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Otero-Bravo_Dissertation_2020.pdf (4.49 MB)

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Genome Evolution During Development of Symbiosis in Extracellular Mutualists of Stink Bugs (Pentatomidae)

Otero Bravo, Alejandro
http://orcid.org/0000-0002-7598-4943
http://rave.ohiolink.edu/etdc/view?acc_num=osu1586638345682906

Abstract Details

2020, Doctor of Philosophy, Ohio State University, Evolution, Ecology and Organismal Biology.
Nutritional symbioses between bacteria and insects are prevalent, diverse, and have allowed insects to expand their feeding strategies and niches. It has been well characterized that long-term insect-bacterial mutualisms cause genome reduction resulting in extremely small genomes, some even approaching sizes more similar to organelles than bacteria. While several symbioses have been described, each provides a limited view of a single or few stages of the process of reduction and the minority of these are of extracellular symbionts. This dissertation aims to address the knowledge gap in the genome evolution of extracellular insect symbionts using the stink bug – Pantoea system. Specifically, how do these symbionts genomes evolve and differ from their free-living or intracellular counterparts? In the introduction, we review the literature on extracellular symbionts of stink bugs and explore the characteristics of this system that make it valuable for the study of symbiosis. We find that stink bug symbiont genomes are very valuable for the study of genome evolution due not only to their biphasic lifestyle, but also to the degree of coevolution with their hosts. In Chapter 1 we investigate one of the traits associated with genome reduction, high mutation rates, for Candidatus `Pantoea carbekii’ the symbiont of the economically important pest insect Halyomorpha halys, the brown marmorated stink bug, and evaluate its potential for elucidating host distribution, an analysis which has been successfully used with other intracellular symbionts. We find that while increased mutation rates are present, the symbiont loci are not as effective as host loci for these studies. In Chapter 2 we sequenced and analyzed the genomes of four tropical stink bug symbionts belonging to the genus Edessa. The four symbionts show similar levels of genome reduction, reaching 0.8 Mb, five times smaller than the closest free-living relative and over 20% smaller than the genome of P. carbekii. Additionally, we show that they display signatures of amino acid supplementation for their host and that these are a distinct clade from P. carbekii, indicating convergence in many genomic traits of the symbiosis. Chapter 3 expands on chapter 2 by describing 11 more genomes of stink bug symbionts with varying degrees of genome reduction, ranging from those of the previously described symbionts of Edessa to genomes equal in size to their free-living relatives. We identify the multiple stages of genome reduction, including an initial massive pseudogenization, followed by progressive degeneration of metabolic pathways including those involved in cell wall components and amino acid biosynthesis. Finally, Chapter 4 explores a problem with the study of the phylogenetic relatedness of genome reduced symbionts, long branch attraction artifacts, which is prevalent in many of these studies and can have profound implications in addressing the convergence of these traits. We show that our method to identify and analyze separately taxa prone to LBA can address this issue and perform similarly to more sophisticated but also more computationally expensive methods.
Zakee Sabree (Advisor)
Rachelle Adams (Committee Member)
Norman Johnson (Committee Member)
Laura Kubatko (Committee Member)
185 p.
Bioinformatics; Biology
symbiosis; genomics; stink bug; Pantoea; gammaproteobacteria; genome reduction

Recommended Citations

Citations

  • Otero Bravo, A. (2020). Genome Evolution During Development of Symbiosis in Extracellular Mutualists of Stink Bugs (Pentatomidae) [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1586638345682906

    APA Style (7th edition)

  • Otero Bravo, Alejandro. Genome Evolution During Development of Symbiosis in Extracellular Mutualists of Stink Bugs (Pentatomidae). 2020. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1586638345682906.

    MLA Style (8th edition)

  • Otero Bravo, Alejandro. "Genome Evolution During Development of Symbiosis in Extracellular Mutualists of Stink Bugs (Pentatomidae)." Doctoral dissertation, Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1586638345682906

    Chicago Manual of Style (17th edition)

osu1586638345682906
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