Two species may be fully reproductively isolated at the point they meet, but be connected by continuous gene flow by a longer route around the back of a geographical barrier; such a ring species complex exists for the greenish warbler, and genomics shows that there have been several historical breaks in gene flow along the continuum, as well as some introgression between the end forms.
- Miguel Alcaide
- Elizabeth S. C. Scordato
- Darren E. Irwin
