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 experime ntal systems. In light of this. growing trend, we propose a simple populati on genetic model for the evolution of gametophytic self-incompatibility, in corporating 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 incompatib ility conferred by the allele. We confirm earlier results that inbreeding d epression 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 s elf-incompatibility to become established. Finally, we show that the domina nce of the mutant allele has-a greater impact on the fate of a newly arisen self-incompatibility allele than the strength of the incompatibility confe rred by the allele. In particular, the more recessive the self-incompatibil ity expression in heterozygote stigmas and the weaker the response induced, the easier it is for a self-incompatibility allele to invade.