Examining the effects of gene flow on host resistance to parasites Open Access

Kandala, Prathyusha (Spring 2021)

Permanent URL: https://etd.library.emory.edu/concern/etds/pc289k19j?locale=en


Incoming gene flow in a population has an important effect on the rate of adaptation in a population. While in some cases the addition of genetic variation through any gene flow is enough to increase the rate of adaptation, the source population of this gene flow can affect how the rate of adaptation changes. For example, a source population possessing certain alleles can increase the focal population’s rate of adaptation more than a different source population with different alleles can. Some populations may even reduce the rate of adaptation due to an influx of deleterious alleles. To understand the impact of gene flow on rapid adaptation, we used obligately outcrossing populations of Caenorhabditis elegans that are capable of evolving resistance to the virulent bacteria, Serratia marcescens, and added gene flow from different populations. We added no gene flow, gene flow from the ancestor C. elegans population, or gene flow from a resistant C. eleganspopulation. While we observed no significant differences in average mortality rate between populations grown in the presence of live S. marcescens that received no gene flow and populations that received ancestor gene flow, the populations that grew with live S. marcescens and that received gene flow from a resistant population had a significantly lower average mortality rate, indicating that adaptation occurred more rapidly in these populations. Furthermore, we saw high average mortality rates in all populations that were grown in the presence of heat-killed S. marcescens, regardless of gene flow status, suggesting that the alleles for resistance are not universally beneficial, and instead only increase in frequency when live S. marcescens is present and able to select for those alleles. Therefore, we see that gene flow can increase the rate of adaptation, but the effects are dependent on the source of the gene flow.

Table of Contents

Introduction 1

Methods 4

Host-Parasite System and Gene Flow Source 4

Experimental Evolution 4

Gene Flow into Population 6

Assessment of Mortality Rates 8

Results 9

Discussion 12

References 15

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