No evidence for assortative mating within a willow warbler migratory divide
Introduction: In contact zones, genetic mixing of two taxa can be restricted by prezygotic (e.g. assortative mating) or postzygotic (lower fitness of hybrid offspring) barriers, or a combination of the two. A hybrid zone between two willow warbler subspecies (Phylloscopus trochilus trochilus, P. t. acredula) with distinctive migratory strategies occurs in central Sweden. These subspecies exhibit d
