INVESTIGATING MICROBIOME ASSEMBLY AND ITS IMPACT ON THE PHYSIOLOGY OF AEDES ALBOPICTUS (DIPTERA: CULICIDAE)
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2024
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Mosquito-borne disease is a major public health burden globally despite decades of efforts towards its eradication. Mosquitoes are difficult to control and many of the most important vectors of human pathogens have developed resistance to conventional insecticides—highlighting the urgency to find novel ways to control mosquito-borne diseases. In recent years, the mosquito microbiome has been the subject of intense study and has revealed interesting insights into its role in mosquito biology. The microbiome is highly influential in shaping many biological processes of mosquitoes including development, fecundity, immunity, metabolism, and nutrient acquisition. Much of a host’s microbiome is derived from the environment; thus, the composition of the environmental microbiome is an important driver of host microbiome composition, which could lead to phenotypic heterogeneity between mosquito populations on the landscape—further complicating control efforts. In Hawaiʻi, the non-native and highly invasive mosquito, Aedes albopictus, is well established, but microbiome-driven phenotypic heterogeneity in populations is not well understood. Therefore, I developed three projects to explore how exposure to compositionally manipulated environmental microbiomes impact A. albopictus biological and physiological processes. The first project involved the reintroduction of environmental bacteria to an A. albopictus colony that was originally isolated from Mānoa, Oʻahu, Hawaiʻi and had been in the laboratory for 15 generations. To vary the environmental microbial community composition, a series of filters were implemented to manipulate the community by cell size that included: a 10 μm regimen, a 2 μm regimen, a 0.1 μm regimen, and a Millipore filter. Mesocosms were created from the filtrates and A. albopictus were reared as larvae into adulthood. Using generalized linear mixed models (GLMM), microbiome α- and β-diversity of the adults from each mesocosm was investigated. The mesocosm microbiomes were also compared to wild A. albopictus pupae that were collected in the environmental water and to wild A. albopictus adults collected near the habitats. The results showed that α-diversity did not differ between the filtered mesocosms; however, the microbiomes of mesocosms were significantly different from wild pupae and from wild adults. The β-diversity analysis showed that the microbiomes of the 10 μm and 2 μm mesocosms formed a single group, the 0.1 μm and Millipore mesocosms formed a single group, wild pupae formed a single group, and wild adults formed a single group. Development times were also measured. Pupation occurred 1.59 days earlier in the 10 μm and the 2 μm mesocosms compared to the 0.1 μm and Millipore mesocosms. The ability of adults to survive under starvation was also impacted by the mesocosm from which they emerged. Adults from the 0.1 μm and Millipore mesocosms survived approximately twice as long as those from the 10 μm and 2 μm mesocosms. These findings demonstrate that exposure to compositionally distinct environmental microbiomes impact i) the assembly of the host microbiome and ii) important biological processes within the host in different ways.
In the second project, a more comprehensive exploration of the A. albopictus microbiome was performed. Mosquitoes collected from Makiki, Oʻahu, Hawaiʻi and their microbiomes were sequenced using the bacterial 16S rRNA gene and the microbial fungal internal transcribed spacer (ITS) gene. Three networks were generated: a 16S only network, an ITS only network, and a cross-domain network. To test the stability of the networks, attacks on the networks were targeted at the centrality measures of node degree (a measure of how many connections one node makes to another node) and betweenness (the total number of shortest paths from node to node). The cross-domain network showed the highest stability in the face of attacks, remaining more stable as more nodes removed from the network. A keystone species analysis was also performed using the same centrality measures and of the six highest taxa fungi comprised five of those, further indicating the importance of fungi in the A. albopictus microbiome. Using the hypothesis that fungi were influential in the stability of the microbiome, a similar experiment to project one was conducted but added a 30-50 μm filter that allowed for environmental fungi to pass into the filtrate. β-diversity was assessed using GLMMs and the presence of fungi in the filtrate led to different microbial communities structures than when fungi are not present. Those results are interesting not only because they validate and support the theoretical network models that generated the hypothesis but emphasize the necessity of including fungi in A. albopictus microbiome studies.
The third project investigated the impacts of developing in compositionally distinct microbial habitats on critical physiological processes in A. albopictus. Those processes were development time, development success, fatty acid synthesis, the ability to survive under starvation, and immune function. All physiological processes were impacted by exposure to compositionally distinct environmental microbiomes and varied by filtration level. Furthermore, the ability to withstand starvation and immune expression, both measured in adult mosquitoes, was impacted by the sex of the mosquitoes and also varied by filtration level. Overall, this study highlights the importance of exposure to compositionally distinct environmental microbiomes on A. albopictus physiology. Furthermore, these findings emphasize the need to include fungi, which are often omitted, in A. albopictus microbiome experiments because of their importance in structuring the microbiome.
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Zoology, Entomology, Microbiology, Aedes albopictus, Immune, Medical entomology, Microbiome, Mosquito, Physiology
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125 pages
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