The effects of ploidy and mating system on the evolvability of populations: theoretical and empirical investigations

Polyploidy has been associated in theoretical works with better adaptive potential, even though it is related to higher selfing rates. Self-fertilization causes an increase in homozygosity and has been related to weaker evolvability. However, there is a lack of empirical studies about the joint effects of polyploidy and selfing on genetic variance. We studied genetic variance in Erysimum incanum, a Brassicaceae selfing species from the Western Mediterranean basin with three different ploidy levels. We measured a series of phenotypic traits in individuals of each ploidy, obtained by controlled crosses and grown in different climatic conditions. For comparison, we also conducted mathematical simulations to explore how genetic diversity could be affected by the ploidy level and mating system. While theoretical approaches showed a positive relationship between ploidy and genetic variance and inbreeding depression, empirical results show lower evolvability and transgressive segregation for polyploids, related also to environmental conditions. Genetic variance in E. incanum polyploids could be related with recent establishment and adaptation to harsh environments, which explains the apparent contradiction with theory, where more settled and established populations are considered.