Evolving Differences: Variation and Diversity in Caenorhabditis elegans Hosts and Their Associated Microbial Communities Restricted; Files Only
Alvarez, Carmen (Spring 2025)
Abstract
Understanding how variance is generated and maintained within biological systems
is central to evolutionary theory. However, despite its importance, variance remains
relatively understudied in dynamic, multi-species systems, like host-microbe systems,
due to the inherent difficulty of quantifying this feature in biologically noisy contexts.
This dissertation investigates how host-microbe associations shape the generation,
persistence, and functional consequences of phenotypic variance across bacterial and
host populations.
In Chapter 1, I show that exposure to a host (Caenorhabditis elegans) led to the
parallel evolution of alternate morphotypes in three bacterial species (Chryseobacterium
gleum, C. indologenes, and Microbacter oxydans). These morphotypes displayed
no apparent fitness advantage except enhanced dispersal via worm-mediated
cuticle carriage, suggesting the evolution of a dispersal-based niche partitioning strategy,
or phoresy. Despite strong directional selection, both original and evolved alternate
morphs coexisted, indicating that host-associated selection can foster stable
phenotypic diversity.
Chapter 2 shifts focus to the host, revealing that C. elegans populations exposed to
virulent Serratia marcescens retained high levels of genetic and phenotypic diversity
over 20 generations, even under strong selective pressure. These results challenge the
expectation of high evolutionary convergence and instead support models in which
host-microbe co-evolution maintains population-level variance.
Chapter 3 presents a microbiology outreach and education activity using agar art
to teach sterile technique. Although methodologically distinct from the experimental
chapters, this work reinforces the central theme of the dissertation by making microbial
variation accessible and emphasizing its relevance through hands-on, creative
learning.
Together, these studies demonstrate that variance can be a repeatable and stable
outcome of eco-evolutionary interactions. By highlighting reciprocal feedbacks
between microbial communities and their hosts, this work contributes to a growing
body of research that understands diversity as a central and functional product of
evolution.
Table of Contents
Table of Contents
1) Introduction: Variation in Host-Microbe Systems.................................1
2) Parallel Evolution of Phoretic Interactions in Microbial Communities
with Caenorhabditis elegans...................................................................7
3) The Effects of Host-Pathogen Evolutionary Relationships on Variation
in Host Mortality...................................................................................25
4) Using Agar Art as a Teaching Tool in the Classroom and Community.....42
5) Conclusion.......................................................................................49
Appendix A Parallel Evolution of Phoretic Interactions in Microbial
Communities with Caenorhabditis elegans.............................................52
Bibliography........................................................................................57
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File download under embargo until 21 August 2026 | 2025-07-15 16:26:36 -0400 | File download under embargo until 21 August 2026 |
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