Evidence of convergent character displacement in release vocalizations of Bufo fowleri and Bufo terrestris (Anura; Bufonidae)

Anuran release vocalizations prevent prolonged amplexus of males by conspecific and heterospecific males, whereas advertisement vocalizations potentially act as a premating isolation mechanism. Selection favouring prompt release during heterospecific amplexus should result in convergent character displacement in release vocalizations. Conversely, selection should produce divergent character displacement in advertisement vocalizations. I examined call properties important to mate recognition from release and advertisement vocalizations of allopatric and sympatric populations of Bufo fowleri and B. terrestris to determine whether the two calls exhibit opposing patterns of character displacement. Results indicated convergent character displacement in the periodicity of release vocalizations (a measure equal to the inverse of pulse rate and an estimate of release vibration rate). The periodicity of advertisement vocalizations was significantly displaced from the allopatric character state resulting in greater divergence in sympatry. However, this parameter was already largely divergent in allopatry and, therefore, results were not consistent with the pattern expected for divergent character displacement. The dominant frequency of sympatric advertisement vocalizations was not significantly displaced from allopatry. Results for advertisement vocalizations provided evidence that convergence of release vocalizations was not the result of hybridization. There was no evidence that clinal variation accounted for displacement of call characteristics. Convergent character displacement in the periodicity of release vocalizations may facilitate interspecific communication during heterospecific amplexus, whereas divergent advertisement vocalizations promote species isolation.