Digest: Habitat associations shape a hybrid zone in killifish.

Hybrid zones provide valuable opportunities to interrogate the processes that drive speciation. In a new study, Hardy et al. (2025) demonstrate that the dominant vegetation type in patchy cordgrass salt marshes and mangrove swamps drives a mosaic hybrid zone between two species of killifish. Furthermore, the authors showed that hybridization is asymmetrical, and that Fundulus grandis is more likely to hybridize than F. heteroclitus. This study highlights the need for interdisciplinary study of the environmental context of reproductive isolation.