Asymmetrical hybridization and environmental factors influence the spatial genetic structure of a killifish hybrid zone.

This article focuses on the spatial genetic structure and environmental influences shaping the hybrid zone between two sister killifish species, Fundulus heteroclitus and Fundulus grandis, in northeastern Florida. The study found that the hybrid zone spans approximately 37 km and exhibits a mosaic pattern of hybridization strongly associated with differences in dominant marsh vegetation—cordgrass for F. heteroclitus and mangroves for F. grandis—alongside other environmental factors such as salinity, temperature, and dissolved oxygen. Reproductive barriers were asymmetrical, with F. heteroclitus showing stronger conspecific mate preference and less hybridization where it is more abundant, while hybridization and introgression were more common where F. grandis predominates. These patterns suggest that environmental heterogeneity and species-specific reproductive behaviors influence the hybrid zone's structure and may affect how these species respond to ongoing climate-driven habitat changes, potentially leading to range shifts rather than adaptive introgression.