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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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Resource turbulence. For each run, we calculate for all resources the sum of absolute changes in resource abundance through time, and then sum over the resources. Thus we arrive at a single number indicating how turbulent resource dynamics have been through a run. For each selection regime the difference between the local and  model is statistically significant. For σ = 0.2, 1.0 and 5.0 the Wilcoxon rank-sum test (alternative hypothesis: local less than ) results in, respectively, p < 2.73·10-6, p < 5.97·10-8 and p < 1.38·10-12.
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Figure 5: Resource turbulence. For each run, we calculate for all resources the sum of absolute changes in resource abundance through time, and then sum over the resources. Thus we arrive at a single number indicating how turbulent resource dynamics have been through a run. For each selection regime the difference between the local and model is statistically significant. For σ = 0.2, 1.0 and 5.0 the Wilcoxon rank-sum test (alternative hypothesis: local less than ) results in, respectively, p < 2.73·10-6, p < 5.97·10-8 and p < 1.38·10-12.

Mentions: In the comparison between the local and model, resource dynamics in runs with local feedback were less turbulent and more often in equilibrium (Figure 2 and Figure 5). In addition, the local model showed only a minor increase in turbulence from low to high σ, while for the model this increase was much larger (Figure 5). Thus local feedback enhanced a stable cycling of the same resources (i.e. indirect selection for a cycle of resources), which implies fewer mutants established in the populations and therefore a slow down of the evolutionary process.


Evolution of resource cycling in ecosystems and individuals.

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

Resource turbulence. For each run, we calculate for all resources the sum of absolute changes in resource abundance through time, and then sum over the resources. Thus we arrive at a single number indicating how turbulent resource dynamics have been through a run. For each selection regime the difference between the local and  model is statistically significant. For σ = 0.2, 1.0 and 5.0 the Wilcoxon rank-sum test (alternative hypothesis: local less than ) results in, respectively, p < 2.73·10-6, p < 5.97·10-8 and p < 1.38·10-12.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2698886&req=5

Figure 5: Resource turbulence. For each run, we calculate for all resources the sum of absolute changes in resource abundance through time, and then sum over the resources. Thus we arrive at a single number indicating how turbulent resource dynamics have been through a run. For each selection regime the difference between the local and model is statistically significant. For σ = 0.2, 1.0 and 5.0 the Wilcoxon rank-sum test (alternative hypothesis: local less than ) results in, respectively, p < 2.73·10-6, p < 5.97·10-8 and p < 1.38·10-12.
Mentions: In the comparison between the local and model, resource dynamics in runs with local feedback were less turbulent and more often in equilibrium (Figure 2 and Figure 5). In addition, the local model showed only a minor increase in turbulence from low to high σ, while for the model this increase was much larger (Figure 5). Thus local feedback enhanced a stable cycling of the same resources (i.e. indirect selection for a cycle of resources), which implies fewer mutants established in the populations and therefore a slow down of the evolutionary process.

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