Genetic and environmental causes and evolutionary consequences of variations in self-fertility in self incompatible species

Within many self incompatible species there is variation among plants in self-fertility. Mutations conferring partial or complete self-fertility occur in the Salleles themselves, in genes closely linked to the S-alleles or in unlinked genes that affect the downstream rejection pathway, in unlinked genes that modify the expression or turnover of the S-allele products, and in unlinked genes that modify the pistil environment. Populations with genetic polymorphisms for self-fertility can be used as natural laboratories to examine the dynamic interplay of the forces that shape the evolution of plant breeding systems.We find that all self-fertility mutations are beneficial in populations with few S-alleles and/or high rates of pollen limitation and they may result in stable polymorphisms when there are high levels of inbreeding depression and/or S-linked load as might occur in highly fragmented or low density populations and in those species prone to repeated bouts of colonisation and extinction.