Semi-permeable species boundaries in the coral genus Madracis: Introgression in a brooding coral system

► The prevalence of hybridization among brooding coral species was so far unclear. ► Madracis taxa show recurrent non-monophyly and shared polymorphism. ► Simulations rejected lineage sorting alone as an explanation to the genetic variation. ► Introgressive hybridization plays an important role in the evolution of the genus. ► Disruptive selection keeps Madracis morphospecies recognizable.