The emergence of complexity and restricted pleiotropy in adapting networks

BMC Evolutionary Biology

Research Article

Lin Chao¹  Hervé Le Nagard²  Olivier Tenaillon³ 

[1] Division of Biology, University of California San Diego, La Jolla, California, USA;INSERM, UMR-S 722, F-75018, Paris, France;INSERM, UMR-S 738, F-75018, Paris, France;Univ Paris Diderot, Sorbonne Paris Cité, UMR-S 722 INSERM, F-75018, Paris, France;Univ Paris Diderot, Sorbonne Paris Cité, UMR-S 738 INSERM, F-75018, Paris, France;Institut Claude Bernard, IFR2, F-75018, Paris, France;INSERM, UMR-S 722, F-75018, Paris, France;Univ Paris Diderot, Sorbonne Paris Cité, UMR-S 722 INSERM, F-75018, Paris, France;

关键词: Network Size;    Legendre Polynomial;    High Fitness;    Information Complexity;    Phenotypic Complexity;   

DOI  :  10.1186/1471-2148-11-326

 received in 2011-04-13, accepted in 2011-11-07,  发布年份 2011

来源: Springer

【 摘 要 】

BackgroundThe 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.ResultsWe 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.ConclusionsPhenotypic 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.

【 授权许可】

CC BY   
© Le Nagard et al; licensee BioMed Central Ltd. 2011