Date of Completion

8-9-2019

Embargo Period

8-9-2019

Advisors

Chris Simon, Sarah Hird, Joerg Graf, Noah Reid, David Wagner

Field of Study

Ecology and Evolutionary Biology

Degree

Master of Science

Open Access

Campus Access

Abstract

Microbial associations with eukaryotic hosts have been increasingly recognized as an important dimension in understanding eukaryotic adaptation and evolution. Cicadas are hallmark examples as they rely on obligate bacterial or fungal symbionts housed in symbiont-specific organs that provision their deficient xylem-based diets with essential amino acids and vitamins. This kind of symbiosis is prevalent in sap-sucking bugs, yet little is known about the diversity of microbes inhabiting other organs and how microbial composition is structured by host phylogeny and ecology. We surveyed cicada gut microbiota in pure species and hybrids primarily from New Zealand using 16S amplicon surveys and combined these data with a new mitochondrial genome phylogeny in addition to ecological covariates to describe and assess microbial diversity. We find evidence of low abundance microbiota in guts that are highly variable across samples. We did not find significant correlations with host phylogeny, elevation, geographic space, or habitat, although we discuss possible trends for future investigation. In some specimens, we also found highly abundant plant pathogens classified to Candidatus Phytoplasma in New Zealand. Finally, we conclude that the existence of obligate nutritional symbionts in cicadas precludes reliance on gut microbiota and that losses of obligate symbionts are coincident with gains of alternative fungal symbionts domesticated from pathogens. This is highlighted by our finding that all New Zealand cicadas, in addition to three North American species, have high abundances of Ophiocordyceps fungal symbionts in place of the cicada-specific bacterial endosymbiont “Candidatus Hodgkinia cicadicola”.

Major Advisor

Chris Simon

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