MPI für Evolutionsbiologie / Evolutionary ecology |
|Host parasite interactions in a cestode with a complex life cycle, Schistocephalus solidus|
|Date of Approval (YYYY-MM-DD):||2006-02-06|
|Name of University:||Christian-Albrechts-Universität|
|Place of University:||Kiel|
(e.g. Total Number of Pages):
|Table of Contents:||Contents
Host parasite interactions 7
Host parasite interactions in complex life cycles 8
Increased transmission through host manipulation 10
Some basics about parasite recognition by host defence systems 11
Schistocephalus solidus, a parasite with a complex life cycle 14
Thesis outline 17
I Copepod activity varies in the course of a parasite infection 20
II Colourful copepods: do parasites manipulate carotenoids? 33
III Fast food or fast lane: tapeworms on their way through 53
the gastro-intestinal tract
IV Surface carbohydrate composition of a tapeworm in its consecutive 69
intermediate hosts: Individual variation and fitness consequences
Published in International Journal for Parasitology 35: 1499-1507 (2005)
V Evolutionary implications of the adaptation to different 87
immune systems in a parasite with a complex life cycle
Published in Proceedings of the Royal Society of London B 272: 2511-2518 (2005)
Curriculum vitae 128
|Abstract / Description:||SUMMARY
Many parasites have complex life cycles, i.e. they have to pass through several host
species to reach maturity. Hence complex life cycles often consist of invertebrate and
vertebrate hosts, the parasite likely varies in the machinery required for infection,
exploitation and transmission of each host. Does the ability to optimally exploit one
host inevitably lead to a reduced ability for the parasite to exploit another host in its
life cycle? To answer this question, I analysed parasite life history traits like
transmission, infection, and establishment in the model system of the tapeworm
Schistocephalus solidus in relation to its two intermediate hosts, a cyclopoid
copepod, and the three-spined stickleback. In this thesis, I particularly focus on
interactions with the hosts’ immune systems and on constraints, which are potentially
shaping the evolution of virulence in parasites with complex life cycles.
The first difficulty for a parasite in a complex life cycle, compared to a single host
system, is to successfully manage the additional transmission steps between hosts.
Orally transmitted parasites often depend on predation of the current host by the next
host. Therefore, to enhance transmission probability, parasites would profit from
increased conspicuousness of the current host, at the time when the parasite is
ready for transmission to the next host. In this thesis I detected that with S. solidus,
infected copepods became more active and that they stored higher amounts of
orange carotenoid droplets. They thus increased in conspicuousness when the
parasite was ready for transmission to the visually hunting three-spined stickleback
(chapter I and II).
After a parasite successfully found and orally entered the next host, an important
step is the penetration of the intestinal mucosal wall. Individuals of S. solidus are
eaten within copepods by its second intermediate host, the three-spined stickleback,
and subsequently penetrate the anterior part of the midgut within 14 to 24 hours.
Contrary to previous assumptions, I found that the outer body layer of S. solidus,
together with the cercomer, is already lost in the stomach of the stickleback so that
the underlying tegument with its microtriches is exposed. This most probably plays
an important role in migration into the body cavity (chapter III).
In each host, parasites have to survive the encounter with the host’s immune system.
Carbohydrates on the parasite’s surface are relevant to mediate host non-self
recognition and parasite camouflage. Evidence in this thesis suggests that
carbohydrates are also important in S. solidus, hence I found individual tapeworms to
change their surface when switching from the invertebrate to the vertebrate host.
Among individual parasites the variation in surface sugar composition was linked to
parasite fitness parameters in the second intermediate host (chapter IV;
Hammerschmidt & Kurtz 2005b).
If parasites with complex life cycles cope better with one of the different types of host
immune systems, the parasite should perform differently in the other hosts. I found,
that parasite sibships of S. solidus traded off adaptation towards different parts of
their hosts’ immune systems. Sibships that performed better in the invertebrate host
also induced lower levels of activation of innate immune components and were less
virulent in the fish host. Above all, this substantiates the constraint of both hosts’
immune systems on parasite performance and the impact on evolution of virulence in
a parasite with a complex life cycle (chapter V; Hammerschmidt & Kurtz 2005a).
|Affiliations:||MPI für Limnologie/Abt. Evolutionsökologie|
|Relations:||Is Version Of-EDOCID:248856|
Is Version Of-EDOCID:250720
|Identifiers:||URL:http://e-diss.uni-kiel.de/diss_1678/ [ID-No:1] |
|You have privileges to view the following file(s):|
|hammerschmidt.pdf [1,00 Mb] |
The scope and number of records on eDoc is subject
to the collection policies defined by each institute
- see "info" button in the collection browse view.