Population Evolution Dynamics Research Articles

Dynamics of bacterial adaptation.

Determining pattern in the dynamics of population evolution is a long-standing focus of evolutionary biology. Complementing the study of natural populations, microbial laboratory evolution experiments have become an important tool for addressing these dynamics because they allow detailed and replicated analysis of evolution in response to controlled environmental and genetic conditions. Key findings include a tendency for smoothly declining rates of adaptation during selection in constant environments, at least in part a reflection of antagonism between accumulating beneficial mutations, and a large number of beneficial mutations available to replicate populations leading to significant, but relatively low genetic parallelism, even as phenotypic characteristics show high similarity. Together, there is a picture of adaptation as a process with a varied and largely unpredictable genetic basis leading to much more similar phenotypic outcomes. Increasing sophistication of sequencing and genetic tools will allow insight into mechanisms behind these and other patterns.

Bifurcation Analysis in Population Genetics Model with Partial Selfing

A new model which allows both the effect of partial selfing selection and an exponential function of the expected payoff is considered. This combines ideas from genetics and evolutionary game theory. The aim of this work is to study the effects of partial selfing selection on the discrete dynamics of population evolution. It is shown that the system undergoes period doubling bifurcation, saddle-node bifurcation, and Neimark-Sacker bifurcation by using center manifold theorem and bifurcation theory. Numerical simulations are presented not only to illustrate our results with the theoretical analysis, but also to exhibit the complex dynamical behaviors, such as the period-3, 6 orbits, cascade of period-doubling bifurcation in period-2, 4, 8, and the chaotic sets. These results reveal richer dynamics of the discrete model compared with the model in Tao et al., 1999. The analysis and results in this paper are interesting in mathematics and biology.

Topological rearrangements during 2D normal grain growth

Topological rearrangements during grain growth in polycrystals provide an example of the strongest possible non-linearity in the grain population evolution dynamics. For a 2D grain the equation of growth is linear (von Neumann-Mullins law) until there is a topological change. The inevitable occurence of a topological rearrangement makes the system intrinsically non-linear, and the non-linearity effects are critical to understanding grain growth dynamics. In situ experimental investigation of topological rearrangements in thin polycrystalline films of succinonitrile (SCN) show that according to theoretical considerations (and contrary to conventional wisdom) small 4- and 5-sided quasi-2D grains usually shrink almost to the vanishing limit, without losing sides through the expected topological cascade of neighbor switchings. Vanishing grains generally do not create multiple vertices in the system. They do not shrink to a point as 2D soap froth bubbles do, but rather shrink to a line, with 2 vertices (in the case of 4-sided grains) or to two lines with 3 vertices (in the case of 5-sided grains). The experimental results are compared with those of direct computer simulation of 2D grain shrinking. The simulation shows also that the main topological results remain valid both in systems with uniform and anisotropic boundaries.