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Biomedical subjects

Manfred Milinski

Publications and source records attributed to Manfred Milinski.

9 recordsLinked to original sources
PubMed2006

MHC genes and oxidative stress in sticklebacks: an immuno-ecological approach.

Individual variation in the susceptibility to infection may result from the varying ability of hosts to specifically recognize different parasite strains. Alternatively, there could be individual host differences in fitness costs of immune defence. Although, these two explanations are not mutually exclusive, they have so far been treated in separate experimental approaches. To analyse potential relationships, we studied body condition and oxidative stress, which may reflect costs of immunity, in three-spined sticklebacks that had been experimentally exposed to three species of naturally occurring parasite. These sticklebacks differed in a trait, which is crucial to specific parasite defence, i.e. individual genetic diversity at major histocompatibility complex (MHC) class IIB loci. Oxidative stress was quantified as tissue acrolein, a technique that has been applied to questions of immuno-ecology for the first time. We measured gene expression at the MHC and other estimates of immune activation. We found that fish with high levels of MHC expression had poor condition and elevated oxidative stress. These results indicate that MHC-based specific immunity is connected with oxidative stress. They could, thus, also be relevant in the broader context of the evolution of sexually selected signals that are based on carotenoids and are, thus supposed to reflect oxidative stress resistance.

Acrolein↗
PubMed2006

Stabilizing the earth's climate is not a losing game: supporting evidence from public goods experiments.

Maintaining the Earth's climate within habitable boundaries is probably the greatest "public goods game" played by humans. However, with >6 billion "players" taking part, the game seems to rule out individual altruistic behavior. Thus, climate protection is a problem of sustaining a public resource that everybody is free to overuse, a "tragedy of the commons" problem that emerges in many social dilemmas. We perform a previously undescribed type of public goods experiment with human subjects contributing to a public pool. In contrast to the standard protocol, here the common pool is not divided among the participants; instead, it is promised that the pool will be invested to encourage people to reduce their fossil fuel use. Our extensive experiments demonstrate that players can behave altruistically to maintain the Earth's climate given the right set of circumstances. We find a nonzero basic level of altruistic behavior, which is enhanced if the players are provided with expert information describing the state of knowledge in climate research. Furthermore, personal investments in climate protection increase substantially if players can invest publicly, thus gaining social reputation. This increase occurs because subjects reward other subjects' contributions to sustaining the climate, thus reinforcing their altruism. Therefore, altruism may convert to net personal benefit and to relaxing the dilemma if the gain in reputation is large enough. Our finding that people reward contributions to sustaining the climate of others is a surprising result. There are obvious ways these unexpected findings can be applied on a large scale.

Journal Article↗
PubMed2005

Mate choice decisions of stickleback females predictably modified by MHC peptide ligands.

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 with natural odors of male sticklebacks to predictably modify MHC-related mate choice. For a mating pair with suboptimal numbers of MHC alleles, peptides increase the attractiveness of male water, whereas for a mating pair with superoptimal numbers, attractiveness is decreased. Our results suggest that female sticklebacks use evolutionarily conserved structural features of MHC peptide ligands to evaluate MHC diversity of their prospective mating partners.

Amino Acid Sequence↗
PubMed2004

Major histocompatibility complex diversity influences parasite resistance and innate immunity in sticklebacks.

Proteins of the major histocompatibility complex (MHC) play a central role in the presentation of antigens to the adaptive immune system. The MHC also influences the odour-based choice of mates in humans and several animal taxa. It has recently been shown that female three-spined sticklebacks (Gasterosteus aculeatus) aim at a moderately high MHC diversity in their offspring when choosing a mate. Do they optimize the immune systems of their offspring? Using three-spined sticklebacks that varied in their individual numbers of MHC class IIB molecules, we tested, experimentally, whether allelic diversity at the MHC influences parasite resistance and immune parameters. We found that sticklebacks with low MHC diversity suffered more from parasite infection after experimental exposure to Schistocephalus solidus tapeworms and Glugea anomala microsporidians. They also showed the highest proportion of granulocytes and the strongest respiratory burst reaction, which are correlates of innate immunity. This indicates a strong activity of the innate immune system after challenge by parasites when MHC diversity is suboptimal. Individuals with very high allelic diversity at the MHC seemed inferior to those with moderately high diversity. Such a pattern is consistent with theoretical expectations of an optimal balance between the number of recognizable antigens and self-tolerance.

Alleles↗
PubMed2003

Volunteering leads to rock-paper-scissors dynamics in a public goods game.

Collective efforts are a trademark of both insect and human societies. They are achieved through relatedness in the former and unknown mechanisms in the latter. The problem of achieving cooperation among non-kin has been described as the 'tragedy of the commons', prophesying the inescapable collapse of many human enterprises. In public goods experiments, initial cooperation usually drops quickly to almost zero. It can be maintained by the opportunity to punish defectors or the need to maintain good reputation. Both schemes require that defectors are identified. Theorists propose that a simple but effective mechanism operates under full anonymity. With optional participation in the public goods game, 'loners' (players who do not join the group), defectors and cooperators will coexist through rock-paper-scissors dynamics. Here we show experimentally that volunteering generates these dynamics in public goods games and that manipulating initial conditions can produce each predicted direction. If, by manipulating displayed decisions, it is pretended that defectors have the highest frequency, loners soon become most frequent, as do cooperators after loners and defectors after cooperators. On average, cooperation is perpetuated at a substantial level.

Cooperative Behavior↗
PubMed2002

Donors to charity gain in both indirect reciprocity and political reputation.

Darwinian evolution can explain human cooperative behaviour among non-kin by either direct or indirect reciprocity. In the latter case one does not expect a return for an altruistic act from the recipient as with direct reciprocity, but from another member of the social group. However, the widespread human behaviour of donating to poor people outside the social group, for example, to charity organizations, that are unlikely to reciprocate indirectly and thus are equivalent to defectors in the game is still an evolutionary puzzle. Here we show experimentally that donations made in public to a well-known relief organization resulted both in increased income (that the donors received from the members of their group) and in enhanced political reputation (they were elected to represent the interests of their group). Donations may thus function as an honest signal for one's social reliability.

Cooperative Behavior↗
PubMed2002

Reputation helps solve the 'tragedy of the commons'.

The problem of sustaining a public resource that everybody is free to overuse-the 'tragedy of the commons'-emerges in many social dilemmas, such as our inability to sustain the global climate. Public goods experiments, which are used to study this type of problem, usually confirm that the collective benefit will not be produced. Because individuals and countries often participate in several social games simultaneously, the interaction of these games may provide a sophisticated way by which to maintain the public resource. Indirect reciprocity, 'give and you shall receive', is built on reputation and can sustain a high level of cooperation, as shown by game theorists. Here we show, through alternating rounds of public goods and indirect reciprocity games, that the need to maintain reputation for indirect reciprocity maintains contributions to the public good at an unexpectedly high level. But if rounds of indirect reciprocation are not expected, then contributions to the public good drop quickly to zero. Alternating the games leads to higher profits for all players. As reputation may be a currency that is valid in many social games, our approach could be used to test social dilemmas for their solubility.

Cooperative Behavior↗
PubMed2002

Outcrossing increases infection success and competitive ability: experimental evidence from a hermaphrodite parasite.

The maintenance of two genetically distinct reproductive modes such as outcrossing and selfing within a population of animals or plants is still a matter of considerable debate. Hermaphroditic parasites often reproduce either alone by selfing or in pairs by outcrossing. They can be used as a model to study potential benefits of outcrossing. Any advantage from outcrossing may be important, especially in host-parasite coevolution, but has not, to our knowledge, been studied yet in any parasite species. We studied the potential effect of outcrossing in a tapeworm, Schistocephalus solidus, on both infection success and growth in its first intermediate host, the copepod Macrocyclops albidus. Tapeworms that had been obtained from natural populations of three-spined sticklebacks (Gasterosteus aculeatus) were allowed to reproduce either alone or in pairs, in an in vitro system that replaced the final host's gut. This resulted in either selfed or outcrossed offspring, respectively. In one part of the experiment, copepods were exposed to either selfed or outcrossed parasites, in a second part to both types simultaneously, in order to study the effect of competition between them. To discriminate parasites of either origin within the same host, a novel method for fluorescent vital labeling was used. We show here for the first time that outcrossed parasites had a higher infection success and faster development in the host. This advantage of outcrossing became apparent only in the competitive situation, in which superior abilities of parasites to extract limiting resources from the host become crucial.

Animals↗