Secondary contact between incipient species provides the opportunity to understand how trait divergence restricts gene flow. While mating system transitions are particularly common and involve a suite of phenotypic changes, the extent to which these changes influence gene flow during speciation is poorly understood. Using 410 genomes, we quantified introgression between selfing-outcrossing sister Clarkia taxa in four independent contact zones. We used common garden and geospatial data to determi