Character Displacement in Frogs

Additional evidence has accumulated over the past 20 years regarding the significance of the anuran mating call and regarding reinforcement of this premating isolating mechanism when hybridization occurs in zones of symnatry. No two sympatric species have the same call. That the mating call is a home-specific mate attractant has been demonstrated in five major anuran families. Discrimination against hybrid calls versus homospecific calls has been demonstrated in Bufo and Hyla . Principal examples of presumed reinforcement continue to be in Gastrophryne , Acris , and the Australian Hyla ewingi group. Reinforcement may be the basis for striking differentiation of some populations of Scaphiopus bombifrons . Sympatric species pairs of anurans show greater differentiation in call than do allopatric pairs in the same group. One hybridizing situation in Bufo appears to have changed over 30 years to discrete populations without intermediate calls. Effective call differences can evolve without sympatry, and there are sympatric situations in which no reinforcement is evident.