Studies that examine the genetic consequences of hybridization and introgression (gene exchange among species) have traditionally considered the genome a single entity. However, the concept of a porous genome suggests differential rates of introgression across the genome as a result of different selective pressures; loci under balancing selection are likely to show high rates of introgression, while loci under divergent selection will resist introgression. The action of these different selective pressures results in variation in both the level of genetic diversity and divergence across the genome. In this project I will focus on the effect of balancing selection at the self-incompatibility locus and compare this to neutral processes (genomic background) and flower colour genes subject to divergent selection. The Antirrhinum system provides a unique opportunity to test these ideas because it has both well-characterized self-incompatibility and flower colour variation. Interestingly, to date, research on hybridization and mating systems have remained largely separate fields, despite the potential importance of mating system for the outcomes of hybridization and patterns of genetic variation across the genome. In this proposal I aim to bring together these distinct fields to assess the role of self-incompatibility in the evolutionary dynamics of hybridization in Antirrhinum by comparing how genetic signatures of selection vary across the genome. To address these questions I will use a combination of molecular genetics, genomics, crossing experiments and ecological approaches. Together, these data will enable a comprehensive examination of the genetic consequences of selection and gene flow across the genome, and whether there is adaptive introgression among species.