Hybridization between the toads Bufo microscaphus and Bufo woodhousii in Arizona: variation in release calls and allozymes

Hybridization between the southwestern toad and Woodhouse's toad was investigated. Variation in allozymes and the pulse rate of male release calls was compared with morphological variation in these taxa and their hybrids. At 2 sites on the Agua Fria drainage, data on release calls, but not morphology, were concordant with allozyme evidence of hybridization. At a 3rd site on the Agua Fria, morphological data, but not release calls, corroborated electrophoretic evidence of hybridization. Along the Hassayampa River, evidence indicated that there has not yet been any hybridization in an area of recent sympatry. Temporal changes at one site along the Agua Fria River are consistent with the hypothesis that hybrid zones between these toads are unstable and that B. woodhousii is replacing B. microscaphus. -from Authors