Character Displacement in Frogs

Additional evidence has accumulated over the past 20 years regardingthe significance of the anuran mating call and regarding reinforcementof this premating isolating mechanism when hybridization occursin zones of symnatry. No two sympatric species have the samecall. That the mating call is a home-specific mate attractanthas been demonstrated in five major anuran families. Discriminationagainst hybrid calls versus homospecific calls has been demonstratedin Bufo and Hyla. Principal examples of presumed reinforcementcontinue to be in Gastrophryne, Acris, and the Australian Hylaewingi group. Reinforcement may be the basis for striking differentiationof some populations of Scaphiopus bombifrons. Sympatric speciespairs of anurans show greater differentiation in call than doallopatric pairs in the same group. One hybridizing situationin Bufo appears to have changed over 30 years to discrete populationswithout intermediate calls. Effective call differences can evolvewithout sympatry, and there are sympatric situations in whichno reinforcement is evident.