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The emergence of complexity and restricted pleiotropy in adapting networks
BACKGROUND: The emergence of organismal complexity has been a difficult subject for researchers because it is not readily amenable to investigation by experimental approaches. Complexity has a myriad of untested definitions and our understanding of its evolution comes primarily from static snapshots...
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Formato: | Online Artículo Texto |
Lenguaje: | English |
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BioMed Central
2011
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3224730/ https://www.ncbi.nlm.nih.gov/pubmed/22059952 http://dx.doi.org/10.1186/1471-2148-11-326 |
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author | Le Nagard, Hervé Chao, Lin Tenaillon, Olivier |
author_facet | Le Nagard, Hervé Chao, Lin Tenaillon, Olivier |
author_sort | Le Nagard, Hervé |
collection | PubMed |
description | BACKGROUND: The emergence of organismal complexity has been a difficult subject for researchers because it is not readily amenable to investigation by experimental approaches. Complexity has a myriad of untested definitions and our understanding of its evolution comes primarily from static snapshots gleaned from organisms ranked on an intuitive scale. Fisher's geometric model of adaptation, which defines complexity as the number of phenotypes an organism exposes to natural selection, provides a theoretical framework to study complexity. Yet investigations of this model reveal phenotypic complexity as costly and therefore unlikely to emerge. RESULTS: We have developed a computational approach to study the emergence of complexity by subjecting neural networks to adaptive evolution in environments exacting different levels of demands. We monitored complexity by a variety of metrics. Top down metrics derived from Fisher's geometric model correlated better with the environmental demands than bottom up ones such as network size. Phenotypic complexity was found to increase towards an environment-dependent level through the emergence of restricted pleiotropy. Such pleiotropy, which confined the action of mutations to only a subset of traits, better tuned phenotypes in challenging environments. However, restricted pleiotropy also came at a cost in the form of a higher genetic load, as it required the maintenance by natural selection of more independent traits. Consequently, networks of different sizes converged in complexity when facing similar environment. CONCLUSIONS: Phenotypic complexity evolved as a function of the demands of the selective pressures, rather than the physical properties of the network architecture, such as functional size. Our results show that complexity may be more predictable, and understandable, if analyzed from the perspective of the integrated task the organism performs, rather than the physical architecture used to accomplish such tasks. Thus, top down metrics emphasizing selection may be better for describing biological complexity than bottom up ones representing size and other physical attributes. |
format | Online Article Text |
id | pubmed-3224730 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2011 |
publisher | BioMed Central |
record_format | MEDLINE/PubMed |
spelling | pubmed-32247302011-11-30 The emergence of complexity and restricted pleiotropy in adapting networks Le Nagard, Hervé Chao, Lin Tenaillon, Olivier BMC Evol Biol Research Article BACKGROUND: The emergence of organismal complexity has been a difficult subject for researchers because it is not readily amenable to investigation by experimental approaches. Complexity has a myriad of untested definitions and our understanding of its evolution comes primarily from static snapshots gleaned from organisms ranked on an intuitive scale. Fisher's geometric model of adaptation, which defines complexity as the number of phenotypes an organism exposes to natural selection, provides a theoretical framework to study complexity. Yet investigations of this model reveal phenotypic complexity as costly and therefore unlikely to emerge. RESULTS: We have developed a computational approach to study the emergence of complexity by subjecting neural networks to adaptive evolution in environments exacting different levels of demands. We monitored complexity by a variety of metrics. Top down metrics derived from Fisher's geometric model correlated better with the environmental demands than bottom up ones such as network size. Phenotypic complexity was found to increase towards an environment-dependent level through the emergence of restricted pleiotropy. Such pleiotropy, which confined the action of mutations to only a subset of traits, better tuned phenotypes in challenging environments. However, restricted pleiotropy also came at a cost in the form of a higher genetic load, as it required the maintenance by natural selection of more independent traits. Consequently, networks of different sizes converged in complexity when facing similar environment. CONCLUSIONS: Phenotypic complexity evolved as a function of the demands of the selective pressures, rather than the physical properties of the network architecture, such as functional size. Our results show that complexity may be more predictable, and understandable, if analyzed from the perspective of the integrated task the organism performs, rather than the physical architecture used to accomplish such tasks. Thus, top down metrics emphasizing selection may be better for describing biological complexity than bottom up ones representing size and other physical attributes. BioMed Central 2011-11-07 /pmc/articles/PMC3224730/ /pubmed/22059952 http://dx.doi.org/10.1186/1471-2148-11-326 Text en Copyright ©2011 Le Nagard et al; licensee BioMed Central Ltd. http://creativecommons.org/licenses/by/2.0 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. |
spellingShingle | Research Article Le Nagard, Hervé Chao, Lin Tenaillon, Olivier The emergence of complexity and restricted pleiotropy in adapting networks |
title | The emergence of complexity and restricted pleiotropy in adapting networks |
title_full | The emergence of complexity and restricted pleiotropy in adapting networks |
title_fullStr | The emergence of complexity and restricted pleiotropy in adapting networks |
title_full_unstemmed | The emergence of complexity and restricted pleiotropy in adapting networks |
title_short | The emergence of complexity and restricted pleiotropy in adapting networks |
title_sort | emergence of complexity and restricted pleiotropy in adapting networks |
topic | Research Article |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3224730/ https://www.ncbi.nlm.nih.gov/pubmed/22059952 http://dx.doi.org/10.1186/1471-2148-11-326 |
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