Year of Award

2023

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Organismal Biology, Ecology, and Evolution

Other Degree Name/Area of Focus

Genetics

Department or School/College

Ecology and Evolution

Committee Chair

Brandon Cooper

Commitee Members

Jeff Good, Pat Secor

Keywords

Wolbachia, Drosophila, Cytoplasmic Incompatibility, wMel

Publisher

University of Montana

Subject Categories

Biodiversity | Evolution | Genetics

Abstract

Maternally-transmitted Wolbachia infect the cells of most insect species, but their frequencies in host populations vary. While much of their success can be attributed to their ability to manipulate host reproduction, these manipulations are context-dependent, varying due to several biotic and abiotic factors. Wolbachia’s most common manipulation, cytoplasmic incompatibility (CI), is a conditional sterility phenotype where male-female host compatibility depends on their infection status. Specifically, CI occurs when infected males produce modified sperm that cause increased embryonic lethality unless the female carries a similar infection. Rescuing their eggs from CI increases the relative fitness of infected females, promoting Wolbachia spread to high frequencies. In nature, the strength of CI varies for mostly unknown reasons. This variation is predicted to contribute to variable Wolbachia frequencies in host populations, demonstrating the need to understand the factors that contribute to CI strength. Within populations, theory predicts natural selection does not act to preserve CI, allowing potentially harmful mutations to accumulate and suggesting genetic variation of CI-causing genes (cifs) may contribute to CI. In my first chapter, we compared cifs of closely related Wolbachia strains in Drosophila to test the impact of specific mutations on CI strength. Using transgenics to induce CI, we showed that a single naturally observed mutation weakens CI through reduced enzymatic effects. However, variation in cif sequence cannot fully explain CI strength variation suggesting other factors may influence CI strength. Temperature is a crucial environmental variable that affects all aspects of ectotherm behaviour and physiology. For ectotherms carrying Wolbachia, these temperature effects can influence important Wolbachia-host interactions, such as CI strength. In my second chapter, I estimated the thermal sensitivity of CI strength for four divergent Drosophila-Wolbachia systems to test the impact of temperature on CI strength. For wMel-infected D. melanogaster, I demonstrate for the first time that cold temperatures increase CI strength that does not decline over the first 3 days of male age, in contrast to rapidly declining CI strength with age at warmer temperatures. This thesis adds to the growing body of work describing important Wolbachia-host interactions as context-dependent.

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© Copyright 2023 Kelley Van Vaerenberghe