Parent-offspring and sexual conflicts in the evolution of angiosperm seeds

In angiosperm plants the parental investment consists mainly of the endospe rm, a nutritive tissue formed by genetic elements from both parents and use d upon germination. We analyze a one-locus model of the evolution of the en dosperm assuming that the alleles expressed in the endosperm determine the seed provisioning. In the model, we assume that large endosperm increases t he probability of survival when young, but decreases seed set when the plan t has reached the reproductive stage. We show that there is an evolutionari ly stable strategy (ESS) of endosperm amount which is influenced by mating system, ploidy of the endosperm, paternity and genomically imprinted genes with parent-specific expression. The ESS value is higher than the Value whi ch maximizes the reproductive success of the plant. When the maternal genet ic contribution is higher than the paternal (e.g. Polygonum plants), the ES S is almost always lower than when the parents have equal influence over th e endosperm as in Oenothera plants. In both types, increasing the number of pollen donors to a seed crop selects for higher levels of endosperm. Accor dingly, genes expressed only when inherited from the father are selected fo r higher endosperm amounts than genes expressed only when inherited from th e mother, except when all seed have the same pollen parent. ESS values for imprinted genes do not differ between Polygonum and Oenothera types of plan ts. The ESS Values are shown to be both locally and globally stable. The re sults are discussed in relation to evolutionary conflicts between the sexes .