unique life history traits. I characterized the consequences of cheaters for weakly and nonsocial species and, contrary to our expectations, the presence of cheaters has the strongest negative effect on the nonsocial species, compared to the social or weakly social species. The results suggest that there is a more complex relationship between competition and relatedness than previously realized. Taken together, these results offers a new perspective on the role of defense, social immunity and kin selection in the evolution of sociality in this disparate group.
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