Postmating reproductive isolation in pseudophryne and the evolutionary significance of hybrid zones.

Hybrid zones involving Pseudophryne (Anura: Leptodactylidae) provide direct evidence for the operation of postmating reproductive isolating mechanisms in animals in a natural situation. Significant introgression is prevented by hybrid inviability but there is no evidence for the reinforcement of premating isolating mechanisms. These parapatric hybrid zones are of unknown etiology, but are interpreted as being relatively old and persistent.