Helminths of the southwestern toad, Bufo microscaphus, Woodhouse's toad, Bufo woodhousii (Bufonidae), and their hybrids from central Arizona

Great Basin Naturalist 56(4). © 1996. pp. 369-374 HELMINTHS OF THE SOUTHWESTERN TOAD, BUFO MICROSCAPHUS, WOODHOUSE'S TOAD, BUFO WOODHOUSII (BUFONIDAE), AND THEIR HYBRIDS FROM CENTRAL ARIZONA Stephen R. CoUlluM-ui. Cliarles H. Bursey-, Keith 13. Malmo.s'^ Brian K. Snllivan"\ and Ha\ Cheain' AB-STRACT. — The gastrointestinal tracts, lungs, and iirinar\' hladders from 77 Btifo inicroscaijIiiLs, 61 Bufo woodhousii, and (S of their hyhrids were e.xamined for helminths. One species of trematode {Glyptlwlinins quiela), 1 species of ces-tode {Distoichotnetra bttfimis), and 5 species of nematodes {Aph'cianu incerta, A. itzocancims, Rhabdias americanus, Physaloptcra sp., and Physocephalus sp.) were found. The greatest prevalence (41%) and mean intensity (231.7) were recorded ihv Aplcctiina iiiccrta in Bufo icoodhoii.sii. !t appears h\hrids Iiarhoi-fewei-i:iarasites than either parent species. Key icords: Iwhniutlis. Bulo microscaphus, Huto woodhousii, hyhrids. Arizniia. The southwestern toad {Bnjo uiicroscapluts Cope, 1866) is presently recognized as 3 allo-patric subspecies: B. )n. californicus Camp, 1915, which occurs in coastal southern California and northwest Baja California; B. m. microsca-phus Cope, 1866, found in southern Nevada and Utah, Arizona, and New Mexico; and B. m. mexicanus Brocchi, 1879, which occurs in the Sierra Madre Occidental of central Me.xico south to Durango (Price and Sullivan 1988). Woodhouse's toad {Bufo woodhousii Cirard, 1854) is recognized as 4 subspecies: B. w. wood-housii Cirard, 1854 occurs in eastern Montana and North Dakota, south through the plains states to central Texas and west of the Rocky Mountains from Idaho south to Colorado and Arizona with isolated populations in west Texas, southeastern California, and along the Oregon-Washington border; Bufo w. austrolis Shannon and Lowe, 1955 is found from central Colorado through New Mexico and Arizona to Sonora, Mexico, and iilong the Rio Crande drainage into southwest Texas and adjacent Mexico; Bufo w. velatus Bragg and Sanders, 1951 is restricted to northeast Texas; and B. w. fowled Hinckley, 1882 is widespread throughout much of the eastern United States south to the Culf Coast and west to eastern Te.xas (Beliler and King 1979). The toads examined during this study, B. in. microscaphus and B. w. austraUs, are known to li> bridize in Arizona (Sullivan 1986, Sullivan and Lamb 1988). Altliough diere are reports of helminths from B. microscaphus (Pany and Cnmdmann 1965) and B. woodhousii (Trowbridge and Heflev 1933, Brandt 1936, Walton 1938, Reiber et af. 1940, Kuntz 1941, Kuntz and Self 1944, Rankin 1945, Fantliam and Porter 1948, Frandsen and Crund-mann 1960, Pany and Crundmann 1965, Camp-bell 1968, Brooks 1976, Jilek and Wolff 1978, Baker 1985, Hardin and Janovy 1988, McAUister et al. 1989), populations of tliese toads from Ari-zona have not been examined. Concern over declining amphibian populations (Heyer et al. 1994) has increased interest in die possible nega-tive effects of parasites on toads. The puqDOse of tliis paper is to report on helminths of tliese toads and dieir hybrids from Aiizona. This investigation of parasitism in these toads addresses a hypothesis of hybrid zone theory and species boundaries. The hypothesis that populations of hybrid individuals with reduced fitness act as barriers to gene flow between 2 species separated by a hybrid zone (Biuton 1979, 1980) could have several mechanisms. One mechanism, increased parasitism of hybrids, is evaluated in this study. Two previous studies of parasitism in vertebrates are split. Hybrid mice {Mus muscuhis X Mus domesticus), specifically backcrossed hybrids, had greater numbers of cestode and nematode parasites than either parental species (Sage et al. 1986). Prevalence of monogenean parasites for hybrid minnows {Barhus barhus X Barhus meridiomiUs) was ^Department of Biology, Whittier College, Whittier, CA 90608. ^Department of Biology; Pennsylvania State University, Shenango Valley Campus, 147 Shenango Avenue, Sharon, PA 16146. ■^Department of Life Sciences, Bo.x .37100, Arizona State I'niversity West, Phoeni.x, .AZ 8.5069. 369

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Helminths of the southwestern toad, Bufo microscaphus, Woodhouse's toad, Bufo woodhousii (Bufonidae), and their hybrids from central Arizona

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