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The coevolution of cooperation and dispersal in social groups and its implications for the emergence of multicellularity.

Hochberg ME, Rankin DJ, Taborsky M - BMC Evol. Biol. (2008)

Bottom Line: In addition to the necessity of reducing conflict over effecting specialized tasks, differentiating groups must control the exploitation of the commons, or else be out-competed by more fit groups.The propensity for cheaters to disperse is highest with intermediate benefit:cost ratios of cooperative acts and with high relatedness.We suggest that trait linkage between dispersal and cheating should be operative regardless of whether groups ever achieve higher levels of individuality, because individual selection will always tend to increase exploitation, and stronger group structure will tend to increase overall cooperation through kin selected benefits.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institut des Sciences de l'Evolution, Centre National de Recherche Scientifique, UMR 5554, Université Montpellier II, 34095 Montpellier, France. mhochber@univ-montp2.fr

ABSTRACT

Background: Recent work on the complexity of life highlights the roles played by evolutionary forces at different levels of individuality. One of the central puzzles in explaining transitions in individuality for entities ranging from complex cells, to multicellular organisms and societies, is how different autonomous units relinquish control over their functions to others in the group. In addition to the necessity of reducing conflict over effecting specialized tasks, differentiating groups must control the exploitation of the commons, or else be out-competed by more fit groups.

Results: We propose that two forms of conflict - access to resources within groups and representation in germ line - may be resolved in tandem through individual and group-level selective effects. Specifically, we employ an optimization model to show the conditions under which different within-group social behaviors (cooperators producing a public good or cheaters exploiting the public good) may be selected to disperse, thereby not affecting the commons and functioning as germ line. We find that partial or complete dispersal specialization of cheaters is a general outcome. The propensity for cheaters to disperse is highest with intermediate benefit:cost ratios of cooperative acts and with high relatedness. An examination of a range of real biological systems tends to support our theory, although additional study is required to provide robust tests.

Conclusion: We suggest that trait linkage between dispersal and cheating should be operative regardless of whether groups ever achieve higher levels of individuality, because individual selection will always tend to increase exploitation, and stronger group structure will tend to increase overall cooperation through kin selected benefits. Cheater specialization as dispersers offers simultaneous solutions to the evolution of cooperation in social groups and the origin of specialization of germ and soma in multicellular organisms.

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The fraction of simulations in Model 2 leading to different local optima. Results based on 100 simulations in which initial levels of n, y, and z are each set to a random number between zero and one, inclusive. These simulations produced one of three equilibria: n* = 0, 0 <n* < 1 or n* = 1. Caption a effect of the cost of cooperator dispersal (c) with P = Q = 0.3, s = 0.5, k = 2, e = 0.2; caption b effect of effective group size (k) with P = Q = 0.2, s = 0.6, e = 0.2, c = 0.3.
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Figure 3: The fraction of simulations in Model 2 leading to different local optima. Results based on 100 simulations in which initial levels of n, y, and z are each set to a random number between zero and one, inclusive. These simulations produced one of three equilibria: n* = 0, 0 <n* < 1 or n* = 1. Caption a effect of the cost of cooperator dispersal (c) with P = Q = 0.3, s = 0.5, k = 2, e = 0.2; caption b effect of effective group size (k) with P = Q = 0.2, s = 0.6, e = 0.2, c = 0.3.

Mentions: Permitting social evolution introduces the possibility that the frequency of cooperators or cheaters fixes to zero or one, in which case associations (σ) between dispersal and social strategies are irrelevant. We find that depending on parameter combinations, either only a single global optimum is obtained, or two alternative local optima are possible. In the latter case, which state is obtained depends on initial levels of y, z and n in the numerical simulations. Figure 3 shows the fraction of simulations with random initial levels of n, y and z, achieving either an internal equilibrium (0 <n* < 1), or one with all cooperators (n* = 1), or one with all cheaters (n* = 0) for different costs of cooperator dispersal (c; Fig. 3a) and effective group sizes (k, Fig. 3b). For simplicity in the analyses below, we employ a single arbitrary starting condition (n = y = z = 0.5).


The coevolution of cooperation and dispersal in social groups and its implications for the emergence of multicellularity.

Hochberg ME, Rankin DJ, Taborsky M - BMC Evol. Biol. (2008)

The fraction of simulations in Model 2 leading to different local optima. Results based on 100 simulations in which initial levels of n, y, and z are each set to a random number between zero and one, inclusive. These simulations produced one of three equilibria: n* = 0, 0 <n* < 1 or n* = 1. Caption a effect of the cost of cooperator dispersal (c) with P = Q = 0.3, s = 0.5, k = 2, e = 0.2; caption b effect of effective group size (k) with P = Q = 0.2, s = 0.6, e = 0.2, c = 0.3.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2533331&req=5

Figure 3: The fraction of simulations in Model 2 leading to different local optima. Results based on 100 simulations in which initial levels of n, y, and z are each set to a random number between zero and one, inclusive. These simulations produced one of three equilibria: n* = 0, 0 <n* < 1 or n* = 1. Caption a effect of the cost of cooperator dispersal (c) with P = Q = 0.3, s = 0.5, k = 2, e = 0.2; caption b effect of effective group size (k) with P = Q = 0.2, s = 0.6, e = 0.2, c = 0.3.
Mentions: Permitting social evolution introduces the possibility that the frequency of cooperators or cheaters fixes to zero or one, in which case associations (σ) between dispersal and social strategies are irrelevant. We find that depending on parameter combinations, either only a single global optimum is obtained, or two alternative local optima are possible. In the latter case, which state is obtained depends on initial levels of y, z and n in the numerical simulations. Figure 3 shows the fraction of simulations with random initial levels of n, y and z, achieving either an internal equilibrium (0 <n* < 1), or one with all cooperators (n* = 1), or one with all cheaters (n* = 0) for different costs of cooperator dispersal (c; Fig. 3a) and effective group sizes (k, Fig. 3b). For simplicity in the analyses below, we employ a single arbitrary starting condition (n = y = z = 0.5).

Bottom Line: In addition to the necessity of reducing conflict over effecting specialized tasks, differentiating groups must control the exploitation of the commons, or else be out-competed by more fit groups.The propensity for cheaters to disperse is highest with intermediate benefit:cost ratios of cooperative acts and with high relatedness.We suggest that trait linkage between dispersal and cheating should be operative regardless of whether groups ever achieve higher levels of individuality, because individual selection will always tend to increase exploitation, and stronger group structure will tend to increase overall cooperation through kin selected benefits.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institut des Sciences de l'Evolution, Centre National de Recherche Scientifique, UMR 5554, Université Montpellier II, 34095 Montpellier, France. mhochber@univ-montp2.fr

ABSTRACT

Background: Recent work on the complexity of life highlights the roles played by evolutionary forces at different levels of individuality. One of the central puzzles in explaining transitions in individuality for entities ranging from complex cells, to multicellular organisms and societies, is how different autonomous units relinquish control over their functions to others in the group. In addition to the necessity of reducing conflict over effecting specialized tasks, differentiating groups must control the exploitation of the commons, or else be out-competed by more fit groups.

Results: We propose that two forms of conflict - access to resources within groups and representation in germ line - may be resolved in tandem through individual and group-level selective effects. Specifically, we employ an optimization model to show the conditions under which different within-group social behaviors (cooperators producing a public good or cheaters exploiting the public good) may be selected to disperse, thereby not affecting the commons and functioning as germ line. We find that partial or complete dispersal specialization of cheaters is a general outcome. The propensity for cheaters to disperse is highest with intermediate benefit:cost ratios of cooperative acts and with high relatedness. An examination of a range of real biological systems tends to support our theory, although additional study is required to provide robust tests.

Conclusion: We suggest that trait linkage between dispersal and cheating should be operative regardless of whether groups ever achieve higher levels of individuality, because individual selection will always tend to increase exploitation, and stronger group structure will tend to increase overall cooperation through kin selected benefits. Cheater specialization as dispersers offers simultaneous solutions to the evolution of cooperation in social groups and the origin of specialization of germ and soma in multicellular organisms.

Show MeSH