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BP: Fachverband Biologische Physik

BP 21: Population Dynamics and Evolution

BP 21.1: Talk

Thursday, February 28, 2008, 12:15–12:30, C 243

Clonal interference in large populations — •Su-Chan Park and Joachim Krug — Institut für Theoretische Physik, Universität zu Köln, Köln, Germany

Clonal interference, the competition between lineages arising from different beneficial mutations in an asexually reproducing population, is an important factor determining the tempo and mode of microbial adaptation. The standard theory of this phenomenon neglects the occurrence of multiple mutations as well as the correlation between loss by genetic drift and clonal competition, which is questionable in large populations. Working within the Wright-Fisher model with multiplicative fitness (no epistasis), we determine the rate of adaptation asymptotically for very large population sizes and show that the standard theory fails in this regime. Our study also explains the success of the standard theory in predicting the rate of adaptation for moderately large populations. Furthermore we show that the nature of the substitution process changes qualitatively when multiple mutations are allowed for, since several mutations can be fixed in a single fixation event. As a consequence, the index of dispersion for counts of the fixation process displays a minimum as a function of population size, while the origination process of fixed mutations becomes completely regular for very large populations. We find that the number of mutations fixed in a single event is geometrically distributed as in the neutral case.

Reference: S.-C. Park and J. Krug, PNAS 104, 18135 (2007).