The process of ecotype formation has been invoked as an important driver of postglacial biodiversity, because many species colonized heterogeneous habitats and subsequently experienced divergent selection. Ecotype formation has been predominantly studied in outcrossing taxa, while far less attention has been paid to the implications of mating system shifts. Here we studied the genomic footprint of ecotype formation in Arabidopsis lyrata subsp. lyrata. The species colonized both rocky and sandy substrates during its postglacial range...