Evolution of Parasite Avoidance Impacts Investment in Alternative Host Defenses Open Access

Abstract

Host-parasite interactions can lead to a variety of adaptations by both the host and parasite. Host fitness can be elevated through the evolution of beneficial behaviors or physiological responses that inhibit a parasite’s virulence. However, the development of one defense may reduce the selective potential for alternative defenses. In a previous study, experimentally evolved Caenorhabditis elegans populations developed varying degrees of avoidance of the bacterial parasite, Serratia marcescens. Here, I attempted to isolate the effects of innate immune resistance in these same C. elegans populations to determine if the evolution of parasite avoidance traded off the evolution of the immune response. These host populations were exposed to S. marcescens in liquid media, limiting the effects of the evolved avoidance. Host populations that were experimentally evolved with exposure to a coevolving parasite developed increased resistance relative to host populations experimentally evolved without exposure to parasite. Increased resistance could not be detected for host populations experimentally evolved with a fixed parasite, but the host-mortality was much lower in these liquid media assays than what is observed on solid media. Further analysis is required to adequately assess these experimental host populations’ innate immune response to their ancestral bacterial parasite, but with this analysis there is evidence for the evolution of distinct host defenses for at least a subset of the experimentally evolved populations.

Table of Contents

Introduction………………………………………………………………………………………1

Methods…………………………………………………………………………………………..5

·      Establishment and Maintenance of C. elegans host populations with range in host defenses

·      S. marcescens parasite strain

·      Assessment of Parasite Avoidance: Bacterial Choice Index

·      Preparation of C. elegans for Liquid Media Mortality Assays

§ Figure 1

o  Synchronization

o  Gut Treatment

o  Biosorter Preparation

·      Preparation of S. marcescens for Liquid Media Mortality Assays

o  Inoculation

o  Transfer to S-medium

o  Dosage

·      Preparation of E. coli for Liquid Media Mortality Assays

o  Inoculation

o  Transfer to S-medium

·      Dosage Response Assay

·      Liquid Media Mortality Assay

·      Statistical Analysis

Results………………………………………………………………………………….………...12

·      Dosage-Response Assay

§ Figure 2A

§ Figure 2B

·      Liquid Media Mortality Assay

o  Effects of Evolutionary Treatment on Mortality in Liquid Media

§ Figure 3

Discussion………………………………………………………………………………………..14

References…………………………………………………………………….………………….17

About this Honors Thesis

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School	Emory College
Department	Biology
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Biology, Parasitology Biology, Ecology Biology, Evolution and Development
Keyword	Host defense Evolution Host-Parasite
Committee Chair / Thesis Advisor	Levi Morran, Emory University
Committee Members	Jacobus de Roode, Emory University Jeremy Weaver, Emory University

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