Tsetse (Diptera: Glossinidae) symbionts: Examining the population dynamics and implications of symbiosis on microbial genomes

Symbiosis refers to two (or more) species living in close association with each other, typically with one on or within the body of the other. Symbioses between microbes and their multicellular hosts are widespread, promoting evolutionary innovation and ecological success. These associations represent a dynamic and wide spectrum, in regards to the necessity, the frequency of occurrence, as well as the physiological impact towards those involved. The tsetse fly (Diptera: Glossinidae), capable of harboring as many as three different species of symbiotic bacteria in addition to the parasitic African trypanosomes, offers an exceptional system to study symbiosis. The intracellular obligate mutualist, genus Wigglesworthia (Proteobacteria: Enterobacteriaceae), is localized within differentiated host epithelial cells (bacteriocytes) that comprise the bacteriome organ stretched alongside the tsetse anterior midgut. The commensal, genus Sodalis (Proteobacteria: Enterobacteriaceae), has a more disperse tissue distribution. Lastly, some Glossina populations can also harbor a third symbiont related to the parasitic microbe Wolbachia pipientis (Proteobacteria: Rickettsiaceae). These three symbionts share unique co-evolutionary histories with their tsetse fly host. My research involved examining and comparing symbiont population dynamics through host larval and adult development and during critical life events (i.e., host mating, immunity challenges, and environmental stress). These symbionts exhibited diverse population densities and dynamics, reflective of varying levels of integration with host biology. I also used these symbiont population dynamics to further elucidate on the functional significance of the particular associations towards tsetse biology. Furthermore, the disparate histories of Wigglesworthia, Sodalis, and Wolbachia also allow for insight into forces driving the emergence of symbiosis and their consequences on the genomic composition of microbial participants. Through a comparative heterologous array approach, the recently established Sodalis was shown to exhibit genetic traits complementary to tsetse biology and reminiscent of the genome tailoring of many intracellular obligate mutualists. The tsetse microbial partners appear to have undergone significant genomic alterations complimentary to their symbiotic lifestyles. The contents of their genomes were also used to further insinuate the biological relevance of the associations.