Papers by Manfred Milinski
Experimental Parasitology, 2012
With the present study, a culture system for successive life-cycle stages of the tapeworm Schisto... more With the present study, a culture system for successive life-cycle stages of the tapeworm Schistocephalus solidus was developed and this report documents for the first time, cultivation of the procercoid stage of S. solidus from eggs. Additionally we have transformed procercoids dissected from experimentally infected copepods and cultured procercoids into the early plerocercoid stage in vitro. Observations in the culture suggest that the coracidia can interact with their external environment and need no host specific stimuli, except for the components in the culture medium, for activation and hatching from the embryophore. Increasing the culture medium pH from 7.3 to 8.0 improved escape rates and frequencies of hook contractions, suggesting that the oncosphere may recognize and respond to environmental conditions along the host intestine. Procercoids in the culture did not stop growing indicating that conditions within the copepod may be important to limit growth and to induce transformation to plerocercoids. When procercoids are dissected from copepods and transferred to the culture, the outer tegument layers and cercomer starts to loosen. Comparison of the lectin staining of the loosened outer tegument layers and cercomer in procercoids dissected from copepods confirms that transitions of both, the oncosphere to procercoid and procercoid to plerocercoids, has taken place in the in vitro cultures.
Zeitschrift für Tierpsychologie, 2010
Using three-spined sticklebacks (Gasterosteus aculeatus) as predators and water fleas (Daphnia ma... more Using three-spined sticklebacks (Gasterosteus aculeatus) as predators and water fleas (Daphnia magna) as prey, experiments were conducted to investigate whether different swarm regions were differentially preyed upon. The specific location of a region within the swarm, its density, and the motivational state of the predator all influenced the risk of predation. As stragglers were more often attacked than any portion of a swarm itself, natural selection favours all individual swarm members, although differentially.
The Behaviour of Teleost Fishes, 1986
Teleost fish are frequently in danger of being preyed upon. Predators of many taxa are specialise... more Teleost fish are frequently in danger of being preyed upon. Predators of many taxa are specialised piscivores and there are more of them that attack small fish. Therefore, young fish normally live under a high risk of predation, which decreases as they grow older and bigger. Growing fast is not only a good strategy for escaping the prey spectrum of many predators, but also for increasing reproductive success; bigger teleosts are generally able to produce more numerous offspring than smaller ones because bigger females produce more eggs, and bigger males can defend breeding sites better and have a higher social rank; for example, dominant male threespined sticklebacks (Gasterosteus aculeatus) maintain larger territories and have priority of access to females (Li and Owings 1978). Thus, there is a high selection pressure to feed most efficiently in order to grow quickly.
Behavioural Mechanisms of Food Selection, 1990
It is said that Julius Caesar was able to dictate two different letters to two secretaries almost... more It is said that Julius Caesar was able to dictate two different letters to two secretaries almost simultaneously, switching between letters sentence after sentence. The fact that this anecdote has been passed on to our time suggests that Caesar’s ability is appreciated as an exceptional one. Given that the anecdote is true, modern experimental psychology would tell us that Julius Caesar’s brain must have had a supernormal channel capacity. Normally the nervous system is limited in its ability to process sensory data (= channel capacity) which makes it increasingly difficult to fulfil two different tasks at the same time, as each single task gets harder (Broadbent 1965, Blough 1979).
Nature Climate Change, 2013
The difficulty of avoiding dangerous climate change arises from a tension between group and self-... more The difficulty of avoiding dangerous climate change arises from a tension between group and self-interest 1-3 and is exacerbated by climate change's intergenerational nature 4. The present generation bears the costs of cooperation, whereas future generations accrue the benefits if present cooperation succeeds, or suffer if present cooperation fails. Although temporal discounting has long been known to matter in making individual choices 5 , the extent of temporal discounting is poorly understood in a group setting. We represent the effect of both intra-and intergenerational discounting 4,6,7 through a collective-risk group experiment framed around climate change. Participants could choose to cooperate or to risk losing an additional endowment with a high probability. The rewards of defection were immediate, whereas the rewards of cooperation were delayed by one day, delayed by seven weeks (intragenerational discounting), or delayed by several decades and spread over a much larger number of potential beneficiaries (intergenerational discounting). We find that intergenerational discounting leads to a marked decrease in cooperation; all groups failed to reach the collective target. Intragenerational discounting was weaker by comparison. Our results experimentally confirm that international negotiations to mitigate climate change are unlikely to succeed if individual countries' short-term gains can arise only from defection. Present-day political practice interprets the avoidance of 'dangerous climate change' 8 as allowing no more than 2 • C globalmean warming above pre-industrial conditions, implying that global anthropogenic greenhouse gas emissions must be reduced by 50% of present emissions by the year 2050 9-11. Reducing greenhouse gas emissions requires serious effort, and, as Schelling noted, 'to invest resources now in reduced greenhouse emissions is to transfer consumption from ourselves-whoever 'we' are who are making these sacrifices-for the benefit of people distant in the future' 4. Here we test how groups of human subjects respond to the challenge of avoiding dangerous climate change in a setting that rewards defection immediately and rewards cooperation over three different time horizons to represent intraand intergenerational discounting 6,7. In the 'the tragedy of the commons', the neologism often used for global environmental issues, self-interest undermines common resource management-benefits of defection are individualized whereas costs of defection are shared 1. The tragedy of the commons can be modelled with a public goods game, where each person in a group of participants can invest part or their entire operating
Proceedings of the Royal Society of London. Series B: Biological Sciences, 1997
Two fish that cooperatively inspect a predator may have negotiated the share of the risk that eac... more Two fish that cooperatively inspect a predator may have negotiated the share of the risk that each takes. A test of both the costs of predator inspection dependent on the distance from which the predator is approached and the potential benefits of cooperation was carried out strictly experimentally. We made either singletons or pairs of dead sticklebacks, Gasterosteus aculeatus, approach hungry pike, Esox lucius, by remote control according to an algorithm that mimicked natural inspection. The predation risk of both single inspectors and parallel inspecting pairs increased with closer inspection distances. A member of an inspecting pair had only about half the risk of that of a single inspector. In pairs, a companion diluted the lead fish's risk of being caught, depending on its distance behind the leader. The absolute risk difference between leader and follower was greatest for close inspection distances and decreased further away from the predator. The leader's relative risk increased with its distance ahead of the laggard. However, for a given distance between leader and laggard, the relative risks to the two fish remained similar with distance from the predator. The cost side of the inequalities that define a 'Prisoner's Dilemma' has thus been measured for this system. In a second experiment the 'attack deterrence hypothesis' of predator inspection (i.e. inspection decreases attack probability) was tested. The pike was offered a choice between two sticklebacks, one of which had carried out a predator inspection visit. There was no indication of attack deterrence through predator inspection.
Proceedings of the Royal Society B: Biological Sciences, 2012
Punishment can stabilize costly cooperation and ensure the success of a common project that is th... more Punishment can stabilize costly cooperation and ensure the success of a common project that is threatened by free-riders. Punishment mechanisms can be classified into pool punishment, where the punishment act is carried out by a paid third party, (e.g. a police system or a sheriff), and peer punishment, where the punishment act is carried out by peers. Which punishment mechanism is preferred when both are concurrently available within a society? In an economic experiment, we show that the majority of subjects choose pool punishment, despite being costly even in the absence of defectors, when second-order free-riders, cooperators that do not punish, are also punished. Pool punishers are mutually enforcing their support for the punishment organization, stably trapping each other. Our experimental results show how organized punishment could have displaced individual punishment in human societies.
Proceedings of the National Academy of Sciences, 2007
Communication about social topics is abundant in human societies, and many functions have been at... more Communication about social topics is abundant in human societies, and many functions have been attributed to such gossiping. One of these proposed functions is the management of reputations. Reputation by itself has been shown to have a strong influence on cooperation dynamics in games of indirect reciprocity, and this notion helps to explain the observed high level of cooperation in humans. Here we designed a game to test a widespread assumption that gossip functions as a vector for the transmission of social information. This empirical study (with 14 groups of nine students each) focuses on the composition of gossip, information transfer by gossip, and the behavior based on gossip information. We show that gossip has a strong influence on the resulting behavior even when participants have access to the original information (i.e., direct observation) as well as gossip about the same information. Thus, it is evident that gossip has a strong manipulative potential. Furthermore, gossi...
Proceedings of the National Academy of Sciences, 2005
Sexual selection has been proposed as one mechanism to explain the maintenance of high allelic di... more Sexual selection has been proposed as one mechanism to explain the maintenance of high allelic diversity in MHC genes that control the extent of resistance against pathogens and parasites in natural populations. MHC-based sexual selection is known to involve olfactory mechanisms in fish, mice, and humans. During mate choice, females of the three-spined stickleback (Gasterosteus aculeatus) use an odor-based selection strategy to achieve an optimal level of MHC diversity in their offspring, equipping them with optimal resistance toward pathogens and parasites. The molecular mechanism of odor-based mate-selection strategies is unknown. Because peptide ligands for MHC class I molecules function as individuality signals in mice, we hypothesized that female sticklebacks might assess the degree of MHC diversity of potential partners by means of the structural diversity of the corresponding peptide ligands in perceived odor signals. We show that structurally diverse MHC ligands interact wit...
Proceedings of the National Academy of Sciences, 1998
Many problems in human society reflect the inability of selfish parties to cooperate. The “Iterat... more Many problems in human society reflect the inability of selfish parties to cooperate. The “Iterated Prisoner’s Dilemma” has been used widely as a model for the evolution of cooperation in societies. Axelrod’s computer tournaments and the extensive simulations of evolution by Nowak and Sigmund and others have shown that natural selection can favor cooperative strategies in the Prisoner’s Dilemma. Rigorous empirical tests, however, lag behind the progress made by theorists. Clear predictions differ depending on the players’ capacity to remember previous rounds of the game. To test whether humans use the kind of cooperative strategies predicted, we asked students to play the iterated Prisoner’s Dilemma game either continuously or interrupted after each round by a secondary memory task (i.e., playing the game “Memory”) that constrained the students’ working-memory capacity. When playing without interruption, most students used “Pavlovian” strategies, as predicted, for greater memory cap...
Oikos, 1994
I I Opinion is intended to facilitate communication between reader and author and reader and M re... more I I Opinion is intended to facilitate communication between reader and author and reader and M reader. Comments, viewpoints or suggestions arising from published papers are welcome. Discussion and debate about important issues in ecology, e.g. theory or terminology, may also be included. Contributions should be as precise as possible and references should be kept to a 0 P 0 minimum. A summary is not required. 0 N
Nature, 2006
Human cooperation in social dilemmas challenges researchers from various disciplines. Here we com... more Human cooperation in social dilemmas challenges researchers from various disciplines. Here we combine advances in experimental economics and evolutionary biology that separately have shown that costly punishment and reputation formation, respectively, induce cooperation in social dilemmas. The mechanisms of punishment and reputation, however, substantially differ in their means for 'disciplining' non-cooperators. Direct punishment incurs salient costs for both the punisher and the punished, whereas reputation mechanisms discipline by withholding action, immediately saving costs for the 'punisher'. Consequently, costly punishment may become extinct in environments in which effective reputation building-for example, through indirect reciprocity-provides a cheaper and powerful way to sustain cooperation. Unexpectedly, as we show here, punishment is maintained when a combination with reputation building is available, however, at a low level. Costly punishment acts are markedly reduced although not simply substituted by appreciating reputation. Indeed, the remaining punishment acts are concentrated on free-riders, who are most severely punished in the combination. When given a choice, subjects even prefer a combination of reputation building with costly punishment. The interaction between punishment and reputation building boosts cooperative efficiency. Because punishment and reputation building are omnipresent interacting forces in human societies, costly punishing should appear less destructive without losing its deterring force.
Nature, 1987
The problems of achieving mutual cooperation can be formalized in a game called the Prisoner&... more The problems of achieving mutual cooperation can be formalized in a game called the Prisoner's Dilemma in which selfish defection is always more rewarding than cooperation. If the two protagonists have a certain minimum probability of meeting again a strategy called TIT FOR TAT is very successful. In TIT FOR TAT the player cooperates on the first move and thereafter does whatever the opponent did on the previous move. I have studied the behaviour of fish when confronting a potential predator, because conflicts can arise within pairs of fish in these circumstances which I argue resemble a series of games of Prisoner's Dilemma. Using a system of mirrors, single three-spined sticklebacks (Gasterosteus aculeatus) approaching a live predator were provided with either a simulated cooperating companion or a simulated defecting one. In both cases the test fish behaved according to TIT FOR TAT supporting the hypothesis that cooperation can evolve among egoists.
Molecular Ecology, 2009
Polymorphic genes of the major histocompatibility complex (MHC) are regarded as essential genes f... more Polymorphic genes of the major histocompatibility complex (MHC) are regarded as essential genes for individual fitness under conditions of natural and sexual selection. To test this hypothesis, we investigated the ultimate individual fitness trait-that of reproductive success. We used three-spined sticklebacks (Gasterosteus aculeatus) in seminatural enclosures, located in natural breeding areas where the experimental fish had been caught. During their reproductive period, fish were exposed continuously to their natural sympatric parasites. By genotyping almost 4000 eggs with nine microsatellites, we determined parenthood and inferred female mating decision. We found that with reference to their own MHC profile, female sticklebacks preferred to mate with males sharing an intermediate MHC diversity. In addition, males with a specific MHC haplotype were bigger and better at fighting a common parasite (Gyrodactylus sp.). This translated directly into Darwinian fitness since fish harbouring this specific MHC haplotype were more likely to be chosen and had a higher reproductive output. We conclude that females also based their mating decision onaspecificMHChaplotypeconferringresistanceagainstacommonparasite.Thisidentifies and supports 'good genes'. We argue that such an interaction between host and parasite driving assortative mating is not only a prerequisite for negative frequency-dependent selection-a potential mechanism to explain the maintenance of MHC polymorphism, but also potentially speciation.
Molecular Ecology, 2012
Understanding the extent of local adaptation in natural populations and the mechanisms that allow... more Understanding the extent of local adaptation in natural populations and the mechanisms that allow individuals to adapt to their native environment is a major avenue in molecular ecology research. Evidence for the frequent occurrence of diverging ecotypes in species that inhabit multiple ecological habitats is accumulating, but experimental approaches to understanding the biological pathways as well as the underlying genetic mechanisms are still rare. Parasites are invoked as one of the major selective forces driving evolution and are themselves dependent on the ecological conditions in a given habitat. Immunological adaptation to local parasite communities is therefore expected to be a key component of local adaptation in natural populations. Here, we use next-generation sequencing technology to compare the transcriptome-wide response of experimentally infected three-spined sticklebacks from a lake and a river population, which are known to evolve under selection by distinct parasite communities. By comparing overall gene expression levels as well as the activation of functional pathways in response to parasite exposure, we identified potential differences between the two stickleback populations at several levels. Our results suggest locally adapted patterns of gene regulation in response to parasite exposure, which may reflect different local optima in the trade-off between the benefits and the disadvantages of mounting an immune response because of quantitative differences of the local parasite communities.
Journal of Ornithology, 1978
Journal of Evolutionary Biology, 1999
Integrative and Comparative Biology, 2006
Synopsis Mixed-mating, that is reproduction by both self-fertilization and cross-fertilization is... more Synopsis Mixed-mating, that is reproduction by both self-fertilization and cross-fertilization is common in hermaphroditic parasites. Its maintenance poses, however, a problem for evolutionary biology. The tapeworm Schistocephalus solidus Müller 1776, served as a model to study experimentally the consequences of selfing and outcrossing in its 2 consecutive intermediate hosts, a copepod (Macrocyclops albidus Jurine) and the three-spined stickleback fish (Gasterosteus aculeatus). Size-matched tapeworms were allowed to reproduce either alone or in pairs in an in vitro system that replaced the definitive bird host's gut. Selfed eggs from singletons had a 4 times lower hatching success than outcrossed eggs from pairs. Outcrossed offspring achieved both a higher infection success and a higher weight in the copepod, and a higher number of parasites per host in both intermediate hosts, but only under competition. Outcrossed offspring were generally more successful. If a S. solidus plerocercoid has a partner in the bird's gut, they should outcross unless they differ in size and thus cannot solve the Hermaphrodite's Dilemma cooperatively. Using microsatellite markers, the proportion of selfed offspring and the total reproductive output of each worm within pairs varying in mean weight and in weight difference was measured. Worms produced more selfed offspring not only with increasing weight difference as expected but also with decreasing total weight of the pair. If small worms were selfed, they have already purged deleterious mutations and would thus be better selfers in a year with low parasite density when worms cannot find partners. To maintain this advantage they should self a higher proportion of their eggs even with a partner. Here I review recent exprimental evidence.
Evolutionary Ecology, 2006
In parasites with a complex life cycle, the fitness of an individual depends on its probability o... more In parasites with a complex life cycle, the fitness of an individual depends on its probability of reaching the final host and on its fecundity. Because larval growth in intermediate hosts may affect both transmission and adult size, selection should optimize growth patterns that are conditional on the presence and number of conspecific competitors. A recent model predicts that the total parasite volume per host should increase with intensity if larvae are able to vary growth depending on the number of conspecifics in the host (Life History Strategy hypothesis, i.e. LHS). Further, we would here expect growth rates to increase with intensity. By contrast, under the simplest alternative hypothesis of Resource Constraints (i.e. RC), the total parasite volume should remain constant. We experimentally infected copepods Macrocyclops albidus with the cestode Schistocephalus solidus to achieve 1, 2 or 3 parasites per host taking care that hosts had similar quality status at each infection level, and compared larval growth trajectories at the three intensity levels. The asymptotic total parasite volume was larger in double and triple infections than in single infections. Furthermore, the asymptotic total parasite volume was significantly larger in triple than in double infections but only in larger copepods that were less constrained by a host-size ceiling effect. These results, together with the fact that growth rates increased with intensity, support the LHS hypothesis: procercoids of a tapeworm may ''count'' their conspecific competitors in their first intermediate host to harvest its resources strategically until the next step in their complex life cycle.
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Papers by Manfred Milinski