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Evolutionary Effects of a Eusocial Host Life History on an Endosymbiont


The coevolution between hosts and their endosymbionts (organisms that live only in the host’s body and cells), has dramatically shaped the history of life. Symbiotic relationships can range from mutualism to parasitism, as observed in the diverse relationships between arthropod hosts and obligately intracellular α-proteobacterium from the genus, Wolbachia. Wolbachia bacteria may infect as many as 70% of all insect species where it primarily exhibits reproductive parasitism, thereby inducing female-biased sex ratios to favor its own maternal transmission. In addition to altering host physiology, Wolbachia has been proposed as a pest control and means of mitigating disease vectoring. Despite its abundance and promising applications, the effects of Wolbachia on the development, reproduction, and defensive biology of eusocial insects have remained elusive.

In chapter 1, I explore how horizontal gene migration from endosymbionts to host nuclei may be biased to resolve intergenomic conflicts of interest in favor of the host. This genomic reorganization may help explain why many horizontally transferred Wolbachia genes have become non-functional and why genome reduction is greater in mutualistic strains compared to parasitic strains. Chapter 2 investigates an unexplored relationship between Wolbachia and leaf-cutter ants and potential mechanisms of Wolbachia transfer across host species. The results suggest not all ant-associated Wolbachia strains have the same genetic potential for horizontal transmission. In Chapter 3, I use whole genome sequencing and stage-specific RNA-sequencing to delve deeper into the genomic mechanisms of Wolbachia interactions across host ant developmental stages. Rather than rely on a single process or pathway, this symbiosis likely relies on a symphony of complex interactions that fluctuate over the development of the host. Genome and transcriptome analyses provide a foundation for future research exploring the functional basis and developmental gene expression dynamics for this widespread endosymbiont infecting a dominant tropical herbivore.

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