Studies of local adaptation and ecological determinants of infection in a monarch butterfly-parasite interaction Público
Sternberg, Eleanore Delaveleye (2012)
Abstract
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
2
1.2 Host-parasite interactions and environmental variability
7
1.3 Monarch butterflies and Ophryocystis elektroscirrha as a
model system
14
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
19
2.2 Methods
24
2.3 Results
29
2.4 Discussion
35
Chapter 3: Food plant-derived disease tolerance and resistance
in a natural
butterfly-plant-parasite interaction
3.1 Introduction
40
3.2 Methods
43
3.3 Host fitness, parasite replication, and food plant
species
49
3.4 Food plant chemistry and host fitness
52
3.5 Discussion
56
Chapter 4: A virulent parasite can provide protection against a
lethal parasitoid
4.1 Introduction
62
About this Dissertation
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