Pollen transfer dynamics and the evolution of gametophytic self-incompatibility

Recent studies of mating system evolution have attempted to include aspects of pollination biology in analysis of both theoretical models and experimental systems. In light of this growing trend, we propose a simple population genetic model for the evolution of gametophytic self-incompatibility, incorporating parameters for pollen discounting and pollen export/capture. In this model, we consider several cases that span the spectrum for dominance of the mutant self-incompatibility allele and for the degree of incompatibility conferred by the allele. We confirm earlier results that inbreeding depression is required for successful invasion of the self-incompatibility allele and we demonstrate that, unless pollen discounting is very low, the level of inbreeding depression must be very high for an allele conferring self-incompatibility to become established. Finally, we show that the dominance of the mutant allele has a greater impact on the fate of a newly arisen self-incompatibility allele than the strength of the incompatibility conferred by the allele. In particular, the more recessive the self-incompatibility expression in heterozygote stigmas and the weaker the response induced, the easier it is for a self-incompatibility allele to invade.     

S-RNase-mediated gametophytic self-incompatibility is ancestral in eudicots

The evolutionary relationship between self-incompatibility systems in different families of flowering plants has long been a topic of interest. Physiological differences in the mode of gene action and the enormous sequence differences between genes with different modes of action suggest that many instances of self-incompatibility have arisen independently. In contrast, previous analyses of the S-RNase associated with gametophytic self-incompatibility in the eudicot families (Solanaceae, Scrophulariaceae, and Rosaceae) have suggested that sequences within families form well-supported and distinct lineages. In this study we demonstrate that in fact, S-RNase-mediated gametophytic self-incompatibility evolved only once in the eudicots.