Can changes in ploidy drive the evolution to allogamy in a selfing species complex?

Abstract

SummaryThe evolution of mating systems in plants is central for understanding the rise of their diversity on Earth. The transition towards self-fertilization is a well-known example of convergent evolution although the opposite direction is expected to be forbidden according to evolutionary theories. We suggest that the ploidy level could promote changes in the reproductive strategies through its effect on traits related to pollination.We performed controlled crosses on several populations from the polyploidErysimum incanumspecies complex, described as predominantly selfing, to evaluate the inbreeding depression. Additionally, we measured mating traits such as floral size, herkogamy, anther exertion, the relative investment in male and female components (P:O ratio) and genetic diversity.We described three ploidy levels in the complex – hexaploids were unknown until now. We found significant differences in the self-pollination success among ploidies and even among populations within the same ploidy. Inbreeding depression was present in higher ploidies, accompanied by bigger flowers with higher anther exposure, increased herkogamy and P:O and genetic diversity.These findings suggest that ploidy could be promoting alternative reproductive strategies to selfing, driving mating system diversification within a selfing species, which has not been previously described in the wild.