The rate and effects of spontaneous mutation on fitness traits in the social amoeba, Dictyostelium discoideum

We performed a mutation accumulation (MA) experiment using the social amoeba Dictyostelium discoideum to estimate the rate and distribution of effects of spontaneous mutations affecting eight putative fitness traits. We found that the per generation mutation rate for most fitness components is 0.0019 mutations per haploid genome per generation, or larger. This rate is an order of magnitude higher than estimates for fitness components in the unicellular eukaryote Saccharomyces cerevisiae, even though the base-pair substitution rate is two orders of magnitude lower. The high rate of fitness-altering mutations observed in this species may be partially explained by a large mutational target relative to Saccharomyces cerevisiae. Also, fitness-altering mutations may occur primarily at simple sequence repeats, which are common throughout the genome, including in coding regions, and may represent a target that is particularly likely to give fitness effects upon mutation. The majority of mutatio...