Title page for ETD etd-07122005-095626

Type of Document Dissertation
Author Schully, Sheri Dixon
Author's Email Address sdixon1@lsu.edu
URN etd-07122005-095626
Title The Evolution of Prezygotic Reproductive Isolation in the Drosophila Pseudoobscura Subgroup
Degree Doctor of Philosophy (Ph.D.)
Department Biological Sciences
Advisory Committee
Advisor Name Title
Michael E. Hellberg Committee Chair
David Donze Committee Member
Mark A. Batzer Committee Member
Robb T. Brumfield Committee Member
Christopher Carlton Dean's Representative
  • prezygotic
  • Drosophila pseudoobscura
  • evolution
  • reproductive isolation
Date of Defense 2005-07-06
Availability unrestricted
Newly forming species that have differentiated in allopatry may evolve numerous

barriers that prevent the interbreeding when they come back into contact with each other.

The objective of this dissertation is to evaluate some mechanisms of prezygotic

reproductive isolation in the D. pseudoobscura subgroup. I begin by evaluating how the

evolution of female preferences and male sexual characters lead to reinforcement

between Drosophila pseudoobscura and its congener D. persimils. In particular, I will

evaluate two alternative hypotheses; Preference Evolution and Discrimination

Enhancement, to determine how selection reduces hybridization between these sister

species. Both hypotheses predict a reduction in the overlap of male traits and female

preferences in hybridizing populations; however, the target of selection differs between

the two. Next, I will discuss reproductive isolation as a result of competiton between

gametes, in particular conspecific sperm precedence. Until this study, patterns of sperm

precedence had rarely been examined between divergent populations or subspecies within

a species. I will evaluate conspecific sperm precedence and its role in reproductive

isolation between two subspecies: Drosophila pseudoobscura pseudoobscura and D. p.

bogotana. The final portion of this dissertation examines the rapid evolution of some

proteins potentially tied to the evolution of reproductive isolation. I focus on some

seminal fluid proteins that may play a role in the reproductive isolation of Drsosphila

species. In particular, I examine the rapid evolution of accessory gland proteins in the D.

pseudoobscura subgroup by looking for the signature of positive selection in the genes

that encode them. I will also evaluate the roles of insertion / deletion mutations in the

evolution of these proteins. Together, the chapters of this dissertation contribute to the

understanding of three forms of prezygotic reproductive isolation and their roles in


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