Evolutionary Innovation by Polyploidy

The preferred conditions for evolutionary innovation represent a fundamental question, but little is known experimentally or theoretically. In this study, we focused on the potential role of polyploidy in the evolution of novel traits. We proposed a simple model and demonstrated that the evolutionary rate of polyploids is similar to more much slower than that of haploids under neutral selection or during gradual evolution. However, experiments using polyploid cyanobacteria demonstrated that the probability of achieving antibiotic resistance increased with the number of chromosomes and implied an optimal number of chromosomes. Then, we investigated the dynamics of the same model on a fitness landscape in which cells should jump over a lethal valley to increase their fitness. The evolutionary rate could be increased in polyploidy, and the optimal number of chromosomes was identified. Further, we proposed that the optimization for evolutionary innovation might determine the number of chromosomes in polyploid bacteria.