Preferring the fittest mates: An analytically tractable model

► We present a population-genetic model of a preference for fit mating partners. ► The alleles coding the mating preference go rapidly to fixation. ► The selection differentials between different niches are potentiated. ► The polymorphism exceeds the selection-migration equilibrium by several magnitudes. ► Fitness-based mating can be seen as a trigger of prezygotic isolation and divergence.