The influence of evolutionary reciprocity and genetic architecture on the evolution of host defense in Caenorhabditis elegans Open Access

Lewis, Jordan (Fall 2022)

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Parasites are ubiquitous in nature and exert intense selection pressure on the populations they infect due to the fitness costs they impose on infected individuals. Consequently, over time host populations tend to evolve defenses to resist or tolerate their parasites. However, the characteristics of the defenses that evolve in host populations are often contextually dependent on the dynamics of their evolutionary interactions. Evolutionary theory and previous empirical research suggest a diverse array of factors can impact the evolution of host defenses. However, direct experimental testing of these predictions has been limited. This dissertation uses experimental evolution in the Caenorhabditis elegansSerratia marcescens host-parasite system to elucidate these questions. In chapter II, I investigated the role of evolutionary reciprocity in shaping the breadth of parasites against which host defenses are effective (defense range). This was done by assaying experimental populations that had been exposed to S. marcescens at one of three levels of reciprocity (dead parasite, one-sided evolution, coevolution) against a range of other S. marcescens strains. In chapter III, I examined the impact of gene flow on adaptation by passaging hosts against parasites for 10 generations and controlling host gene flow and source population. Source populations had different genetic backgrounds (one the same as the sink population and two different) and two evolutionary histories (previously adapted or naïve). This allowed for examining the impact of genetic architecture and evolutionary history. Lastly, in chapter IV I reviewed the history and methodologies of selection experiments and identify the potential advantages of experimental evolution in applied biology. I end by identifying three areas where experimental evolution could assist research and development of industrial products. Overall, this dissertation contributes to a literature that describes the multitude of ways host defenses can be influenced by the dynamics of their interactions with their parasites. It also shows the ways in which the traits that make experimental evolution useful for basic science research can be more effectively used in applied biology.

Table of Contents

Table of Contents


Chapter I: Introduction- 1

Host-Parasite Interactions & the Evolution of Host Defenses- 3

Evolutionary Reciprocity & Coevolution- 4

Genetic Architecture- 5

Experimental Evolution, C. elegans & S. marcescens- 5

Summary of Dissertation Chapters- 7


Chapter II: Antagonistic Coevolution Limits the Range of Host Defense in C. elegans Populations- 9

Introduction- 10

Materials And Methods- 13

Results- 18

Discussion- 21

Supplemental Materials- 26


Chapter III: Gene Flow Accelerates Adaptation to a Parasite- 27


Materials and Methods- 32

Results- 37

Discussion- 41


Chapter IV: The Advantages of Laboratory Natural Selection in the Applied Sciences- 47

Introduction- 48

Why is Laboratory Natural Selection Advantageous for Applied Science?- 54

Past and Current Uses of Laboratory Natural Selection- 61

Past Artificial Selection and Directed Evolution Experiments- 65

Potential Applied Niches for Laboratory Natural Selection - 69

The Future of Laboratory Natural Selection in Applied Studies- 78


Chapter V: Conclusion- 81

Summary and Discussion of Previous Chapters- 81

Evolutionary Reciprocity- 81

Genetic Architecture- 82

Experimental Evolution & its Applications- 83

Future Directions- 84

References- 86

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