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DY: Fachverband Dynamik und Statistische Physik
DY 32: Statistical Physics in Biological Systems III (organised by BP)
DY 32.9: Talk
Thursday, March 17, 2011, 12:45–13:00, ZEU 260
The role of population size in the evolution of microbial populations — •Joachim Krug1, Kavita Jain2, and Su-Chan Park3 — 1Institut für Theoretische Physik, Universität zu Köln, Cologne, Germany — 2Theoretical Sciences Unit and Evolutionary and Organismal Biology Unit, Jawaharlal Nehru Centre, Bangalore, India — 3Department of Physics, The Catholic University of Korea, Bucheon, Korea
The speed of adaptation of a population placed into a new environment is generally expected to increase with increasing population size, for at least two reasons: The supply of beneficial mutations is proportional to population size, and the probability of fixation of deleterious mutations is negligible in large populations. Contrary to this expectation, recent experiments on microbial populations have shown that small populations evolving in a complex nutrient medium may achieve a higher fitness than large ones due to the increased heterogeneity of adaptive trajectories. We introduce a class of haploid three-locus fitness landscapes that allows to investigate this scenario in a precise and quantitative way. Our main result derived analytically shows how the probability of choosing the path of largest initial fitness increase grows with the population size. This makes large populations more likely to get trapped at local fitness peaks and implies an advantage of small populations at intermediate time scales. Additional studies using ensembles of random fitness landscapes show that the results achieved for a particular choice of three-locus landscape parameters are robust and also persist as the number of loci increases.