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
Keywords	prezygotic Drosophila pseudoobscura evolution reproductive isolation
Date of Defense	2005-07-06
Availability	unrestricted
Abstract 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 speciation.
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