Ecological context of host-microbe interactions

The fields of environmental microbiology and host-microbe interactions have long been studied in isolation. However, at the intersection of these ideas are organisms that acquire their associated microbiota from their environment. Systems with this feature vary greatly in their specificity and in their essentiality. For high-specificity, classical models in symbiosis come to mind, like the reliable acquisition of Burkholderia (sensu lato) symbionts by broad-headed bugs or the recruitment of Vibrio fisheri to the specialized light organ of the bobtail squid. Yet, beyond these one-to-one models eukaryotic organisms interact with myriad microbial species in the environment with low specificity, but high frequency.

Increasingly, fleeting host-microbe interactions are appreciated for their ability to prime host immunity, supplement nutrition, and coordinate development. Several marine invertebrates are induced to settle by non-specific stimuli, including bacterial lipopolysaccharides. Mosquito larvae initiate development in response to microbe-derived B vitamins. Can such non-specific systems show hallmarks of host-microbe co-evolution? Can these relationships be adaptive in their variability (from the host or the microbe perspective) or are some aspects of these interactions cryptically conserved (taxonomically or functionally)?

Mosquitoes spend their whole lives, from egg to adulthood, in the presence of microbes which provide essential signaling for development (constitutive requirement in larvae) and nutrition through direct bacterivory (context-dependent requirement for larvae). Developing in this complex milieu, what other ecological interactions might be at play as both host and microbe are continuously exposed to the other?

For my PhD work I used the aquatic communities housed by carnivorous Sarracenia purpurea pitcher plants to explore these topics. I focused on an obligate inhabitant of these communities, the pitcher plant mosquito, Wyeomyia smithii, and its environmentally-recruited microbiota to ask questions about top-down control of community assembly, ecosystem function, and eco-evolutionary feedbacks between hosts and aquatic microbial communities. I first developed W. smithii as a tractable model in the laboratory, generating germ-free individuals and selectively recolonizing them with pitcher-derived bacteria. I showed that W. smithii hosts a dynamic microbiome over development and that these microbes are essential for host growth. Next, I explored the potential for W. smithii to structure community assembly and function of microbial communities across a natural population of S. purpurea. I demonstrated through manipulation of mosquito density that top-down effects by W. smithii impact essential ecosystem function and bacterial composition in pitchers. Lastly, I considered the importance of W. smithii structuring of ambient microbial pools on host development. I characterized conserved taxonomic signals of host curation at multiple host life stages concomitant with increases in host fitness, supportive of a likely conserved and underappreciated environmental modality by which hosts can adaptively shape their associated microbiomes.

Associated references:

Arellano, A.A., Kashuk, J.†, Lee, J. †, Young, E.B., Coon, K.L. Functional and cross-trophic impacts of bacterial-fungal succession in an aquatic microecosystem. (In prep)

Arellano, A.A.*, Prack, J.L.*, & Coon, K.L. (2025). Host-mediated niche construction of bacterial communities in an aquatic micro-ecosystem. In revision at The ISME Journal

Arellano, A. A., Young, E. B., & Coon, K. L. (2024). An inquiline mosquito modulates microbial diversity and function in an aquatic microecosystem. Molecular Ecology.

Arellano, A.A. & Coon K.L. (2022). Bacterial communities in carnivorous pitcher plants colonize and persist in inquiline mosquitoes. Animal Microbiome.

Arellano, A.A.*, Sommer, A.J.*, & Coon, K.L. (2022). Beyond canonical models: Why a broader understanding of Diptera-microbiota interactions is essential for vector-borne disease control. Evolutionary ecology.

* authors contributed equally
† undergraduate mentee