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.Comment: 35 pages, 8 figures, 4 table