Assessing the presence of antagonistic fluctuating selection in a non-coevolved host-parasite system Público

Abstract

While the maintenance of outcrossing in nature has puzzled scientists for several decades, the mechanisms that drive this phenomenon are still unclear. Theory posits that Red Queen dynamics in coevolving host-parasite systems lead to parasites imposing antagonistic fluctuating selection on hosts that favors recombination. While previous experiments have shown evidence of antagonistic fluctuating selection in Caenorhabditis elegans populations coevolved with Serratia marcescens, explicit tests had not been performed to determine if this type of selection is unique to coevolving populations. In this study, I performed tests that analyzed whether evidence of antagonistic fluctuating selection was present in C. elegans populations evolved in the presence of changing, non-coevolving S. marcescens strains. While significant host adaptation was noted in these populations, there was a lack of evidence of antagonistic fluctuating selection. In addition, nematodes exposed to non-coevolving, changing parasite strains experienced weaker selection than nematodes coevolved with the parasite. Therefore, it is likely that strong, antagonistic fluctuating selection is a driving force of the maintenance of outcrossing in coevolving host-parasites systems, while weaker directional selection does not select for outcrossing in non-coevolving systems.

Table of Contents

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

Materials and Methods…………………………………………………………………………..6

a)    Survival Assay Protocol………………………………………….....................................10

b)    Statistical Analysis Methods……………………………………………………………..12

Results…………………………………………………………………………………………...13

Discussion……………………………………………………………………………………….15

Figures…………………………………………………………………………………………..19

a)    Figure 1: Caenorhabditis elegans coevolved with Serratia Marcescens experience higher outcrossing rates…………………………………………………………………………19

b)    Figure 2: Phase 1 Protocol Schematic…………………………………………………...20

c)    Figure 3: Phase 2 Protocol Schematic…………………………………………………...20

d)    Figure 4: Caenorhabditis elegans evolved in the presence of changing, non-coevolved Serratia marcescens strains exhibited higher survival rates than the ancestral nematode strain……………………………………………………………………………………...21

e)    Figure 5: Caenorhabditis elegans lineages from the “switch” treatment exhibited higher survival rates than lineages from the coevolved treatment………………………………22

f)     Figure 6: Analyses of genotypes within “switch” treatment population replicates do not provide evidence of antagonistic fluctuating selection…………………………………..23

References……………………………………………………………………………………….24

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School	Emory College
Department	Biology
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Biology, Evolution and Development
Palabra Clave	evolution experimental evolution biology
Committee Chair / Thesis Advisor	Levi Morran, Emory University
Committee Members	Katia Koelle, Emory University Daniel Sinykin, Emory University

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