Exploring Endosymbiont Biodiversity and Complexity in the Family Cicadidae

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All organisms possess beneficial microbial partners (symbionts) that contribute to their health and survival. Many of these live in the gut and are known as the microbiome. Insect symbionts are theorized to bring new features that allow species formation and habitat invasions. In the case of insects that feed on food lacking important nutrients, highly specialized microbes inhabit organs in the abdomen and provide essential amino acids and vitamins. The major goal of this proposal is to study the interactions between insects and microbes and how they function together in a mutually beneficial relationship. The roles of endosymbionts in speciation and biogeography are largely unexplored and their diversity and evolution is poorly known outside a handful of model systems. This research uses cicadas as a study system because they have a particularly deficient diet and are diverse and spread across the globe. DNA data will be used to construct a dated evolutionary tree to study how the cicadas and their symbiont partners have spread around the world and diversified into new species. This information will be useful in general understanding how microorganisms benefit their hosts and specifically in the study of invasions of beneficial and pest insects of agricultural importance. Biodiversity information for cicadas and their symbionts will be disseminated to scientists and the general public by journal publications, society meetings, and the World Wide Web. Citizen science projects and biology lab exercises will be designed and made available. Future scientists will be trained in multiple laboratories, including one postdoc and two graduate students; many undergraduate participants will interact with scientists internationally via the web. Cicada primary endosymbionts have already been demonstrated to include examples of evolution that are surprisingly different from those of other insects, such as rampant symbiont genome duplication/lineage splitting in diverse cicada lineages followed by complementary gene loss and pseudogene formation. To understand the biogeography and evolution of host-symbiont consortia, an existing cicada phylogeny created previously by the research team involved in this work will be expanded and used as a framework. Ecological and symbiont data mapped onto the tree will test hypotheses about the relative timing of changes in cicada habitat association and symbiont consortium membership. This work asks: 1) Does the gain of a secondary (facultative) endosymbiont facilitate the breakdown and or loss of primary (obligate) endosymbiont? Or, 2) Does the breakdown or loss of the obligate endosymbiont allow the invasion of a secondary endosymbiont? Similarly, 3) Do changes in the gut microbiota affect primary endosymbionts (keeping in mind that gut microbiota are known to synthesize essential amino acids for some hosts). Finally, 4) Is symbiont consortium membership related to changes in the external environment (both biotic and abiotic) such as the invasion of new habitats with different environmental conditions and host plants. Improved high-throughput genomic sequencing methods and probes for conserved endosymbiont genes will simultaneously expand the framework Cicadidae evolutionary tree while generating genetic datasets for both of the primary cicada endosymbionts. Surveys of cicada symbiotic partners using metagenomic sequencing (of bacteriomes and fat bodies for endosymbionts) and amplicon sequencing (of gut contents for microbiome studies) will allow the exploration of microbial and fungal symbiont biodiversity. Our hypothesis testing will facilitate exploration of environmental versus evolutionary drivers of biodiversity innovation. New information on the evolution of bacterial endosymbiont genomes will also be produced.