Studies of local adaptation and ecological determinants of infection in a monarch butterfly-parasite interaction Open Access

Sternberg, Eleanore Delaveleye (2012)

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Selective pressures are spatially heterogeneous and many adaptations are specific to the
local environment. By comparing multiple populations, we can gain unique insights into
how species interact with their environment, and how this ultimately results in adaptation.
Such studies are common in host and parasite species, because the reciprocal and
antagonistic nature of their interaction is thought to frequently result in local adaptation.
As expected, a number of studies have found evidence of local adaptation in host-parasite
system. However there are also a substantial number of studies that have failed to find
such evidence. The numerous studies that fail to find local adaptation suggests that the
interaction between host and parasite genotypes may be insufficient to explain expressed
infection phenotype and ultimately, coevolution. In this dissertation, I have examined
infectivity, virulence, and parasite burden in three populations of monarch butterflies and
their protozoan parasites, to explore how these traits vary between populations and to test
for local adaptation. I have then quantified the effect of environmental factors on host and
parasite fitness in this system. Specifically, I examine the effects of monarch food plant
and the effects of competing parasites. When quantifying host fitness in different
populations and on different food plants, I have distinguished between the ability of a
host to resist infection and the ability to tolerate infection without limiting parasite
transmission. I find that there are large differences between the three study populations
and I also find that infection phenotype is often modulated by environmental variables.
Because the environment has a significant effect on host and parasite fitness, I suggest
that these differences may be explained by differences in the ecologies of the three

populations and I emphasize that future studies of local adaptation should include the
important components of the environment which I have identified in this dissertation.

Table of Contents

Table of Contents

Chapter 1: Introduction

1.1 Local adaptation

1.2 Host-parasite interactions and environmental variability

1.3 Monarch butterflies and Ophryocystis elektroscirrha as a model system

Chapter 2: Patterns of infection and the absence of local adaptation in three
populations of monarch butterflies and a naturally occurring protozoan parasite
2.1 Introduction

2.2 Methods

2.3 Results

2.4 Discussion


Chapter 3: Food plant-derived disease tolerance and resistance in a natural
butterfly-plant-parasite interaction
3.1 Introduction

3.2 Methods

3.3 Host fitness, parasite replication, and food plant species

3.4 Food plant chemistry and host fitness

3.5 Discussion


Chapter 4: A virulent parasite can provide protection against a lethal parasitoid
4.1 Introduction


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