Exploring the Predictability of Evolution: Identifying Repeatable Adaptive Traits Across Microbial Communities Público

Abstract

Understanding the predictability of microbial evolution in host-associated environments is crucial for uncovering the mechanisms that drive ecological stability and diversity. In this study, we examined how bacterial communities evolved during association with the nematode Caenorhabditis elegans, focusing on the emergence of repeatable adaptive traits. Using single-species, pairwise, and multi-species (Community G) experimental evolution frameworks, we tracked changes in species composition, colony morphotypes, motility, and growth dynamics across five serial passages.

While Microbacterium oxydans (MO) maintained stable phenotypes across conditions, Chryseobacterium indologenes (CI) evolved alternate morphotypes exclusively in the complex community environment. These alternate CI morphotypes exhibited reduced motility and distinct colony morphologies compared to ancestral strains. Principal Component Analysis revealed early divergence followed by stabilization of community composition, suggesting strong initial selection pressures mediated by the host environment. Logistic growth assays indicated that alternate morphotypes had altered saturation densities, while reversion assays suggested a degree of phenotypic plasticity.

Overall, our findings highlight that microbial evolution in host-associated environments is shaped by species interactions, spatial structure, and host filtering. While some evolutionary outcomes, such as species persistence, were repeatable, others, such as the emergence of alternate morphotypes, were contingent on community complexity. This work advances our understanding of how ecological interactions drive microbial diversity and the predictability of evolution in host-associated systems.

Table of Contents

Table of Contents

Introduction Methods 2.1. Media and Buffers 2.2. Bacterial Strains 2.3. Evolution Experiment 2.4. Motility Assays 2.5. Revertant Collection and Isolation 2.6. Data Analysis     2.6.1. Diversity of Evolving Microbial Communities     2.6.2. Motility Analysis     2.6.3. Logistic Growth Analysis Results 3.1. Bacterial Composition in Single Species, Pairwise, and Community Conditions 3.2. Emergence of Alternate Morphotypes 3.3. Logistic Growth Differences Between Morphotypes 3.4. Motility Differences Between Morphotypes 3.5. Reversion Events and Phenotypic Plasticity Discussion Future Directions Limitations Conclusion Works Cited

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School	Emory College
Department	Biology
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Biology, Evolution and Development
Palavra-chave	c.elegans
Committee Chair / Thesis Advisor	Nic Vega , Emory University
Committee Members	Daniel Weissman, Emory University Nicole Gerardo, Emory University

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