Causes and consequences of microbiome formation in Culex mosquitoes

The guts of aquatic invertebrates host an array of microbes, yet how microbial communities assemble, and how particular microbial taxa influence their host, remains unresolved for many systems, particularly invertebrates. There is no doubt that the environment influences the development of host-associated microbiota, but questions remain regarding how community structure may influence the development of the microbial community within individual hosts. I investigated how competition (intraspecific vs. interspecific) at different densities (20 vs. 40 individuals per 350 mL of 25% grass infusion) in different resource environments (with vs. without added Nitrogen and Phosphorus) shapes the microbiome of larval Culex mosquitoes, as well as how these different environments influence survival to, time to, and size at adulthood. I conducted two types of experiments, both in which I manipulated the resource base and competition. In Chapter 1, I compared free-living microbial communities in the larval environment to the microbial communities in fourth-instar larvae, and in Chapter 2, I compared how varying levels of competition influenced survival during the larval stage, survival to the adult stage, and size at adulthood. In the microbiome study (Chapter 1), I found that the free-living microbial community in the initial environments were similar to each other regardless of resource base (i.e., with vs. without added nutrients), but varied by resource base four days later. The larval Cx. restuans samples also differed in their microbial communities based on the resource base and initial density. However, neither the final free-living communities nor the microbial communities in the larvae were influenced by the type of competition. The larvae’s microbiomes differed from the free-living assemblages, though they showed similar responses to resource base, competition, and initial density. Ten microbial Families (Bacteroidaceae, Campylobacteraceae, Clostridiaceae, Comamonadaceae, Enterobacteriaceae, Flavobacteriaceae, Lachnospiraceae, Porphyromonadaceae, Pseudomonadaceae, and Rhodocyclaceae) accounted for over 90% of the relative abundance in the larval samples. When rearing larvae to adulthood (Chapter 2), isolated larvae reared with higher resource concentration unsurprisingly showed faster development and larger adult body size (indicated by wing length) compared to those reared with lower resource concentration. However, it is possible that this difference simply resulted from nutritional differences (e.g., food quantity and/or quality), rather than larvae in the lower resource concentration treatment lacking specific fundamental microbes. Larvae reared on laboratory-created infusions in competition resulted in lower survival compared to those reared in isolation. For the larvae that did survive to adulthood, there was a significant interaction between competition and resource base; intraspecific competition on the grass infusion resulted in the most rapid development time, but also resulted in smaller adults. Larvae reared individually with the field-collected waters showed highly variable survival to adulthood, time to adulthood, and wing length. These results suggest that manipulating environmental variables can drastically alter the microbiomes of the larvae and their environment, and can lead to a corresponding change in the larval development and adult body size of Culex mosquitoes.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste