Coenonympha tullia on Islands in the St. Lawrence River

The philosophy of subspeciation among animals requires that these taxa be essentially reproductively isolated. When such isolation does not exist clines appear. We believe that we have discovered one of the rare occasions when two well-defined subspecies, considered by some taxonomists to be two species, occupy the same terrain and where some degree of hybridization has taken place with the production of a hybrid brood that is temporally isolated from one subspecies and geographically from the other. Neither isolation may be absolute but that condition is closely approached.