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Evolution of resource cycling in ecosystems and individuals.

Crombach A, Hogeweg P - BMC Evol. Biol. (2009)

Bottom Line: If individuals are fixed at lattice sites or direct selection is low, indirect selection result in lineages that structure their local environment, leading to 'smart' individuals and stable patterns of resource dynamics.In a baseline model of ecosystem evolution we demonstrate different eco-evolutionary trajectories of resource cycling.By varying the strength of indirect selection through the spatial setting and direct selection, the integration of information by the evolutionary process leads to qualitatively different results from individual smartness to cooperative community structures.

View Article: PubMed Central - HTML - PubMed

Affiliation: Theoretical Biology and Bioinformatics Group, Utrecht University, Utrecht, The Netherlands. anton.crombach@gmail.com

ABSTRACT

Background: Resource cycling is a defining process in the maintenance of the biosphere. Microbial communities, ranging from simple to highly diverse, play a crucial role in this process. Yet the evolutionary adaptation and speciation of micro-organisms have rarely been studied in the context of resource cycling. In this study, our basic questions are how does a community evolve its resource usage and how are resource cycles partitioned?

Results: We design a computational model in which a population of individuals evolves to take up nutrients and excrete waste. The waste of one individual is another's resource. Given a fixed amount of resources, this leads to resource cycles. We find that the shortest cycle dominates the ecological dynamics, and over evolutionary time its length is minimized. Initially a single lineage processes a long cycle of resources, later crossfeeding lineages arise. The evolutionary dynamics that follow are determined by the strength of indirect selection for resource cycling. We study indirect selection by changing the spatial setting and the strength of direct selection. If individuals are fixed at lattice sites or direct selection is low, indirect selection result in lineages that structure their local environment, leading to 'smart' individuals and stable patterns of resource dynamics. The individuals are good at cycling resources themselves and do this with a short cycle. On the other hand, if individuals randomly change position each time step, or direct selection is high, individuals are more prone to crossfeeding: an ecosystem based solution with turbulent resource dynamics, and individuals that are less capable of cycling resources themselves.

Conclusion: In a baseline model of ecosystem evolution we demonstrate different eco-evolutionary trajectories of resource cycling. By varying the strength of indirect selection through the spatial setting and direct selection, the integration of information by the evolutionary process leads to qualitatively different results from individual smartness to cooperative community structures.

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Ecological views of several runs. Each 'wheel' shows the 64 resources (nodes) and the bites (edges) that rotate one resource into another. For visualization purposes even and odd numbered resources are plot on the inner and outer circle, respectively. Resources are colored by abundance, see the legend in panel A. The edge-width is logarithmically scaled according to popularity: the more a bite occurred the thicker the edge. In B, C and D the shortest cycles are colored to distinguish up to 3 different phenotypic groups (orange, purple and green). This coloring does not indicate any relationship between the phenotypes in different 'wheels'. A and C are taken from runs with local feedback (Figure 2A and C), B and D are from runs of the  model (Figure 2J and L). A. Run with low direct selection (σ = 0.2) at time 5·104, which is still in the initial phase of evolution. B. Run with selection σ = 0.2 at time 18·104. The shortest cycle (22, 31, 40, 58) is performed by a single lineage. C. Local model run with σ = 5.0 at time 25·104. The shortest cycle (3, 18, 41, 54) is composed of three different phenotypic lineages. D. Null model run with σ = 5.0 at time 25·104. There several shortest cycles, composed of multiple lineages. One of these cycles is: 4, 12, 24, 40, 49.
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Figure 3: Ecological views of several runs. Each 'wheel' shows the 64 resources (nodes) and the bites (edges) that rotate one resource into another. For visualization purposes even and odd numbered resources are plot on the inner and outer circle, respectively. Resources are colored by abundance, see the legend in panel A. The edge-width is logarithmically scaled according to popularity: the more a bite occurred the thicker the edge. In B, C and D the shortest cycles are colored to distinguish up to 3 different phenotypic groups (orange, purple and green). This coloring does not indicate any relationship between the phenotypes in different 'wheels'. A and C are taken from runs with local feedback (Figure 2A and C), B and D are from runs of the model (Figure 2J and L). A. Run with low direct selection (σ = 0.2) at time 5·104, which is still in the initial phase of evolution. B. Run with selection σ = 0.2 at time 18·104. The shortest cycle (22, 31, 40, 58) is performed by a single lineage. C. Local model run with σ = 5.0 at time 25·104. The shortest cycle (3, 18, 41, 54) is composed of three different phenotypic lineages. D. Null model run with σ = 5.0 at time 25·104. There several shortest cycles, composed of multiple lineages. One of these cycles is: 4, 12, 24, 40, 49.

Mentions: From the runs in Figure 2A, C, J and 2L we have taken a single time point and visualized the ecological interactions between individuals and resources (Figure 3). Again we observe two 'gradients' from rather simple dynamics to complex interwoven cycles of resource modifications: both from local to model, and from low to high direct selection. Moreover, under low direct selection, we find a single lineage performing the resource cycling, while for high selection multiple cooperating lineages are shown.


Evolution of resource cycling in ecosystems and individuals.

Crombach A, Hogeweg P - BMC Evol. Biol. (2009)

Ecological views of several runs. Each 'wheel' shows the 64 resources (nodes) and the bites (edges) that rotate one resource into another. For visualization purposes even and odd numbered resources are plot on the inner and outer circle, respectively. Resources are colored by abundance, see the legend in panel A. The edge-width is logarithmically scaled according to popularity: the more a bite occurred the thicker the edge. In B, C and D the shortest cycles are colored to distinguish up to 3 different phenotypic groups (orange, purple and green). This coloring does not indicate any relationship between the phenotypes in different 'wheels'. A and C are taken from runs with local feedback (Figure 2A and C), B and D are from runs of the  model (Figure 2J and L). A. Run with low direct selection (σ = 0.2) at time 5·104, which is still in the initial phase of evolution. B. Run with selection σ = 0.2 at time 18·104. The shortest cycle (22, 31, 40, 58) is performed by a single lineage. C. Local model run with σ = 5.0 at time 25·104. The shortest cycle (3, 18, 41, 54) is composed of three different phenotypic lineages. D. Null model run with σ = 5.0 at time 25·104. There several shortest cycles, composed of multiple lineages. One of these cycles is: 4, 12, 24, 40, 49.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2698886&req=5

Figure 3: Ecological views of several runs. Each 'wheel' shows the 64 resources (nodes) and the bites (edges) that rotate one resource into another. For visualization purposes even and odd numbered resources are plot on the inner and outer circle, respectively. Resources are colored by abundance, see the legend in panel A. The edge-width is logarithmically scaled according to popularity: the more a bite occurred the thicker the edge. In B, C and D the shortest cycles are colored to distinguish up to 3 different phenotypic groups (orange, purple and green). This coloring does not indicate any relationship between the phenotypes in different 'wheels'. A and C are taken from runs with local feedback (Figure 2A and C), B and D are from runs of the model (Figure 2J and L). A. Run with low direct selection (σ = 0.2) at time 5·104, which is still in the initial phase of evolution. B. Run with selection σ = 0.2 at time 18·104. The shortest cycle (22, 31, 40, 58) is performed by a single lineage. C. Local model run with σ = 5.0 at time 25·104. The shortest cycle (3, 18, 41, 54) is composed of three different phenotypic lineages. D. Null model run with σ = 5.0 at time 25·104. There several shortest cycles, composed of multiple lineages. One of these cycles is: 4, 12, 24, 40, 49.
Mentions: From the runs in Figure 2A, C, J and 2L we have taken a single time point and visualized the ecological interactions between individuals and resources (Figure 3). Again we observe two 'gradients' from rather simple dynamics to complex interwoven cycles of resource modifications: both from local to model, and from low to high direct selection. Moreover, under low direct selection, we find a single lineage performing the resource cycling, while for high selection multiple cooperating lineages are shown.

Bottom Line: If individuals are fixed at lattice sites or direct selection is low, indirect selection result in lineages that structure their local environment, leading to 'smart' individuals and stable patterns of resource dynamics.In a baseline model of ecosystem evolution we demonstrate different eco-evolutionary trajectories of resource cycling.By varying the strength of indirect selection through the spatial setting and direct selection, the integration of information by the evolutionary process leads to qualitatively different results from individual smartness to cooperative community structures.

View Article: PubMed Central - HTML - PubMed

Affiliation: Theoretical Biology and Bioinformatics Group, Utrecht University, Utrecht, The Netherlands. anton.crombach@gmail.com

ABSTRACT

Background: Resource cycling is a defining process in the maintenance of the biosphere. Microbial communities, ranging from simple to highly diverse, play a crucial role in this process. Yet the evolutionary adaptation and speciation of micro-organisms have rarely been studied in the context of resource cycling. In this study, our basic questions are how does a community evolve its resource usage and how are resource cycles partitioned?

Results: We design a computational model in which a population of individuals evolves to take up nutrients and excrete waste. The waste of one individual is another's resource. Given a fixed amount of resources, this leads to resource cycles. We find that the shortest cycle dominates the ecological dynamics, and over evolutionary time its length is minimized. Initially a single lineage processes a long cycle of resources, later crossfeeding lineages arise. The evolutionary dynamics that follow are determined by the strength of indirect selection for resource cycling. We study indirect selection by changing the spatial setting and the strength of direct selection. If individuals are fixed at lattice sites or direct selection is low, indirect selection result in lineages that structure their local environment, leading to 'smart' individuals and stable patterns of resource dynamics. The individuals are good at cycling resources themselves and do this with a short cycle. On the other hand, if individuals randomly change position each time step, or direct selection is high, individuals are more prone to crossfeeding: an ecosystem based solution with turbulent resource dynamics, and individuals that are less capable of cycling resources themselves.

Conclusion: In a baseline model of ecosystem evolution we demonstrate different eco-evolutionary trajectories of resource cycling. By varying the strength of indirect selection through the spatial setting and direct selection, the integration of information by the evolutionary process leads to qualitatively different results from individual smartness to cooperative community structures.

Show MeSH
Related in: MedlinePlus