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DY: Fachverband Dynamik und Statistische Physik

DY 36: Statistical Physics in Biological Systems IV (organised by BP)

DY 36.7: Talk

Thursday, March 17, 2011, 15:45–16:00, ZEU 260

Stochastic slowdown in evolutionary processes — •Philipp M. Altrock, Chaitanya S. Gokhale, and Arne Traulsen — Max-Planck-Institute for Evolutionary Biology, Plön

We examine birth--death processes with state dependent transition probabilities and at least one absorbing boundary. In evolution, this describes selection acting on two different types in a finite population where reproductive events occur successively. If the two types have equal fitness the system performs a random walk. If one type has a fitness advantage it is favored by selection, which introduces a bias (asymmetry) in the transition probabilities. How long does it take until advantageous mutants have invaded and taken over? Surprisingly, we find that the average time of such a process can increase, even if the mutant type always has a fitness advantage. We discuss this finding for the Moran process and develop a simplified model which allows a more intuitive understanding. We show that this effect can occur for weak but non--vanishing bias (selection) in the state dependent transition rates and infer the scaling with system size. We also address the Wright--Fisher model commonly used in population genetics, which shows that this stochastic slowdown is not restricted to birth--death processes.

[1] Altrock, Gokhale, and Traulsen, Physical Review E 82, 011925 (2010)