Responses of Fluctuating Biological Systems

A linear relationship between responses of biological systems and their fluctuations is presented. The fluctuation is given by the variance of a given quantity, whereas the response is given as the average change in the quantity for a given parameter change. By studying experimental evolution where fluorescence per E.coli cell increased, we confirmed our relationship with a positive correlation between the evolutionary rate of fluorescence and its fluctuation observed over genetically identical cells. The generality of the relationship and its possible application to other fluctuating systems are discussed.

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