1,721,096 research outputs found
Climate extreme events and climate change are forced by extortionate free-riders - an economic experiment (dataset)
No full textThis document (xlsx) contains data emerging from an economic experiment conducted in January-February 2023 by Manfred Milinski and Stefania Innocenti
The economic interaction between climate change mitigation, climate migration, and poverty
Full text linkMitigation of anthropogenic climate change takes place against the backdrop of poor countries being most affected by climate change impacts; climate-induced migration is expected to increase in the future. However, the interaction between mitigation, climate migration and poverty has not been investigated explicitly. Here, we represent simultaneous poverty- and climate-induced migration in a laboratory setting, within the collective-risk social dilemma that arises from attempts to avert dangerous climate change. The relatively rich participants try to prevent migration by the relatively poor but in the long run these attempts are unsuccessful because of free-riding among the rich. The rich are willing to increase their effort at averting dangerous climate change when the poor are hit by a climate extreme event exacerbating their poverty. Conversely, the poor are willing to compensate some weaker effort by the rich, as long as the effort by the rich lies above a threshold emerging within the experiment
Consistent Strategy Updating in Spatial and Non-Spatial Behavioral Experiments Does Not Promote Cooperation in Social Networks
Full text linkThe presence of costly cooperation between otherwise selfish actors is not trivial. A prominent mechanism that promotes cooperation is spatial population structure. However, recent experiments with human subjects report substantially lower level of cooperation then predicted by theoretical models. We analyze the data of such an experiment in which a total of 400 players play a Prisoner's Dilemma on a 4 x 4 square lattice in two treatments, either interacting via a fixed square lattice (15 independent groups) or with a population structure changing after each interaction (10 independent groups). We analyze the statistics of individual decisions and infer in which way they can be matched with the typical models of evolutionary game theorists. We find no difference in the strategy updating between the two treatments. However, the strategy updates are distinct from the most popular models which lead to the promotion of cooperation as shown by computer simulations of the strategy updating. This suggests that the promotion of cooperation by population structure is not as straightforward in humans as often envisioned in theoretical models.This work has funding by the German Initiative of Excellence of the German Science Foundation (DFG). J.G.'s work was supported in part by The Ministerio de Ciencia e Innovacion (MICINN) (Spain) through grants PRODIEVO, MOSAICO, FPI, EEBB, and by Comunidad de Madrid (Spain) through grant MODELICO-CM). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Publicad
Reproductive decisions of the tapeworm Schistocephalus solidus
Full text linkIn this thesis the reproductive decisions of S. solidus in the context of mating system evolution, genetic variability and gamete exchange was studied. Microsatellite markers were used to determine if progeny had been reproduced by self- or cross-fertilization. S. solidus individuals reproduce through both selfing and outcrossing even when mating in pairs (i.e. mixed-mating). The usually low densities in their final host force worms sometimes to self-fertilize as last resort. Selfed offspring of worm lineages which have always selfed a certain proportion of their eggs (despite the availability of a partner), may produce fitter progeny than do offspring from worms that have always outcrossed when both have to self in a year of low worm density. The investment in selfing and outcrossing was influenced by mating partner size as well as by partner heterozygosity. Moreover, worms adaptively adjusted their outcrossing rate depending on whether their selfed progeny had a high or a low fitness in terms of hatching rate. This gives them a selective advantage compared to individuals that would outcross and self at random. Genetic variability in a natural population of S. solidus shows a heterozygote deficiency which is in line with the mode of reproduction found in the lab namely mixed-mating. The S. solidus system is to date one of the best established model systems to study mixed-mating in animals in the lab as well as in the field
Investigations on male traits, female mate choice, and the role of parasites in the three-spined stickleback (Gasterosteus aculeatus)
Full text linkMate choice, based on secondary sexual traits is a common phenomenon in many animal species. These traits are exhibited by one of the partners, usually the male. If the traits reflect the ability of a mating partner to contribute direct or indirect benefits to the offspring, individuals (usually females) are able to increase their fitness by choosing these traits. Parasite load and parasite resistance are only two aspects of an animal that can be signalled by such traits. To investigate the effect of parasites and the MHC (Major Histocompatibility Complex) genetic background that is important for parasite resistance, on different male traits, I used the three-spined stickleback (Gasterosteus aculeatus) as a model organism. In most cases, invasion of a host by a parasite is followed by a reaction of the host’s’ immune system. Distinct parasite species have a different impact on their host which might result in different physiological effects. In Chapter I it was shown, in a controlled infection experiment, that two nematode parasites (Camallanus lacustris and Anguillicola crassus) differed in prevalence in their stickleback host. The corresponding immune reaction of the fish was also found to be different, which generally could result in alterations of male traits. The immune reaction of the host does not only depend on parasite species, but also on its own immuno-genetic background. The specific, adaptive immune system in vertebrates is represented by MHC alleles (class I and class IIB). Do male traits also signal direct information about the MHC background of the fish irrespective of parasite load and do females base their mating decision on such traits? In Chapter II two sexually selected male traits, the red breeding colouration and nest quality were correlated to MHC allele number. We found that males with intermediate number of MHC class II alleles built nests that should be more attractive for females, while redness correlated positively with number of MHC I alleles. Visual traits such as red colouration or nest quality seem to reflect parasite resistance of male sticklebacks. Laboratory experiments showed that females also choose mating partners for odour cues that are related to the MHC genetic background. If visual and olfactory cues do not carry the same
information, e.g. different aspects of a males’ condition, this raises the question of female preference in situations where visual and olfactory traits are available at the same time. Through mate choice experiments (Chapter III) it was shown that, in this situation, females seem to use a combination of visual and olfactory traits. While they choose the redder male in the visual test and the best fitting one in the olfactory test, no choice for either the one or the other was found when both choice situations were combined. The females then preferred males for their overall condition, which was not reflected solely by either of the male traits investigated. In order to test whether the results from my laboratory experiments are applicable to the natural situation in the field, outdoor enclosures were stocked with fish of known MHC background (Chapter IV). Parenthood analysis was performed for eggs collected from the males’ nests. Reproductive success was estimated for males and females in combination with measurements of male traits and parasite load. Since it was not possible to identify a certain male trait the females always preferred, choice for a combination of traits also seems most probable in the field.Summary..........................................................................................................2 Zusammenfassung.........................................................................................4 Introduction....................................................................................................6 Sexual selection..........................................................................................6 Multiple sexual traits...................................................................................8 Parasites in sexual selection......................................................................9 The model system.....................................................................................10 Three-spined sticklebacks..............................................................10 Male traits in sticklebacks...............................................................11 Parasites in sticklebacks.................................................................13 Outline...........................................................................................................16 Chapter Ι Infection dose experiment........................................................19Chapter ΙΙ Correlation of MHC to male and female traits.....................37 Chapter ΙΙΙ Laboratory mate choice experiments..................................55 Chapter ΙV Field enclosure experiments..................................................79 Conclusion....................................................................................................98 References..................................................................................................101 Danksagung...............................................................................................114 Curriculum vitae.........................................................................................117 Erklärung......................................................................................................11
Host parasite interactions in a cestode with a complex life cycle, Schistocephalus solidus
Full text linkSUMMARY
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).Contents
Summary 3
Zusammenfassung 5
Introduction
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
Virulence 12
Schistocephalus solidus, a parasite with a complex life cycle 14
Thesis outline 17
Chapters
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)
Conclusion 106
Danksagung 110
References 112
Curriculum vitae 128
Erklärung 13
Hosts and parasites : many ways of interactions ; an approach with two model organisms, the three-spined stickleback (Gasterosteus aculeatus) and its cestode parasite (Schistocephalus solidus)
Full text linkParasites are considered to be one of the major driving forces in the evolution of
organisms. Host-parasite interactions have thus evoked great interest in evolutionary
biology. However, the outcome of an infection might not only be determined by hostparasite
interactions but also by within-host dynamics. Using the three-spined
stickleback (Gasterosteus aculeatus) and the tapeworm Schistocephalus solidus as
model organisms, various aspects of such potential interactions were investigated.
Multiple infections of the stickleback with S. solidus occur frequently in nature and
the specific within-host dynamics might have important consequences for the
outcome of the infection. Interactions between co-infecting S. solidus individuals
could be influenced by the fact that they are likely to be future mating partners in the
final bird host. In a mate choice experiment, we let cestodes choose between a related
(full-sibling) and an unrelated mating partner. To investigate whether the behavioural
preference is reflected in the number of eggs produced with the respective mating
partner, parentage analyses of the offspring were conducted. A second experiment
was carried out to calculate the difference in hatching success between related and
unrelated matings. Despite the 3.5-fold lower hatching rate in incestuous matings, the
cestodes showed a significant preference for their sibling. This was confirmed by the
molecular data: the cestodes produced significantly more eggs with the related than
with the unrelated partner (Chapter I). To investigate potential fitness consequences
for S. solidus in multiple infections, we double infected sticklebacks. Thereby,
relatedness of the parasites and the time between infections were taken into account.
Double infections were established more often when the two parasites were related. In
sequential infections, the secondly acquired parasite was more likely to survive and
grew to a larger size compared to the first one, despite being one week younger. This
difference was not apparent when both parasites were acquired simultaneously
(Chapter II). An earlier in vitro-study suggests that S. solidus is capable of
suppressing innate immune responses of the stickleback. However, little is known
about the adaptive immune response with respect to S. solidus infections. By
repeatedly injecting antigens in vivo, we challenged the adaptive part of the immune
system of S. solidus-exposed and non-exposed sticklebacks. Parameters of innate and
adaptive immunity were measured 9, 13 and 23 weeks post-infection. No adaptive
immune reaction towards S. solidus or the applied antigens was detected. S. solidus
was, however, found to elicit an innate immune response confirming previous studies
(Chapter III). The major histocompatibility complex (MHC) plays a key role in the
specific parasite resistance of vertebrates. In the three-spined stickleback, there is
mounting evidence that an intermediate rather than a maximal individual MHC allele
diversity is favoured. In a correlative study, individual allele diversity of MHC class
IIB as well as MHC class I was related to important fitness traits of the stickleback.
While for male nest quality an optimum concerning MHC class IIB diversity was
found, male breeding colouration was most intense at a maximal MHC class I
diversity. Two MHC class I alleles were identified to be associated with a higher
intensity of red colouration. Moreover, the probability of carrying these alleles
increased with an increasing individual allele diversity, possibly explaining the
positive correlation mentioned above (Chapter IV).Summary 5
Zusammenfassung 7
Introduction
Hosts and parasites 9
The model system
The parasite’s life cycle 10
One host – the three-spined stickleback 11
One parasite – many ‘decisions’
Parasite-host interactions 13
Parasite-parasite interactions 15
Mating decisions 16
Sexual conflict 17
Thesis Outline 18
Chapter I 21
Incestuous mate preference in a simultaneous hermaphrodite
with strong inbreeding depression
Chapter II 35
Multiple infections: Relatedness and time between infections
affect the establishment and growth of the cestode
Schistocephalus solidus in its stickleback host
Chapter III 52
Effects of the cestode Schistocephalus solidus on innate and
adaptive immune traits of the three-spined stickleback
(Gasterosteus aculeatus)
Chapter IV 69
Individual MHC class I and MHC class IIB diversity are
associated with male and female fitness traits in the
three-spined stickleback
Conclusion 85
Danksagung 87
References 89
Curriculum Vitae 105
Erklärung 10
Combining genomics and transcriptomics to study adaptation to lake and river habitats in three-spined sticklebacks
Full text linkUnderstanding the genetic basis of adaptive evolution is a prime objective inmodern evolutionary studies. However, disentangling adaptive and neutralevolution remains a challenging task. Parallel evolution, where similarphenotypes independently arise in similar environments, provides compellingevidence for adaptation, as the repeated emergence of similar phenotypes isunlikely to happen due to neutral processes alone. The three-spined stickleback(Gasterosteus aculeatus) represents an ideal system to study parallel evolutiondue to its rapid adaptation to various freshwater habitats since the last glaciation.The repeated adaptation to lake and river habitats has been proposed to bedriven by distinct parasite environments. This has resulted into distinct lake andriver ecotypes differing in their parasite defense. In this thesis, I investigated themagnitude of genetic parallelism and habitat-specific gene expression underlyingthe repeated phenotypic adaptation to the distinct habitats of lakes and rivers. Inmy first chapter I developed a novel genome scan approach based on mutualinformation criteria. By applying this approach to whole-genome sequencingdata of wild-caught three-spined sticklebacks from five parapatric lake riverpopulation pairs, I detected a low degree of parallel genetic changes across thesegeographically widespread population pairs. In contrast, in my second chapter,transcriptome profiling of two immune tissues from a subset of the individualsused for the genome study discovered habitat-specific gene expression patterns.Such habitat-specific patterns display similar expression among the sameecotypes but different expression between ecotypes, indicating parallelism at theexpression level. I identified a total of 139 genes with habitat-specific expressionpatterns, eight of which were annotated with immune functions and 42differentially expressed in previous parasite exposure experiments, suggestive ofa parasite defense function in nature. Integrating the genome and transcriptomeanalyses from the first two chapters, the last chapter addressed the genetic basisof habitat-specific gene expression. Using genome and transcriptome data fromthe same individual fish, I evaluated the extent of sequence divergence incis-regulatory regions and gene copy number divergence associated withexpression divergence. Though weak correlations were found genome-wide, twogenes showed significant divergence in both gene copy number and geneexpression; the strong correlation between gene copy number and expressionlevel in these two genes suggest a dosage effect impacts habitat-specific geneexpression. Taken together, this thesis provides a detailed view on genetic andtranscription divergence between lake and river sticklebacks, and describes thecomplex and idiosyncratic nature of evolution at the genetic level. Mycontributions support the idea that gene expression promotes repeatedadaptation to lake and river environments, largely influenced by non-parallelmutations, but in some cases facilitated by recurrent copy number changes at thegenetic level.Summary 4 Zusammenfassung 6 Introduction 8 1.1 Adaptive evolution and parallel evolution 8 1.2 Adaptive evolution of gene expression 10 1.3 Genetics of adaptive evolution 13 1.4 The three-spined stickleback as an evolutionary research model 16 Thesis outline 18 Chapter I. Genomic parallelism detection via mutual information 21 Chapter II. Habitat-specific gene expression in sticklebacks 37 Chapter III. Genetics underlying habitat-specific gene expression 65 Conclusion 92 Bibliography 95 Acknowledgements 107 Curriculum Vitæ 109 Declaration 11
Human cooperative behavior
Full text linkSummary
Evolutionary theory provides the biological sciences, with a fundamental and
powerful model to explain the emergence of cooperative behavior. A detailed
explanation for the existence of cooperation between related individuals is provided
by the theory of kin selection. When kin cooperate the helper gives the receiver an
advantage and thereby increases the relative probability that copies of his own
genes are present in the next generations. However, one cannot explain examples of
apparent altruism through kin selection, because in these cases unrelated individuals
interact. The answer for many of these examples is provided by the theory of
reciprocal altruism, where individuals behave reciprocal by returning help to a
previous donor. By applying these two theories it is possible to explain many, but by
far not all cooperative situations. There have to be other mechanisms that lead to
cooperation and sustain already established cooperation.
In my dissertation I have tested empirically new models and predictions of
how cooperation between unrelated humans can be established. This research is
especially important because we interact in a close net of relationships, where
cooperation between unrelated individuals plays one of the main roles. Modern
human societies are impossible to imagine without cooperation between unrelated
individuals. By identifying the circumstances under which cooperation is stable
between unrelated individuals, it will be possible to understand the deciding factors in
politics, economy and in our private lives. As a consequence we would be provided
with intellectual tools to positively influence the deciding factors by alternating the
circumstances accordingly.
We are often not aware of the importance of cooperation between unrelated
partners in our daily lives. Regularly people find unconsciously cooperative solutions,
for instance when they try simultaneously to walk through a narrow door. Some
professions depend very strongly on cooperative behavior between unrelated
colleagues. To act uncooperatively in such a profession can endanger the health or
even the lives of the colleagues (e.g. firemen and firewoman). Cooperative strategies
for these kinds of situations have to have evolved and need to be evolutionary
stable, otherwise we would hardly ever find cooperative behavior in the present and
then only between related individuals. According to the evolutionary theory the
cooperative strategies found today, also have to provide an advantage to the bearer.
For a long time economists and biologists have been interested in the
emergence and sustainability of cooperative behavior. Nevertheless, only with the
introduction of game theory, a mathematical basis was established to incorporate
this behavior into biological evolutionary models. From then on it was possible to
make predictions with the help of theoretical models, about the circumstances under
which certain behavioral patterns emerge and what underlying mechanisms possibly
sustain these patterns.
In my dissertation I have empirically tested predictions of circumstances that
promote cooperative behavior between unrelated humans. The main results of my
work are the following: (i) Humans often donate money to charity. On first sight this
seems to be a disadvantageous behavioral trait. Donations to charity include costs
that reduce the direct fitness of the individual. However, it has to be beneficial to the
bearer, otherwise it would be eliminated from the population through evolutionary
processes. The study showed that there is indeed an advantage. By donating money
to charity (here to UNICEF) one builds up a good personal reputation in the own
social group. Participants that donated to UNICEF received with higher probability
help from other participants and were as well more likely to be voted the group
representative. (ii) Reputation is known to be an important currency in indirect
reciprocity games. Humans therefore should also try to establish a good reputation in
other social games, when this reputation is known in future indirect reciprocity
games. Humans are in general unable to sustain a public resource that everybody is
free to overuse anonymously. Is it possible that humans sustain a public resource if
the use of the resource is linked to the personal reputation? The experiment showed,
that the risk of loosing a good reputation by overusing the public resource actually
lead to sustaining it. Furthermore the public resource was not only sustained, but
also turned out to be surprisingly profitable to all group members. (iii) A theoretical
model supplied a new possibility to sustain a public resource and hereby make
humans act cooperatively. The strikingly simple idea was to introduce the possibility
not to participate in the public goods group and instead use a personal resource with
a low but sure payoff. The prediction was an always recurring rise to dominance, of
three strategies ((a) not to participate in the public goods group, (b) participate in the
public goods group and to cooperate within the group or (c) participate and to defect
within the group) within the population. This dynamic was expected because
whenever most members of the population choose the same strategy, one of the
other two strategies had a higher payoff. The same type as the predicted dynamic
has also been found in models of the famous children game of “rock-paper-scissors”.
The model predicted that the public resource is sustained by the ongoing dynamic,
which is liked with a recurring rise of cooperative behavior. Is it enough to supply
humans with the possibility not to participate in the public goods game to produce
such recurring rise of cooperation? The dynamic was established as predicted,
whereby the changing dominance of the three strategies with repeated cooperative
phases could be observed and the resource was on average sustained. (iv) When
humans make decisions about using a public resource, which at some times are
reputation relevant and at other times are not reputation relevant, do they use this
information strategically? In this study it was shown that, humans are aware when
their decisions are not reputation relevant and immediately reduce their cooperation
to maximize their personal profit. Once more, as soon as the decisions about using
the public resource were linked to the reputation, cooperation was much higher and
the resource was sustained. (v) In some potentially cooperative situations humans’
meet partners from outside the own social group. These “strangers” have a
reputation that they have built in another social group. Do humans put a different
value on a strangers’ reputation in comparison to the reputation of members of the
own social group? It was shown that it is not relevant if the reputation was built within
the own or in a foreign social group.
In summary we found the following: Humans behave uncooperatively, when it
is to the personal advantage. However, certain circumstances lead to cooperative
behavior in humans. Reputation building is one of the most important mechanisms in
this context, which enables us to cooperate even with not related strangers. However
humans consciously make strategic use of situations where they do not harm their
reputation by behaving uncooperatively. Nevertheless, even in completely
anonymous situations it is possible to create circumstances, like introducing optional
participation in the public goods situations, which promote cooperative behavior in
humans.Contents
Summary 7
Zusammenfassung 11
Introduction
1 Cooperation 17
2 Game Theory 18
3 General approach to testing 20
4 Thesis outline 23
Chapters
I Donors to charity gain in both indirect reciprocity and political 29
reputation
II Reputation helps solve the 'tragedy of the commons' 37
III Volunteering leads to rock-paper-scissors dynamics in a public 47
goods game
IV A human cooperation strategy that is conditional on being 59
recognized in other situations
V Reputation is valuable inside and outside the own social group 69
Conclusion 81
Danksagung 83
References 85
Glossary 91
Appendix 93
Curriculum vitae 99
Erklärung 10
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