On November 27, 2007, PED Seminar Series Presents

Clonal interference in large populations

by Prof. Joachim Krug

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 theory of this phenomenon developed by Gerrish and Lenski (GL) neglects the occurrence of multiple mutations, which is questionable in large populations. Here we examine the breakdown of the GL theory at large population sizes, using a combination of simulations and analytic considerations (1). We find that the rate of adaptation is surprisingly well described by GL theory, but the statistical nature of the substitution process changes qualitatively when multiple mutations are allowed for, since several mutations can be fixed in a single event. As a consequence, the index of dispersion of the fixation process displays a minimum as a function of population size, while the origination process of fixed mutations becomes completely regular. The number of mutations fixed in a single event is geometrically distributed.

1. Park SC, J Krug (2007). P Natl Acad Sci USA 104: 18135-18140.

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