Natural hybridization among distantly related toads (Bufo alvarius, Bufo cognatus, Bufo woodhousii) in central Arizona

Putative hybrid toads of the genus Bufo were collected in central Arizona and identified using allozymes, qualitative and quantitative morphological characters, and release call characteristics. Data suggest one hybrid resulted from mating between Bufo cognatus and Bufo woodhousii, and the other three resulted from matings between Bufo alvarius and B. woodhousii. Natural hybridization between these taxa has not been previously reported. To date, B. woodhousii has been found to hybridize with four species of the Bufo americanus species group, of which B. woodhousii is a member, and five other species which represent three outgroups to the B. americanus group. Fossil evidence suggests some genomic compatability has been retained between B. alvarius and B. woodhousii despite at least 6 million years of independent evolution. Hybridization among members of Bufo may be due to alternative mating tactics of males, such as active searching, and by alteration of historical habitats in central Arizona.