Phase transition behaviour in yeast and bacterial populations under stress

Nonlinear physics perspective and essential disease dynamics of EBV infections and the dynamics of EBV-associated diseases

The Epstein-Barr virus affects more than 90% of the world population and, consequently, is a virus whose infection dynamics should not be overlooked. It can cause the disease infectious mononucleosis and comes with other virus-associated diseases and conditions ranging from certain cancers to episodes of fatigue and depression. While previous epidemiological and virological modeling studies have worked out the details of possible infection dynamics scenarios, the current study takes a different approach. Using a nonlinear physics perspective and a fairly general epidemiological model, we identify the essential EBV infection dynamics along its so-called infection order parameter. We demonstrate that the essential dynamics describes the initial path that EBV infections take in the multi-dimensional model space. In particular, we show that the essential dynamics predicts the initial dynamics of the relevant subpopulations and describes how the subpopulations involved in an EBV infection outbreak organize themselves during the outbreak. Intervention and prevention measures are discussed in the context of the nonlinear physics perspective. An adverse synergy effect between two infection rate parameters is identified. An early warning system based on the so-called critical slowing down phenomenon is proposed for EBV infection waves in college and university student populations, which are populations particularly vulnerable to EBV infections.

Evolutionary shift of a tipping point can precipitate, or forestall, collapse in a microbial community

Global ecosystems are rapidly approaching tipping points, where minute shifts can lead to drastic ecological changes. Theory predicts that evolution can shape a system's tipping point behaviour, but direct experimental support is lacking. Here we investigate the power of evolutionary processes to alter these critical thresholds and protect an ecological community from collapse. To do this, we propagate a two-species microbial system composed of Escherichia coli and baker's yeast, Saccharomyces cerevisiae, for over 4,000 generations, and map ecological stability before and after coevolution. Our results reveal that tipping points-and other geometric properties of ecological communities-can evolve to alter the range of conditions under which our microbial community can flourish. We develop a mathematical model to illustrate how evolutionary changes in parameters such as growth rate, carrying capacity and resistance to environmental change affect ecological resilience. Our study shows that adaptation of key species can shift an ecological community's tipping point, potentially promoting ecological stability or accelerating collapse.

Phase transitions in evolutionary dynamics

Sharp changes in state, such as transitions from survival to extinction, are hallmarks of evolutionary dynamics in biological systems. These transitions can be explored using the techniques of statistical physics and the physics of nonlinear and complex systems. For example, a survival-to-extinction transition can be characterized as a non-equilibrium phase transition to an absorbing state. Here, we review the literature on phase transitions in evolutionary dynamics. We discuss directed percolation transitions in cellular automata and evolutionary models, and models that diverge from the directed percolation universality class. We explore in detail an example of an absorbing phase transition in an agent-based model of evolutionary dynamics, including previously unpublished data demonstrating similarity to, but also divergence from, directed percolation, as well as evidence for phase transition behavior at multiple levels of the model system's evolutionary structure. We discuss phase transition models of the error catastrophe in RNA virus dynamics and phase transition models for transition from chemistry to biochemistry, i.e., the origin of life. We conclude with a review of phase transition dynamics in models of natural selection, discuss the possible role of phase transitions in unraveling fundamental unresolved questions regarding multilevel selection and the major evolutionary transitions, and assess the future outlook for phase transitions in the investigation of evolutionary dynamics.

Phase transitions in biology: from bird flocks to population dynamics

Phase transitions are an important and extensively studied concept in physics. The insights derived from understanding phase transitions in physics have recently and successfully been applied to a number of different phenomena in biological systems. Here, we provide a brief review of phase transitions and their role in explaining biological processes ranging from collective behaviour in animal flocks to neuronal firing. We also highlight a new and exciting area where phase transition theory is particularly applicable: population collapse and extinction. We discuss how phase transition theory can give insight into a range of extinction events such as population decline due to climate change or microbial responses to stressors such as antibiotic treatment.