Cooperation In Public Goods Research Articles

Reputation-based discount effect in imitation on the evolution of cooperation in spatial public goods games

Reputation provides important information to society by recording the historical behavior of individuals. The introduction of reputation helps explain the cooperation phenomenon in human society to some extent. However, in previous explanation models, the benefits of a good reputation bring to individuals are generally described from the perspective of future payoffs they can obtain. In reality, the reputation system also affects the process of mutual imitation among individuals. For instance, the willingness of an individual with a high reputation learning from an individual with a low reputation can be greatly discounted. As such, this paper considers the reputation-based discount effect in imitation and extends the research on reputation from the perspective of imitation learning. Specifically, two situations of discount effect are considered. One is based on relative reputation difference, that is, if the reputation of an individual being imitated is too low compared to the strategy updater and the difference between which exceeds a threshold, the probability of imitation will be discounted. The other is based on absolute reputation difference, that is, if the absolute reputation of an individual being imitated falls below a threshold, the probability of imitation will be discounted. The effect of different thresholds and discount parameters on the evolution of cooperation in spatial public goods games is investigated, respectively, in both situations. Simulation results show that the reputation-based discount effect in mutual imitation plays an important role in the emergence and maintenance of cooperative behavior. Especially, low threshold differences for reputation and high discounts can greatly expand the range of parameters in which cooperation emerges. Moreover, compared with the relative reputation situation, the discount effect based on the absolute reputation is more conducive to the evolution of cooperation.

Group rewarding can promote cooperation and save costs in public goods games

Promoting cooperation in public goods games is a long-standing problem in multiple branches of science. Reward is an effective means of promoting cooperation, but can be costly if distributed on a large scale or over long periods of time. Avoiding excessive costs is naturally of critical concern. We introduce group rewarding into public goods games and explore the impacts of such rewarding on cooperation. Cooperators are rewarded in small groups based on the number of members of cooperative groups and those members’ contributions. We consider a control parameter whose adjustments lead to more cooperation while cutting costs. Simulations performed on square lattice show that group rewarding can cost-effectively lead to higher contributions to the public good. Depending on returns from the public good, which are determined by the value of the synergy factor, rewards can be kept manageable while still promoting cooperation. By running simulations on large lattices, we reveal that our approach is cost-effective even in cases of large populations.

Resource heterogeneity and the evolution of public goods cooperation.

Heterogeneity in resources is a ubiquitous feature of natural landscapes affecting many aspects of biology. However, the effect of environmental heterogeneity on the evolution of cooperation has been less well studied. Here, using a mixture of theory and experiments measuring siderophore production by the bacterium Pseudomonas aeruginosa as a model for public goods based cooperation, we explore the effect of heterogeneity in resource availability. We show that cooperation in metapopulations that were spatially heterogeneous in terms of resources can be maintained at a higher level than in homogeneous metapopulations of the same average resource value. The results can be explained by a positive covariance between fitness of cooperators, population size, and local resource availability, which allowed cooperators to have a disproportionate advantage within the heterogeneous metapopulations. These results suggest that natural environmental variation may help to maintain cooperation.

How much can we learn about voluntary climate action from behavior in public goods games?

Evidence from public goods game experiments holds the promise of informing climate change policies. To fulfill this promise, such evidence needs to demonstrate generalizability to this specific policy context. This paper examines whether and under which conditions behavior in public goods games generalizes to decisions about voluntary climate actions. We observe each participant in two different decision tasks: a real giving task in which contributions are used to directly reduce CO2 emissions and an abstract public goods game. Through treatment variations in this within-subjects design, we explore two factors that are candidates for affecting generalizability: the structural resemblance of contribution incentives between the tasks and the role of the subject pool, students and non-students. Our findings suggest that cooperation in public goods games is only weakly linked to voluntary climate actions and not in a uniform way. For a standard set of parameters, behavior in both tasks is uncorrelated. Greater structural resemblance of the public goods game with the context of climate change mitigation produces more sizable correlations, especially for student subjects.

Multiple learning mechanisms promote cooperation in public goods games with project selection

How evolution favors cooperation is a fundamental issue in social and economic systems. In the business world, actively selecting a suitable project is usually helpful for a businessman to be in an advantageous position. By incorporating project selection mechanism into the threshold public goods game, we have investigated the coupling effect of mutation and imitation in updating one's preferred project scale on the evolution of cooperation. Compared with the situation where there is no project selection mechanism, the existence of project selection may suppress or promote cooperation depending upon different updating rules. There exists a critical ratio of the imitators in the population, below which cooperation is suppressed while above which cooperation is promoted. With the coevolving of individual strategies and preferred project scales, a higher level of cooperation corresponds to a larger average value of the preferred project scales. A theoretical analysis indicates that, as most of the individuals are mutants, the coevolving process is governed by the mutation process, which leads to a smaller average value of the preferred project scales and a lower level of cooperation. As most of the individuals are imitators, the coevolving process is governed by the coupling of the mutation and imitation processes, which leads to a larger average value of the preferred project scales and a higher level of cooperation. As all the individuals are imitators, the coevolving process is governed by the imitation process, which leads to an intermediate average value of the preferred project scales and an intermediate level of cooperation.

Redistribution promotes cooperation in spatial public goods games under aspiration dynamics

Redistribution is an important regulation mechanism commonly used to benefit the whole society by transferring capital to low-income members. How redistribution influences the evolution of cooperation, which has a crucial impact on the sustainable development of society, is studied in this paper. Spatial public goods game models are established and players utilize aspiration dynamics as the updating rule where strategies are chosen by comparing payoffs with an expected aspiration. Both the homogeneous aspiration and heterogeneous aspiration distributions are considered. It is found that redistribution significantly promotes the cooperation. However, with the increase of individual greed, the growth rate of cooperation level has a peak with the increase of redistribution proportion. Furthermore, the effect of redistribution on cooperative promotion under different aspiration distributions varies with the proportion of redistribution. Moreover, the evolutionary results in heterogeneous networks and regular graphs are compared. It is found that the promotion of redistribution for cooperation is more evident in heterogeneous networks, especially when hub nodes have larger aspirations.

Delayed evolutionary model for public goods competition with policing in phenotypically variant bacterial biofilms

The emergence and abundance of public goods cooperation in the face of selfish “cheaters” is an enduring puzzle in the realm of evolutionary biology. The synergistic and antagonistic interactions within and between cooperators and free riders have an immense impact on the sustenance of cooperation, which often maintains biodiversity in nature. We, therefore, address the problem to formulate and theoretically analyze the effects of social interactions on population dynamics of cooperators in a primitive natural population, such as phenotypically variant monospecies pathogenic microbial biofilms, where cooperators often inhibit the defective exploitation of produced goods by active punishment (policing). To make the proposed model more realistic, we introduce two discrete time delays, which are a combined form of quorum sensing delay and the period between secretion and reception of exoenzymes. In the present letter, our primary objectives are to illustrate i) the significance of the policing effect towards the evolutionary stability of cooperation and ii) the impact of delay(s) on the nature of coexistence. We find that the varying costs of policing can divulge four well-known cases, namely, domination of defection, domination of cooperation, bistability, and the stable coexistence of cooperative and defective individuals. Interestingly, the consideration of asymmetric non-zero time delays in receiving the cooperative exoproducts towards kin and non-kin additionally unveils the occurrence of chaotic coexistence between cooperators and free riders which happens through interior crisis.

A graph-based model for public goods with leaderships

So far, research into pubic goods games has been limited to studying the effects of leadership in an experimental works. The results found differ according to the population studied, the number of participants and the country chosen, which makes ideas imprecise when it comes to understanding how cooperation evolves. In this article we try to generalize these works by introducing an agent-based model to simulate interactions in public goods games on a graph, and study the impact of leadership by example on the evolution of cooperation among selfish individuals in a scale-free network. Consistent with recent experimental studies, our results show that leading by example leads to a significant increase in the overall contribution and the group’s welfare, as compared to the situation without leadership. We have demonstrated also that strong leaders have an important role in promoting optimal cooperation in public goods games and consequently they bring more welfare to their groups.

Between-group competition enhances cooperation in resource appropriation games

Cooperation in public goods games increases in the presence of between-group competition. In this study, we validate the effect of between-group competition in a different social dilemma, a resource appropriation game. Unlike the voluntary contributions setting, group performance in this game increases with the exercise of a passive choice: not appropriating units in an open-access resource. We conducted an incentivized experiment using 276 undergraduate students in which groups of four subjects played a resource appropriation game. Different groups within a session were ranked in each round according to the group's aggregate payoff. This ranking determined a group performance multiplier, which increased the payoffs in groups ranked above the median and decreased the payoffs in groups below the median. The multipliers were small enough to keep the individual benefits from appropriation larger than the individual benefits from a higher payoff multiplier (derived from an improvement in group ranking by not appropriating the resource unit). We found that implementing this small group performance multiplier decreased the average appropriation by 31%. This efficiency-enhancing device generated a 19-percentage-point increase in overall earnings in a given session.

Spatial heterogeneity and evolution of fecundity-affecting traits

It is widely recognized that spatial structure in a population has some, and occasionally great, impacts on ecological and evolutionary dynamics. However, it has been observed that in the homogeneous Wright’s island model with a certain standard demographic assumption, spatial structure does not affect the fitness gradient of a fecundity-affecting trait. The location and convergence stability of singular strategies thus remain unchanged. Furthermore, evolutionary branching is impossible for small dispersal rates, and for a wide class of fecundity functions, evolutionary branching is impossible for any dispersal rate if branching does not occur in the corresponding well-mixed model. Spatially homogeneous structure thus often inhibits evolutionary branching. Here we study the impact of spatial heterogeneity on evolutionary dynamics. We consider an infinite Wright’s island model, where different islands have different capacity and fecundity consequences, and therefore the population is spatially heterogeneous. Through the analysis of metapopulation fitness, we derive its first-order and second-order derivatives with respect to mutant’s trait, which are explicitly represented in terms of fecundity derivatives. The selection gradient turns out to be a biased average of local selection pressures in different patch types. We find that evolutionary branching is generally favored in the presence of spatial heterogeneity. We also find a simple condition under which evolutionary branching is particularly favored. Applications to public-goods cooperation and emergent evolutionary branching to cooperators and defectors are discussed.

No effect of intraspecific relatedness on public goods cooperation in a complex community.

Many organisms—notably microbes—are embedded within complex communities where cooperative behaviors in the form of excreted public goods can benefit other species. Under such circumstances, intraspecific interactions are likely to be less important in driving the evolution of cooperation. We first illustrate this idea with a simple theoretical model, showing that relatedness—the extent to which individuals with the same cooperative alleles interact with each other—has a reduced impact on the evolution of cooperation when public goods are shared between species. We test this empirically using strain of Pseudomonas aeruginosa that vary in their production of metal‐chelating siderophores in copper contaminated compost (an interspecific public good). We show that nonsiderophore producers grow poorly relative to producers under high relatedness, but this cost can be alleviated by the presence of the isogenic producer (low relatedness) and/or the compost microbial community. Hence, relatedness can become unimportant when public goods provide interspecific benefits.

Predator-by-Environment Interactions Mediate Bacterial Competition in the Dictyostelium discoideum Microbiome.

Interactions between species and their environment play a key role in the evolution of diverse communities, and numerous studies have emphasized that interactions among microbes and among trophic levels play an important role in maintaining microbial diversity and ecosystem functioning. In this study, we investigate how two of these types of interactions, public goods cooperation through the production of iron scavenging siderophores and predation by the social amoeba Dictyostelium discoideum, mediate competition between two strains of Pseudomonas fluorescens that were co-isolated from D. discoideum. We find that although we are able to generally predict the competitive outcomes between strains based on the presence and absence of either D. discoideum or iron, predator-by-environment interactions result in unexpected competitive outcomes. This suggests that while both cooperation and predation can mediate the competitive abilities and potentially the coexistence of these strains, predicting how combinations of different environments affect even the relatively simple microbiome of D. discoideum remains challenging.

Fast cheater migration stabilizes coexistence in a public goods dilemma on networks

Through the lens of game theory, cooperation is frequently considered an unsustainable strategy: if an entire population is cooperating, each individual can increase its overall fitness by choosing not to cooperate, thereby still receiving all the benefit of its cooperating neighbors while no longer expending its own energy. Observable cooperation in naturally-occurring public goods games is consequently of great interest, as such systems offer insight into both the emergence and sustainability of cooperation. Here we consider a population that obeys a public goods game on a network of discrete regions (that we call colonies), between any two of which individuals are free to migrate. We construct a system of piecewise-smooth ordinary differential equations that couple the within-colony population dynamics and the between-colony migratory dynamics. Through a combination of analytical and numerical methods, we show that if the workers within the population migrate sufficiently fast relative to the cheaters, the network loses stability first through a Hopf bifurcation, then a torus bifurcation, after which one or more colonies collapse. Our results indicate that fast moving cheaters can act to stabilize worker–cheatercoexistence within network that would otherwise collapse. We end with a comparison of our results with the dynamics observed in colonies of the ant species Pristomyrmex punctatus, and argue that they qualitatively agree.

The Prevalence of Conditional Cooperation: A Replication Study in Egypt

There is a prevalent observation in experimental studies that most individuals can be classified as “conditional cooperators” in a public goods game. This study contributes to the existing experimental evidence on the prevalence of conditional cooperation in public goods games regardless of the culture of the subjects. A laboratory experiment replicating Fischbacher et al. (2001) was conducted with Egyptian subjects comparing the percentage of conditional cooperators in Egypt and other countries. Results show that the share of conditional cooperators in the Egyptian subject pool is not significantly different from many other countries with different cultures, which corroborates the prevalence of conditional cooperation.

Microbial expansion-collision dynamics promote cooperation and coexistence on surfaces.

Microbes colonizing a surface often experience colony growth dynamics characterized by an initial phase of spatial clonal expansion followed by collision between neighboring colonies to form potentially genetically heterogeneous boundaries. For species with life cycles consisting of repeated surface colonization and dispersal, these spatially explicit "expansion-collision dynamics" generate periodic transitions between two distinct selective regimes, "expansion competition" and "boundary competition," each one favoring a different growth strategy. We hypothesized that this dynamic could promote stable coexistence of expansion- and boundary-competition specialists by generating time-varying, negative frequency-dependent selection that insulates both types from extinction. We tested this experimentally in budding yeast by competing an exoenzyme secreting "cooperator" strain (expansion-competition specialists) against nonsecreting "defectors" (boundary-competition specialists). As predicted, we observed cooperator-defector coexistence or cooperator dominance with expansion-collision dynamics, but only defector dominance otherwise. Also as predicted, the steady-state frequency of cooperators was determined by colonization density (the average initial cell-cell distance) and cost of cooperation. Lattice-based spatial simulations give good qualitative agreement with experiments, supporting our hypothesis that expansion-collision dynamics with costly public goods production is sufficient to generate stable cooperator-defector coexistence. This mechanism may be important for maintaining public-goods cooperation and conflict in microbial pioneer species living on surfaces.

Group learning versus local learning: Which is prefer for public cooperation?

We study the evolution of cooperation in public goods games on various graphs, focusing on the effects that are brought by different kinds of strategy donors. This highlights a basic feature of a public good game, for which there exists a remarkable difference between the interactive players and the players who are imitated. A player can learn from all the groups where the player is a member or from the typically local nearest neighbors, and the results show that the group learning rules have better performance in promoting cooperation on many networks than the local learning rules. The heterogeneity of networks’ degree may be an effective mechanism for harvesting the cooperation expectation in many cases, however, we find that heterogeneity does not definitely mean the high frequency of cooperators in a population under group learning rules. It was shown that cooperators always hardly evolve whenever the interaction and the replacement do not coincide for evolutionary pairwise dilemmas on graphs, while for PG games we find that breaking the symmetry is conducive to the survival of cooperators.

The path to re-evolve cooperation is constrained in Pseudomonas aeruginosa

BackgroundA common form of cooperation in bacteria is based on the secretion of beneficial metabolites, shareable as public good among cells within a group. Because cooperation can be exploited by “cheating” mutants, which contribute less or nothing to the public good, there has been great interest in understanding the conditions required for cooperation to remain evolutionarily stable. In contrast, much less is known about whether cheats, once fixed in the population, are able to revert back to cooperation when conditions change. Here, we tackle this question by subjecting experimentally evolved cheats of Pseudomonas aeruginosa, partly deficient for the production of the iron-scavenging public good pyoverdine, to conditions previously shown to favor cooperation.ResultsFollowing approximately 200 generations of experimental evolution, we screened 720 evolved clones for changes in their pyoverdine production levels. We found no evidence for the re-evolution of full cooperation, even in environments with increased spatial structure, and reduced costs of public good production – two conditions that have previously been shown to maintain cooperation. In contrast, we observed selection for complete abolishment of pyoverdine production. The patterns of complete trait degradation were likely driven by “cheating on cheats” in unstructured, iron-limited environments where pyoverdine is important for growth, and selection against a maladaptive trait in iron-rich environments where pyoverdine is superfluous.ConclusionsOur study shows that the path to re-evolve public-goods cooperation can be constrained. While a limitation of the number of mutational targets potentially leading to reversion might be one reason for the observed pattern, an alternative explanation is that the selective conditions required for revertants to spread from rarity are much more stringent than those needed to maintain cooperation.

Rigorous or tolerant: The effect of different reputation attitudes in complex networks

In the collaborative network environment, the ubiquitous cooperation phenomenon among autonomous and selfish individuals has drawn extensive attentions during the last years. The evolution of spatial public goods game has provided an important theoretical framework to understand the emergence of cooperation in this field. Along this line, reputation-based mechanisms have been verified to promote in public goods games by taking into consideration the historical behaviors of players. In most existing studies, individuals are assumed to participate in the favorable games (with good reputation partners) to get more payoffs, and they try to avoid interacting with individuals with bad reputation. However, the effect of individuals’ reputation tolerance on the evolution of cooperation in a complex network is still ambiguous. In this paper, we focus on the evolution of cooperation in public goods games on complex networks where individuals may have various reputation tolerances. Specifically, an individual decides whether or not to participate in a public goods game by considering the reputation of its neighbors. The results show that the reputation tolerance based scheme does help to prevent defectors’ free-riding behavior, and enhances the formation of cooperative clusters. Moreover, Fermi function performs worse than Best Imitation and Roulette in regular networks and random networks, but better in scale-free networks.

Does Uncertainty Deter Provision of Public Goods?

Nous étudions un jeu de bien public répété avec un horizon fini et connu (sous la forme du mécanisme de contribution volontaire) avec une incertitude complète sur le rendement marginal du bien public : ni le rendement marginal personnel, ni les rendements marginaux des autres joueurs ne sont connus au moment de la prise de décision sur la contribution individuelle au bien public. Nous montrons que les contributions sont similaires lorsque le rendement marginal du bien public est prédéterminé et parfaitement connu, et lorsqu’il est incertain. Dans les deux cas, les contributions ont tendance à décroître avec la répétition. En tenant compte des résultats expérimentaux précédents, nos résultats suggèrent que la coopération dans les jeux de biens publics est sensible à la source d’incertitude sur le rendement marginal du bien public.

The physical boundaries of public goods cooperation between surface-attached bacterial cells.

Bacteria secrete a variety of compounds important for nutrient scavenging, competition mediation and infection establishment. While there is a general consensus that secreted compounds can be shared and therefore have social consequences for the bacterial collective, we know little about the physical limits of such bacterial social interactions. Here, we address this issue by studying the sharing of iron-scavenging siderophores between surface-attached microcolonies of the bacterium Pseudomonas aeruginosa Using single-cell fluorescence microscopy, we show that siderophores, secreted by producers, quickly reach non-producers within a range of 100 µm, and significantly boost their fitness. Producers in turn respond to variation in sharing efficiency by adjusting their pyoverdine investment levels. These social effects wane with larger cell-to-cell distances and on hard surfaces. Thus, our findings reveal the boundaries of compound sharing, and show that sharing is particularly relevant between nearby yet physically separated bacteria on soft surfaces, matching realistic natural conditions such as those encountered in soft tissue infections.