Term of Award

Summer 2018

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.


Department of Biology

Committee Chair

J Scott Harrison

Committee Member 1

Edward Mondor

Committee Member 2

Joshua Gibson


The brown widow spider, Latrodectus geometricus (C. L. Koch 1841), has been found to harbor the maternally inherited bacterial endosymbiont Wolbachia pipientis (Hertig and Wolbach 1924), but endosymbiont infection frequency varies widely among Southeastern US populations. Wolbachia is known to manipulate the reproduction of its hosts through male feminization, parthenogenesis, male killing, and cytoplasmic incompatibility. In brown widows, Wolbachia does not alter sex ratios, but any other effects the symbiont has on the spider are unknown. In my first chapter, I assess if there is linkage between Wolbachia infection and maternally inherited mitochondrial DNA (mtDNA) in three brown widow populations. I found no evidence of linkage between Wolbachia infection and mtDNA haplotypes, despite both being maternally inherited. This result is consistent with weak fitness manipulation by the endosymbiont on the host, and could explain the variable, and often low, population infection frequencies in brown widow populations. Lack of linkage could also be the result of common leakage events, in which the bacteria is randomly lost from one generation to the next. In my second chapter, I determine if Wolbachia can induce cytoplasmic incompatibility (CI) in the brown widow. I provide evidence that Wolbachia infection causes partial CI in the brown widow. Weak host effects, such as partial CI, is consistent with the lack of linkage between Wolbachia and mtDNA described in Chapter 1, as well as the variable infection frequencies among populations. In my last chapter, I explore Wolbachia concentrations in brown widow body regions. I found that endosymbiont load did not differ among three body regions, indicating that any host effects are not tissue specific. Wolbachia load, however, does vary among maternal lineages. The observed variation in Wolbachia load among maternal lines should be tested as a possible cause of variation in CI levels among mating pairs. This study may help us better understand the relationship between evolutionary genetics and the strength of host manipulation by endosymbionts.

Research Data and Supplementary Material