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 a nd identified using allozymes, qualitative and quantitative morphological c haracters, and release call characteristics. Data suggest one hybrid result ed from mating between Bufo cognatus and Bufo woodhousii, and the other thr ee resulted from matings between Bufo alvarius and B. woodhousii. Natural h ybridization between these taxa has not been previously reported. To date, B. woodhousii has been found to hybridize with four species of the Bufo ame ricanus species group, of which B. woodhousii is a member, and five other s pecies which represent three outgroups to the B. americanus group. Fossil e vidence suggests some genomic compatibility has been retained between B. al varius and B. woodhousii despite at least 6 million years of independent ev olution. Hybridization among members of Bufo may be due to alternative mati ng tactics of males, such as active searching, and by alteration of histori cal habitats in central Arizona.