The creation-mutation-selection model: mutation rates and effective population sizes

Abstract

AbstractThe creation-selection-mutation model makes predictions regarding the fitness of asexual and sexual populations in an environment that incorporates both positive and negative selection. The model predicts the optimal spontaneous mutation rate for a sexual population as one in which the fitness losses associated with positive and negative selection are equal. The model depends upon three mutation related rates: the rate of adaptive mutational opportunities, the rate of negative mutational site creation, and the spontaneous mutation rate. These three mutation related rates are estimated based on a comparison of substitution rates at nonsynonymous and synonymous sites in the genomes of related eukaryotic species. For eukaryotes, the rate of adaptive mutation opportunities is found to typically be in the range 10−3to 10−2population wide adaptive mutational opportunity sites per sexual generation. Negative sites are typically created at the rate 10−1to 101sites per haploid genome per sexual generation. And the spontaneous mutation rate is typically in the range 10−9to 10−8spontaneous mutations per creation-mutation-selection model site per sexual generation. Effective population sizes are also computed based on the assumption of optimal mutation rates. That effective population sizes appear reasonable, adds some evidence to the claim that evolution tunes the mutation rate towards a near optimal value.