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Title page for ETD etd-07192012-133204

Type of Document Master's Thesis
Author Colby, Gregory
Author's Email Address gregory.colby@vanderbilt.edu
URN etd-07192012-133204
Title Phylogenetic and population genetic differences between sexual and asexual lineages of Neochlamisus leaf beetles
Degree Master of Science
Department Biological Sciences
Advisory Committee
Advisor Name Title
Daniel J. Funk Committee Chair
Maurine Neiman Committee Member
  • mutation rates
  • DNA
  • sex
  • evolution
  • insects
  • beetles
Date of Defense 2012-07-20
Availability unrestricted
Sex is a major challenge to evolutionary theory, because of the apparent paradox of its ubiquity among multicellular eukaryotes with the substantial evolutionary costs associated with it. The past four decades have seen the development of a large and robust collection of hypotheses purporting to explain the benefits of sex and reconcile this paradox, while empirical research testing the predictions of these hypotheses in nature has only begun to gather momentum more recently.

Neochlamisus leaf beetles are one such natural system with great potential for study of the evolutionary tradeoffs of sexuality and asexuality thanks to the prevalence of gynogenetic asexuality within the genus. Gynogenesis is a form of asexual reproduction in which females require insemination to stimulate the development of unreduced eggs into clonal offspring with no paternal genetic contribution. Gynogenesis requires the coexistence of asexual females with females and donor males of the same nominal species, allowing highly controlled comparisons of ecologically and biologically similar sexual and asexual animals.

In this thesis, I present a new mitochondrial DNA dataset consisting of diverged sexual and asexual lineages of Neochlamisus and describe the phylogenetics and patterns of molecular evolution observed in each lineage, with explicit regard to reproductive mode. I then test two a priori predictions of differences in molecular evolution between the sexual and asexual lineages related to reproductive mode. My results are consistent with a higher rate of accumulation of putatively harmful nonsynonymous mutations in the asexual lineage, and with a selective sweep of the mitochondrial genome in the sexual lineage driven by cytoplasmic incompatibility-inducing strains of the intracellular bacterial parasite Wolbachia.

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