Experimental Study of Adaptation to the Edge of Chaos and Critical Scaling in the Self-adjusting Peroxidase-Oxidase Reaction

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

0140179 Hubler One aspect of biocomplexity is the ability of biota to self-adjust to their environment. Previous studies of adaptive behavior have shown that adaptive systems will evolve over time to states that are weakly chaotic, a condition known as the edge of chaos. These studies typically use a genetic algorithm (computer-based evolution) to implement adaptation. It is conjectured that most self-adjusting dynamical systems that initially have chaotic behavior will also adapt toward the edge of chaos. A model for self-adjusting dynamical systems is introduced which treats the control parameters as slowly varying, rather than constant. The dynamics of these parameters is assumed to be governed by some low-pass filtered feedback from the dynamical variables of the system. Under the influence of noise, at least in numerical models, the probability of chaotic breakout shows a universal scaling with the duration of the breakouts. Applications of the model to biochemical oscillators as the simplest possible adaptive system relevent to environmental dynamics will be investigated. A high degree of interdisciplinarity is required, as the research involves expertise in dynamical systems, plant biology, instrumental measurements, cybernetics, enzymology, chemistry, and physics. The system is chosen to be "biocomplex," yet simple enough that meaningful measurements can be made and quantitative models can be evaluated. We intend to experimentally demonstrate adaptation using the peroxidase-oxidase oscillator as an example. This system is known to exhibit non-linear, complex, and even chaotic behavior. We will explore if the in situ behavior of this enzyme provides the first experimental evidence for adaptation to the edge of chaos in a naturally occurring system. Detailed chemical models are available to guide our experiments. We will experimentally implement low-pass filtered feedback from the dynamical variables to the control parameters through: 1. a computer based probe-actuator system, and 2. the comparatively slow response of the metabolism of a thin section of horseradish root tissues suspended in a reactor, and check for adaptation to the edge of chaos, and critical scaling of chaotic outbreaks of chemical oscillations. Outreach activities to local secondary schools will be incorporated into our existing collaborations with high school science teachers. If our initial experiments on plant peroxidases show the anticipated complexity, we will then explore the related complexity in the behavior of peroxidases and oxidases in human neutrophils, cells associated with anti-bacterial activity and response to systemic afronts.