Evolution of Robustness

Evolution of Robustness Kunihiko Kaneko University of Tokyo, Komaba and ERATO Complex Systems Biology, JST Characterization of biological plasticity, robustness, and evolvability in terms of dynamical systems and statistical analysis is an important issue in Complex Systems Biology.　First, proportionality among evolution speed, phenotypic plasticity, and isogenic phenotypic fluctuation is derived as an extension of fluctuation-response relationship in physics. Following an evolutionary stability hypothesis we then derive a general proportionality relationship between the phenotypic fluctuations of epigenetic and genetic origins; The former is the variance of phenotype due to noise in developmental process, and the latter due to genetic mutation. The relationship suggests a link between robustness to noise and to mutation, as robustness can be defined by the sharpness of the distribution of phenotype. Second, the proportionality between the variances is demonstrated to hold also over different phenotypic traits, when the system acquires robustness through the evolution. The obtained relationships are confirmed in models of gene expression dynamics, as well as in laboratory experiments.　Third, evolutionary restoration of plasticity is investigated both theoretically and experimentally in terms of fluctuations. Compatibility between robustness and plasticity is then discussed. Based on the results, we revisit Waddington’s canalization and genetic assimilation, and discuss how consistency between evolutionary and developmental scales constrains developmental process and leads to universal laws on phenotypic fluctuations. References: K.K. Life: An Introduction to Complex Systems Biology, Springer (2006); PLoS One(2007) 2 e434, J Biosci.34 (2009) 529: Ito et al., Mol. Sys. Biol. 5 (2009) 264

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