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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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Shortest cycles, their length and crossfeeding. A. For the three selection regimes the mean shortest cycle with standard deviations is plotted through time. Inset panels show the corresponding average bite length on the shortest cycle. In all panels the mean and standard deviation are computed from 25 replicate runs. Using permutation tests, we established all three curves are significantly different (all p < 0.004). B. Number of runs with crossfeeding through time. In short, crossfeeding is present if the shortest cycle cannot be performed by a single group of phenotypically identical individuals, with the group having at least 5 individuals (see Methods).
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Figure 7: Shortest cycles, their length and crossfeeding. A. For the three selection regimes the mean shortest cycle with standard deviations is plotted through time. Inset panels show the corresponding average bite length on the shortest cycle. In all panels the mean and standard deviation are computed from 25 replicate runs. Using permutation tests, we established all three curves are significantly different (all p < 0.004). B. Number of runs with crossfeeding through time. In short, crossfeeding is present if the shortest cycle cannot be performed by a single group of phenotypically identical individuals, with the group having at least 5 individuals (see Methods).

Mentions: As we have shown the core of the ecosystem dynamics was formed by the shortest cycle, we compared these cycles in the different settings. For σ = 0.2 not only bite length, but also cycle length had clearly stagnated (Figure 7A). Translated into bite lengths, a local feedback cycle of length 9 resulted in an average bite of length 7.11, while in the model average bites were 64/6 = 10.7 bits long. Thus on average approximately three bits were processed less if local feedback was present.


Evolution of resource cycling in ecosystems and individuals.

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

Shortest cycles, their length and crossfeeding. A. For the three selection regimes the mean shortest cycle with standard deviations is plotted through time. Inset panels show the corresponding average bite length on the shortest cycle. In all panels the mean and standard deviation are computed from 25 replicate runs. Using permutation tests, we established all three curves are significantly different (all p < 0.004). B. Number of runs with crossfeeding through time. In short, crossfeeding is present if the shortest cycle cannot be performed by a single group of phenotypically identical individuals, with the group having at least 5 individuals (see Methods).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: Shortest cycles, their length and crossfeeding. A. For the three selection regimes the mean shortest cycle with standard deviations is plotted through time. Inset panels show the corresponding average bite length on the shortest cycle. In all panels the mean and standard deviation are computed from 25 replicate runs. Using permutation tests, we established all three curves are significantly different (all p < 0.004). B. Number of runs with crossfeeding through time. In short, crossfeeding is present if the shortest cycle cannot be performed by a single group of phenotypically identical individuals, with the group having at least 5 individuals (see Methods).
Mentions: As we have shown the core of the ecosystem dynamics was formed by the shortest cycle, we compared these cycles in the different settings. For σ = 0.2 not only bite length, but also cycle length had clearly stagnated (Figure 7A). Translated into bite lengths, a local feedback cycle of length 9 resulted in an average bite of length 7.11, while in the model average bites were 64/6 = 10.7 bits long. Thus on average approximately three bits were processed less if local feedback was present.

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