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Clonal Interference, Multiple Mutations, and Adaptation in Large Asexual Populations
Two important problems affect the ability of asexual populations to
accumulate beneficial mutations, and hence to adapt. First, clonal interference
causes some beneficial mutations to be outcompeted by more-fit mutations which
occur in the same genetic background. Second, multiple mutations occur in some
individuals, so even mutations of large effect can be outcompeted unless they
occur in a good genetic background which contains other beneficial mutations.
In this paper, we use a Monte Carlo simulation to study how these two factors
influence the adaptation of asexual populations. We find that the results
depend qualitatively on the shape of the distribution of the effects of
possible beneficial mutations. When this distribution falls off slower than
exponentially, clonal interference alone reasonably describes which mutations
dominate the adaptation, although it gives a misleading picture of the
evolutionary dynamics. When the distribution falls off faster than
exponentially, an analysis based on multiple mutations is more appropriate.
Using our simulations, we are able to explore the limits of validity of both of
these approaches, and we explore the complex dynamics in the regimes where
neither are fully applicable.Comment: 24 pages, 5 figure
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