Beneficial laggards: multilevel selection, cooperative polymorphism and division of labour in threshold public good games

<p>Abstract</p> <p>Background</p> <p>The origin and stability of cooperation is a hot topic in social and behavioural sciences. A complicated conundrum exists as defectors have an advantage over cooperators, whenever cooperation is costly so consequently, not cooperating pays off. In addition, the discovery that humans and some animal populations, such as lions, are polymorphic, where cooperators and defectors stably live together -- while defectors are not being punished--, is even more puzzling. Here we offer a novel explanation based on a Threshold Public Good Game (PGG) that includes the interaction of individual and group level selection, where individuals can contribute to multiple collective actions, in our model group hunting and group defense.</p> <p>Results</p> <p>Our results show that there are polymorphic equilibria in Threshold PGGs; that multi-level selection does not select for the most cooperators per group but selects those close to the optimum number of cooperators (in terms of the Threshold PGG). In particular for medium cost values division of labour evolves within the group with regard to the two types of cooperative actions (hunting vs. defense). Moreover we show evidence that spatial population structure promotes cooperation in multiple PGGs. We also demonstrate that these results apply for a wide range of non-linear benefit function types.</p> <p>Conclusions</p> <p>We demonstrate that cooperation can be stable in Threshold PGG, even when the proportion of so called free riders is high in the population. A fundamentally new mechanism is proposed how laggards, individuals that have a high tendency to defect during one specific group action can actually contribute to the fitness of the group, by playing part in an optimal resource allocation in Threshold Public Good Games. In general, our results show that acknowledging a multilevel selection process will open up novel explanations for collective actions.</p

Cooperators Unite! Assortative linking promotes cooperation particularly for medium sized associations

<p>Abstract</p> <p>Background</p> <p>Evolution of cooperative behaviour is widely studied in different models where interaction is heterogeneous, although static among individuals. However, in nature individuals can often recognize each other and chose, besides to cooperate or not, to preferentially associate with or to avoid certain individuals.</p> <p>Here we consider a dynamical interaction graph, in contrast to a static one. We propose several rules of rejecting unwanted partners and seeking out new ones, and study the probability of emergence and maintenance of cooperation on these dynamic networks.</p> <p>Results</p> <p>Our simulations reveal that cooperation can evolve and be stable in the population if we introduce preferential linking, even if defectors can perform it too. The fixation of cooperation has higher probability than that of on static graphs, and this effect is more prevalent at high benefit to cost ratios. We also find an optimal number of partners, for which the fixation probability of cooperation shows a maximum.</p> <p>Conclusions</p> <p>The ability to recognize, seek out or avoid interaction partners based on the outcome of past interactions has an important effect on the emergence of cooperation. Observations about the number of partners in natural cooperating groups are in concordance with the result of our model.</p

Evolution of the division of labor between genes and enzymes in the RNA world

The RNA world is a very likely interim stage of the evolution after the first replicators and before the advent of the genetic code and translated proteins. Ribozymes are known to be able to catalyze many reaction types, including cofactor-aided metabolic transformations. In a metabolically complex RNA world early division of labor between genes and enzymes could have evolved, where the ribozymes would have been transcribed from the genes more often than the other way round, benefiting the encapsulating cells through this dosage effect. Here we show, by computer simulations of protocells harboring unlinked RNA replicators that the origin of replicational asymmetry producing more ribozymes from a gene template than gene strands from a ribozyme template is feasible and robust. Enzymatic activities of the two modeled ribozymes are in trade-off with their replication rates, and the relative replication rates compared to those of complementary strands are evolvable traits of the ribozymes. The degree of trade-off is shown to have the strongest effect in favor of the division of labor. Although some asymmetry between gene and enzymatic strands could have evolved even in earlier, surface-bound systems, the shown mechanism in protocells seems inevitable and under strong positive selection. This could have preadapted the genetic system for transcription after the subsequent origin of chromosomes and DNA

Evolution of the division of labor between genes and enzymes in the RNA world

The RNA world is a very likely interim stage of the evolution after the first replicators and before the advent of the genetic code and translated proteins. Ribozymes are known to be able to catalyze many reaction types, including cofactor-aided metabolic transformations. In a metabolically complex RNA world early division of labor between genes and enzymes could have evolved, where the ribozymes would have been transcribed from the genes more often than the other way round, benefiting the encapsulating cells through this dosage effect. Here we show, by computer simulations of protocells harboring unlinked RNA replicators that the origin of replicational asymmetry producing more ribozymes from a gene template than gene strands from a ribozyme template is feasible and robust. Enzymatic activities of the two modeled ribozymes are in trade-off with their replication rates, and the relative replication rates compared to those of complementary strands are evolvable traits of the ribozymes. The degree of trade-off is shown to have the strongest effect in favor of the division of labor. Although some asymmetry between gene and enzymatic strands could have evolved even in earlier, surface-bound systems, the shown mechanism in protocells seems inevitable and under strong positive selection. This could have preadapted the genetic system for transcription after the subsequent origin of chromosomes and DNA

Efficient assembly and long-term stability of defensive microbiomes via private resources and community bistability

Understanding the mechanisms that promote the assembly and maintenance of host-beneficial microbiomes is an open problem. Empirical evidence supports the idea that animal and plant hosts can combine ‘private resources’ with the ecological phenomenon known as ‘community bistability’ to favour some microbial strains over others. We briefly review evidence showing that hosts can: (i) protect the growth of beneficial strains in an isolated habitat, (ii) use antibiotics to suppress non-beneficial, competitor strains, and (iii) provide resources that only beneficial strains are able to translate into an increased rate of growth, reproduction, or antibiotic production. We then demonstrate in a spatially explicit, individual-based model that these three mechanisms act similarly by selectively promoting the initial proliferation of preferred strains, that is, by acting as a private resource. The faster early growth of preferred strains, combined with the phenomenon of ‘community bistability,’ allows those strains to continue to dominate the microbiome even after the private resource is withdrawn or made public. This is because after a beneficial colony reaches a sufficiently large size, it can resist invasion by parasites without further private support from the host. We further explicitly model localized microbial interactions and diffusion dynamics, and we show that an intermediate level of antibiotic diffusion is the most efficient mechanism in promoting preferred strains and that there is a wide range of parameters under which hosts can promote the assembly of a self-sustaining defensive microbiome. This in turn supports the idea that hosts readily evolve to promote host-beneficial defensive microbiomes

The Social and Mental Dynamics of Cooperation = SOCIAL AND MENTAL DYNAMICS OF COOPERATION

Az ESF Eurocores The Evolution of Cooperation and Trading (TECT) programjához kapcsolódó nemzetközi kutatási program keretén belül négy kutatási altémával foglalkoztunk: (1) A nyelv biológiai alapjai és eredete, (2) Akooperáció evolúciójának általános problémái, (3) A replikátor elmélet, és végül (4) A neuronális replikátor hipotézis. A kiemelkedő eredmények rendre a következők: (1) Biological Foundations and Origins of Syntax c. könyv szerkesztése az MIT Press gondozásában; egy, a hierarchikus kifejezés-szerkezet feldolgozására alkalmas, veremmemóriát működtető neuronális modell; Az emberi nyelvkészség és a kooperáció közös eredete, (2) Az erős altruizmus kezdeti elterjedésének lehetőségét megalapozó modell a hasonló egyedek pozitív asszociációja nélkül; A korai evolúcióban az ásványi felszíneken kibontakozó, növekvő komplexitást eredményező szelekciós dinamika vizsgálata (3) A replikátorok újszerű,hierarchikus osztályozása, (4) Annak megmutatása, hogy elvben miként lehetséges a neuronok közötti lokális kapcsolati háló másolása ismert neurális komponens-folyamatok segítségével; dacára annak, hogy az idegsejtek nem szaporodnak. | Within the ESF Eurocores The Evolution of Cooperation and Trading (TECT) we have been doing research on four topics: (1) The biological foundations and origins of language, (2) General problems of the evolution of cooperation, (3) Replicator theory, and (4) The neuronal replicator hypothesis. The most important results obtained in order are: (1) Editing of the book Biologocal Foundations and Origins of Syntax by MIT Press; a neuronal model able to handle inputs conforming to phrase structure grammar; The common origins of human language and cooperation, (2) Inital spread of strong altruism without positive assortment in groups; Dynamics of competing and cooperating molecular replicators on mineral surfaces, (3) A novel, hierarchical classification of replicators, (4) The feasiblilty of neuronal replicators in the brain: connectivity copying of local neuronal groups by known component mechanisms, without the reproduction of neurons

Strategy diversity stabilizes mutualism through investment cycles, phase polymorphism, and spatial bubbles

There is continuing interest in understanding factors that facilitate the evolution and stability of cooperation within and between species. Such interactions will often involve plasticity in investment behavior, in response to the interacting partner's investments. Our aim here is to investigate the evolution and stability of reciprocal invesment behavior in interspecific interactions, a key phenomenon strongly supported by experimental observations. In partcular, we present a comprehensive analysis of a continuous reciprocal investment game between mutualists, both in well-mixed and spatially structured populations, and we demonstrate a series of novel mechanisms for maintaining interspecific mutualism. We demonstrate that mutualistic partners invariably follow investment cycles, during which mutualism firt increases, before both partners eventually reduce their investments to zero, so that these cycles always conclude with full defection. We show that the key mechanism for stabilizing mutualism is phase polymorphism along the investment cycle. Although mutualistic partners perpetually change their strategies, the community-level distribution of investment levels bcomes stationary. In spatially structured populations, the maintenance of polymorphism is further facilitated by dynamic mosaic structures, in which mutualistic partners form expanding and collapsing spatial bubbles or clusters. Additionally, we reveal strategy diversity thresholds, both for well-mixed and spatially structured mutualistic communities, and discuss factors for meeting these thresholds, and thus maintaining mutualism. Our results demonstrate that interspecific mutualism, when considered as plastic investment behavior, can be unstable, and, in agreement with empirical observations, may involve a polymorphism of investment levels, varying both in space and in time. Identifying the mechanisms maintaining such polymorphism, and hence mutualism in natural communities, provides a significant step towards understnding the coevolution and population dynamics of mutualistic interactions

The dynamics of the RNA world : Insights and challenges

The problem of the origin of life is not only one of structure but also that of dynamics. Ever since the seminal result of Manfred Eigen in 1971 showing that early template replication suffers from an error threshold, research has tackled the issue of how early genomes could have been dynamically stable without highly evolved mechanisms such as accurate replication and chromosomes. We review the theory of the origin, maintenance and enhancement of the RNA world as an evolving population of dynamical systems. Investigation of sequence space has revealed how structures are allocated in sequence space and how this affects the nature of the error threshold that sets the selectively maintainable genome length. New applications of old dynamical theory are still possible: the application of Gause’s principle of competitive exclusion, based on resource utilisation, to RNA replication predicts that at most four pairs (plus and minus strands) can stably be maintained on four nucleotides. Other mechanisms of early template coexistence should be regarded as additional means to raise the number of coexisting species above the number set by the competitive exclusion principle. One such example is the hypercycle in which templates were postulated to help replication of the next member in a cycle superimposed on individual replication cycles. Although the hypercycle is ecologically unstable it is evolutionarily unstable because it cannot efficiently compete against emerging parasites. Population structure can modify this conclusion but not without further qualification. The simplest form of population structure is limited diffusion on a surface. This simple mechanism can ensure the coexistence of competing ribozymes contributing to surface metabolism as well as the spread of efficient replicases despite the parasite problem. Hypercycles can only be saved by active compartmentalization when replicators are enclosed in reproducing protocells. Once there are protocells there is no need for internal hypercyclic organization, however. Finally we review two crucial adaptations that enhanced the RNA world: chromosomes and enzymatic metabolism. Interestingly, it was shown that these two have been presumably coevolutionarily linked because protocells harbouring unlinked, competing ribozymes are better off if the ribozymes remain inefficient but generalists. The appearance of chromosomes alleviates intragenomic conflict and is enabling constraint for the emergence of specific and efficient enzymes

The dynamics of the RNA world : Insights and challenges

The problem of the origin of life is not only one of structure but also that of dynamics. Ever since the seminal result of Manfred Eigen in 1971 showing that early template replication suffers from an error threshold, research has tackled the issue of how early genomes could have been dynamically stable without highly evolved mechanisms such as accurate replication and chromosomes. We review the theory of the origin, maintenance and enhancement of the RNA world as an evolving population of dynamical systems. Investigation of sequence space has revealed how structures are allocated in sequence space and how this affects the nature of the error threshold that sets the selectively maintainable genome length. New applications of old dynamical theory are still possible: the application of Gause’s principle of competitive exclusion, based on resource utilisation, to RNA replication predicts that at most four pairs (plus and minus strands) can stably be maintained on four nucleotides. Other mechanisms of early template coexistence should be regarded as additional means to raise the number of coexisting species above the number set by the competitive exclusion principle. One such example is the hypercycle in which templates were postulated to help replication of the next member in a cycle superimposed on individual replication cycles. Although the hypercycle is ecologically unstable it is evolutionarily unstable because it cannot efficiently compete against emerging parasites. Population structure can modify this conclusion but not without further qualification. The simplest form of population structure is limited diffusion on a surface. This simple mechanism can ensure the coexistence of competing ribozymes contributing to surface metabolism as well as the spread of efficient replicases despite the parasite problem. Hypercycles can only be saved by active compartmentalization when replicators are enclosed in reproducing protocells. Once there are protocells there is no need for internal hypercyclic organization, however. Finally we review two crucial adaptations that enhanced the RNA world: chromosomes and enzymatic metabolism. Interestingly, it was shown that these two have been presumably coevolutionarily linked because protocells harbouring unlinked, competing ribozymes are better off if the ribozymes remain inefficient but generalists. The appearance of chromosomes alleviates intragenomic conflict and is enabling constraint for the emergence of specific and efficient enzymes