Contemporary Evolution of Reproductive Isolation and Phenotypic Divergence in Sympatry along a Migratory Divide

SummaryUnderstanding the influence of human-induced changes on the evolutionary trajectories of populations is a fundamental problem [1, 2]. The evolution of reproductive isolation in sympatry is rare, relying on strong selection along steep ecological gradients [3–7]. Improved wintering conditions owing to human activities promoted the recent establishment of a migratory divide in Central European blackcaps (Sylvia atricapilla) [8, 9]. Here, we show that differential migratory orientation facilitated reproductive isolation of sympatric populations within