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Rapid evolution of cooperation in group-living animals.

Franz M, Schülke O, Ostner J - BMC Evol. Biol. (2013)

Bottom Line: In contrast, at low frequencies of cooperators rapid evolutionary dynamics lead to a decrease in assortment, which acts against the evolution of cooperation.Rapid evolutionary dynamics can emerge in this case because sufficiently strong selective pressures allow evolutionary and demographic dynamics, and consequently also feedback between assortment and evolution, to occur on the same timescale.In particular, emerging positive frequency-dependent selection could be an important explanation for differences in cooperative behaviors among different species with similar population structures such as humans and chimpanzees.

View Article: PubMed Central - HTML - PubMed

Affiliation: Courant Research Center Evolution of Social Behavior, University of Göttingen, Kellnerweg 6, Göttingen 37077, Germany. mathias.franz@duke.edu.

ABSTRACT

Background: It is often assumed that evolution takes place on very large timescales. Countering this assumption, rapid evolutionary dynamics are increasingly documented in biological systems, e.g. in the context of predator-prey interactions, species coexistence and invasion. It has also been shown that rapid evolution can facilitate the evolution of cooperation. In this context often evolutionary dynamics influence population dynamics, but in spatial models rapid evolutionary dynamics also emerge with constant population sizes. Currently it is not clear how well these spatial models apply to species in which individuals are not embedded in fixed spatial structures. To address this issue we employ an agent-based model of group living individuals. We investigate how positive assortment between cooperators and defectors and pay-off differences between cooperators and defectors depend on the occurrence of evolutionary dynamics.

Results: We find that positive assortment and pay-off differences between cooperators and defectors differ when comparing scenarios with and without selection, which indicates that rapid evolutionary dynamics are occurring in the selection scenarios. Specifically, rapid evolution occurs because changes in positive assortment feed back on evolutionary dynamics, which crucially impacts the evolution of cooperation. At high frequencies of cooperators these feedback dynamics increase positive assortment facilitating the evolution of cooperation. In contrast, at low frequencies of cooperators rapid evolutionary dynamics lead to a decrease in assortment, which acts against the evolution of cooperation. The contrasting dynamics at low and high frequencies of cooperators create positive frequency-dependent selection.

Conclusions: Rapid evolutionary dynamics can influence the evolution of cooperation in group-living species and lead to positive frequency-dependent selection even if population size and maximum group-size are not affected by evolutionary dynamics. Rapid evolutionary dynamics can emerge in this case because sufficiently strong selective pressures allow evolutionary and demographic dynamics, and consequently also feedback between assortment and evolution, to occur on the same timescale. In particular, emerging positive frequency-dependent selection could be an important explanation for differences in cooperative behaviors among different species with similar population structures such as humans and chimpanzees.

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Illustration of within-group and between-group selection in absence and presence of selection. In all scenarios we assumed a population that consists of 10 groups of 10 individuals. For within-group selection (a, b) we varied the proportion of cooperators within groups while assuming that all groups have the same proportion of cooperators. For between-group selection (c, d) each groups contained either only cooperators or only defectors and we varied the proportion of cooperator groups. In (a) and (c) we assumed that a single individual reproduces and calculated the fitness-dependent probability that the reproducing individual is a cooperator. In (b) and (d) we assumed that a single individual dies and calculated the fitness-dependent probability that the dying individual is a cooperator. In all cases we assumed costs of 1, and benefits of 2. Circles show results in absence of selection (s = 0). Squares show results in presence of selection (s = 0.5).
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Figure 3: Illustration of within-group and between-group selection in absence and presence of selection. In all scenarios we assumed a population that consists of 10 groups of 10 individuals. For within-group selection (a, b) we varied the proportion of cooperators within groups while assuming that all groups have the same proportion of cooperators. For between-group selection (c, d) each groups contained either only cooperators or only defectors and we varied the proportion of cooperator groups. In (a) and (c) we assumed that a single individual reproduces and calculated the fitness-dependent probability that the reproducing individual is a cooperator. In (b) and (d) we assumed that a single individual dies and calculated the fitness-dependent probability that the dying individual is a cooperator. In all cases we assumed costs of 1, and benefits of 2. Circles show results in absence of selection (s = 0). Squares show results in presence of selection (s = 0.5).

Mentions: Changes in assortment that occurred due to the presence of selection indicate the existence of rapid evolutionary dynamics. Greater positive assortment can be achieved by rapid evolution because in mixed groups that contain cooperators and defectors, cooperators have higher death and lower reproduction rates than defectors. As shown in Figure 3, in absence of selection, reproduction and death processes occur according to the random expectation where cooperators and defectors do not differ in reproduction and death rates. In presence of selection, changes in reproduction and death probabilities favor defectors in within-group selection and cooperators in between-group selection (Figure 3). For the assumed coefficient of selection (s = 0.5), changes in reproduction and death probabilities are rather small, which allows substantial influence of stochasticity. Nevertheless, in selection scenarios the frequency of defectors tends to increase in mixed groups. At the same time, groups with many cooperators tend to increase in size and fission at a faster rate compared to groups with few cooperators. These two processes counteract the mixing process that emerges from migration and thus rapid evolution can increase positive assortment.


Rapid evolution of cooperation in group-living animals.

Franz M, Schülke O, Ostner J - BMC Evol. Biol. (2013)

Illustration of within-group and between-group selection in absence and presence of selection. In all scenarios we assumed a population that consists of 10 groups of 10 individuals. For within-group selection (a, b) we varied the proportion of cooperators within groups while assuming that all groups have the same proportion of cooperators. For between-group selection (c, d) each groups contained either only cooperators or only defectors and we varied the proportion of cooperator groups. In (a) and (c) we assumed that a single individual reproduces and calculated the fitness-dependent probability that the reproducing individual is a cooperator. In (b) and (d) we assumed that a single individual dies and calculated the fitness-dependent probability that the dying individual is a cooperator. In all cases we assumed costs of 1, and benefits of 2. Circles show results in absence of selection (s = 0). Squares show results in presence of selection (s = 0.5).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4231370&req=5

Figure 3: Illustration of within-group and between-group selection in absence and presence of selection. In all scenarios we assumed a population that consists of 10 groups of 10 individuals. For within-group selection (a, b) we varied the proportion of cooperators within groups while assuming that all groups have the same proportion of cooperators. For between-group selection (c, d) each groups contained either only cooperators or only defectors and we varied the proportion of cooperator groups. In (a) and (c) we assumed that a single individual reproduces and calculated the fitness-dependent probability that the reproducing individual is a cooperator. In (b) and (d) we assumed that a single individual dies and calculated the fitness-dependent probability that the dying individual is a cooperator. In all cases we assumed costs of 1, and benefits of 2. Circles show results in absence of selection (s = 0). Squares show results in presence of selection (s = 0.5).
Mentions: Changes in assortment that occurred due to the presence of selection indicate the existence of rapid evolutionary dynamics. Greater positive assortment can be achieved by rapid evolution because in mixed groups that contain cooperators and defectors, cooperators have higher death and lower reproduction rates than defectors. As shown in Figure 3, in absence of selection, reproduction and death processes occur according to the random expectation where cooperators and defectors do not differ in reproduction and death rates. In presence of selection, changes in reproduction and death probabilities favor defectors in within-group selection and cooperators in between-group selection (Figure 3). For the assumed coefficient of selection (s = 0.5), changes in reproduction and death probabilities are rather small, which allows substantial influence of stochasticity. Nevertheless, in selection scenarios the frequency of defectors tends to increase in mixed groups. At the same time, groups with many cooperators tend to increase in size and fission at a faster rate compared to groups with few cooperators. These two processes counteract the mixing process that emerges from migration and thus rapid evolution can increase positive assortment.

Bottom Line: In contrast, at low frequencies of cooperators rapid evolutionary dynamics lead to a decrease in assortment, which acts against the evolution of cooperation.Rapid evolutionary dynamics can emerge in this case because sufficiently strong selective pressures allow evolutionary and demographic dynamics, and consequently also feedback between assortment and evolution, to occur on the same timescale.In particular, emerging positive frequency-dependent selection could be an important explanation for differences in cooperative behaviors among different species with similar population structures such as humans and chimpanzees.

View Article: PubMed Central - HTML - PubMed

Affiliation: Courant Research Center Evolution of Social Behavior, University of Göttingen, Kellnerweg 6, Göttingen 37077, Germany. mathias.franz@duke.edu.

ABSTRACT

Background: It is often assumed that evolution takes place on very large timescales. Countering this assumption, rapid evolutionary dynamics are increasingly documented in biological systems, e.g. in the context of predator-prey interactions, species coexistence and invasion. It has also been shown that rapid evolution can facilitate the evolution of cooperation. In this context often evolutionary dynamics influence population dynamics, but in spatial models rapid evolutionary dynamics also emerge with constant population sizes. Currently it is not clear how well these spatial models apply to species in which individuals are not embedded in fixed spatial structures. To address this issue we employ an agent-based model of group living individuals. We investigate how positive assortment between cooperators and defectors and pay-off differences between cooperators and defectors depend on the occurrence of evolutionary dynamics.

Results: We find that positive assortment and pay-off differences between cooperators and defectors differ when comparing scenarios with and without selection, which indicates that rapid evolutionary dynamics are occurring in the selection scenarios. Specifically, rapid evolution occurs because changes in positive assortment feed back on evolutionary dynamics, which crucially impacts the evolution of cooperation. At high frequencies of cooperators these feedback dynamics increase positive assortment facilitating the evolution of cooperation. In contrast, at low frequencies of cooperators rapid evolutionary dynamics lead to a decrease in assortment, which acts against the evolution of cooperation. The contrasting dynamics at low and high frequencies of cooperators create positive frequency-dependent selection.

Conclusions: Rapid evolutionary dynamics can influence the evolution of cooperation in group-living species and lead to positive frequency-dependent selection even if population size and maximum group-size are not affected by evolutionary dynamics. Rapid evolutionary dynamics can emerge in this case because sufficiently strong selective pressures allow evolutionary and demographic dynamics, and consequently also feedback between assortment and evolution, to occur on the same timescale. In particular, emerging positive frequency-dependent selection could be an important explanation for differences in cooperative behaviors among different species with similar population structures such as humans and chimpanzees.

Show MeSH
Related in: MedlinePlus