Theses and Dissertations

ORCID

https://orcid.org/0009-0003-4503-3199

Advisor

Ballinger, Matthew J.

Committee Member

Wang, Ying

Committee Member

Dapper, Amy L.

Committee Member

Gordon, Donna M.

Date of Degree

8-13-2024

Original embargo terms

Visible MSU Only 2 Years

Document Type

Dissertation - Campus Access Only

Major

Biological Sciences

Degree Name

Doctor of Philosophy (Ph.D.)

College

College of Arts and Sciences

Department

Department of Biological Sciences

Abstract

Insects and their natural enemies are engaged in a never-ending battle called the ‘co-evolutionary arms race.’ As a part of these contentious interactions, vulnerable insects evolve natural barriers that prevent successful attacks by their natural enemies. In response, natural enemies evolve strategies that overcome these barriers. Occasionally, microbial symbionts will also participate in these relationships by assisting their insect host in defense against natural enemies or by assisting the natural enemy in subduing its prey. Alternatively, microbial symbionts may become contenders themselves in the co-evolutionary arms race by becoming reproductive parasites of their hosts. To mediate successful outcomes in these relationships, microbial symbionts will often employ diverse protein toxins capable of manipulating and/or harming eukaryotic targets. In this dissertation, I study vertically transmitted Spiroplasma symbionts to address pressing questions about the evolution of symbiont protein toxins involved in insect manipulation and defense. In chapter II, I explore the genome of the first strain of Spiroplasma capable of inducing cytoplasmic incompatibility (CI) - a form of reproductive parasitism. I use bioinformatic techniques to look for potential protein effectors of CI and demonstrate that Spiroplasma evolved this intricate form of reproduction manipulation independent of other symbionts. In chapter III, I use bioinformatic approaches to characterize the expansion and diversification of multiple protein toxin families present in Spiroplasma. I identify dynamic evolutionary processes responsible for expanding and diversifying these toxin families and uncover a striking genus-wide association between protein toxin-associated domains in Spiroplasma and Spiroplasma transmission method. In chapter IV, I explore how protein expansion and diversification have influenced toxin function. Through molecular experiments with diverse Spiroplasma ribosome-inactivating protein (RIP) toxins, I implicate neofunctionalization as a common outcome in RIP toxin expansion. Lastly, in chapter V, I focus on the interactions between host and parasite by describing the first parasitoid wasp known to attack the adult stage of Drosophila hosts. This work introduces a new Drosophila-wasp study model for future novel studies into parasitoid-host interactions. Overall, this dissertation addresses broad questions about the evolution and origins of host, symbiont, and natural enemy interactions, and provides new tools and methods for future investigations.

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