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The Utah sucker (Catostomus ardens) is endemic to the Bonneville Basin and the upper Snake River drainage in western North America, and is thought to hybridize with the federally endangered June sucker (Chasmistes liorus mictus) in Utah Lake (Bonneville Basin). Here we describe the discovery of a major subdivision in Utah suckers (4.5% mitochondrial sequence divergence) between the ancient Snake River drainage and the Bonneville Basin. This boundary has not previously been recognized in Utah suckers based on morphologic variation, but has been recently described in two endemic cyprinids in the region. Populations in valleys east of the Wasatch Mountains in Utah clustered with the Snake River populations, suggesting...
The current distribution and status of populations of the southwestern toad, Bufo microscaphus, are of considerable interest given the suspected decline in anuran amphibians in the western United States (Blaustein and Wake 1990, Sweet 1991). This bufonid, typically associated with riparian habitats in the desert Southwest, is largely absent from much of its former range in southern California (Sweet personal communication). In Arizona and Utah, B. microscaphus is known to hybridize with a closely related toad, B. woodhousii, and it appears that B. woodhousii has replaced B. microscaphus at a number of localities (Sullivan 1986). Given the interest in this species and the lack of information on populations in Arizona,...
I analyzed temporal variation in hybridization between the southwestern toad (Bufo microscaphus) and Woodhouse's toad (Bufo woodhousii) along the Virgin River in southwestern Utah and northwestern Arizona. Bufo woodhousii is largely restricted to the floodplain of the Virgin River from southern Nevada to the vicinity of St. George, Utah. By contrast, B. microscaphus is confined primarily to the tributaries of the Virgin River, only occupying the Virgin River proper exclusive of B. woodhousii along its upper reaches east of La Verkin Creek. As in all other zones of sympatry for these bufonids, behavior and morphology provide clear evidence of hybridization at a number of sites along the Virgin River. Analysis of...
Hybridization between the southwestern toad (Bufo microscaphus) and Woodhouse's toad (B. woodhousii) along the Agua Fria and Hassayampa rivers in central Arizona was investigated over a 3-yr period. Variation in allozymes and the pulse rate of male release calls was compared with morphological variation in these taxa and their hybrids. At two sites on the Agua Fria drainage, data on release calls, but not morphology, were concordant with allozyme evidence of hybridization. At a third site on the Agua Fria, morphological data, but not release calls, corroborated electrophoretic evidence of hybridization. Along the Hassayampa River, all lines of evidence indicated that there has not yet been any hybridization in an...