Anaxyrus williamsi
(Gordon, Simandle, and Tracy, 2017)
Dixie Valley Toad
G1Critically ImperiledGlobal Rank
Critically endangeredIUCN
Very highThreat Impact
U.S. Fish & Wildlife Service, https://www.usa.gov/government-works
Identity
Unique IDELEMENT_GLOBAL.2.106026
Element CodeAAABB01X10
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryVertebrate Animal
IUCNCritically endangered
Endemicendemic to a single state or province
KingdomAnimalia
PhylumCraniata
ClassAmphibia
OrderAnura
FamilyBufonidae
GenusAnaxyrus
Synonyms
Bufo williamsiGordon, Simandle, and Tracy, 2017
Concept Reference
Gordon, R., E. T. Simandle, and C. R. Tracy. 2017. A diamond in the rough desert shrublands of the Great Basin in the Western United States: A new cryptic toad species (Amphibia: Bufonidae: Bufo (Anaxyrus)) discovered in Northern Nevada. Zootaxa 4290:123–139.
Taxonomic Comments
The genus Anaxyrus was split from Bufo by Frost et al. (2006). However, taxonomy within the genus Bufo remains controversial and many references still use the long-established Bufo. Gordon et al. (2017) using 14 distinct morphological characteristics as well as genomic DNA extracted from tissue described the Dixie Valley toad as a distinct species: Anaxyrus williamsi.
Phylogenetic analysis of mtDNA data from throughout the range of the Bufo (Anaxyrus) boreas species group (including boreas, canorus, exsul, and nelsoni) by Goebel et al. (2009) identified three major haplotype clades. The Northwest clade (NW) includes both subspecies of boreas (boreas and halophilus) and divergent minor clades in the middle Rocky Mountains, coastal, and central regions of the west, and Pacific Northwest. However, Forrest et al. (2017) found very little mtDNA sequence difference for the Dixie Valley Toad (DVT) or McCoy Ranch toads (a population 50 km north of Dixie Valley) analyzed with respect to the range of A. boreas sequences presented by Goebel et al (2009). In fact, 6 of the DVT samples (DM1, DM3, DM4, DM6, DS1, and DS2) that were analyzed are identical to A. boreas sequences from Beaverhead County, Montana. The maximum likelihood phylogenetic analysis of the combined CR and COI data provides no evidence to support the hypothesis that the DVT is a distinct species or subspecies. Instead, the DVT forms part of the well-supported North Western A. boreas clade identified in Goebel et al. Here we follow Gordon et al. (2017) and USFWS in recognizing this taxon as A. williamsi.
Phylogenetic analysis of mtDNA data from throughout the range of the Bufo (Anaxyrus) boreas species group (including boreas, canorus, exsul, and nelsoni) by Goebel et al. (2009) identified three major haplotype clades. The Northwest clade (NW) includes both subspecies of boreas (boreas and halophilus) and divergent minor clades in the middle Rocky Mountains, coastal, and central regions of the west, and Pacific Northwest. However, Forrest et al. (2017) found very little mtDNA sequence difference for the Dixie Valley Toad (DVT) or McCoy Ranch toads (a population 50 km north of Dixie Valley) analyzed with respect to the range of A. boreas sequences presented by Goebel et al (2009). In fact, 6 of the DVT samples (DM1, DM3, DM4, DM6, DS1, and DS2) that were analyzed are identical to A. boreas sequences from Beaverhead County, Montana. The maximum likelihood phylogenetic analysis of the combined CR and COI data provides no evidence to support the hypothesis that the DVT is a distinct species or subspecies. Instead, the DVT forms part of the well-supported North Western A. boreas clade identified in Goebel et al. Here we follow Gordon et al. (2017) and USFWS in recognizing this taxon as A. williamsi.
Conservation Status
Rank MethodLegacy Rank calculation - Biotics v1
Review Date2019-12-29
Change Date2019-10-16
Edition Date2019-12-29
Edition AuthorsMiskow, E. NDNH
Threat ImpactVery high
Range Extent<100-250 square km (less than about 40-100 square miles)
Number of Occurrences1 - 5
Rank Reasons
Restricted to one small thermal wetland area in Dixie Meadows, Nevada.
Range Extent Comments
Restricted to Dixie Hot Springs outside of direct thermal water in marsh area in the western portion of Dixie Valley.
Occurrences Comments
Toads occur in a single habitat patch of ~ 145 hectares. During the 2018 surveys, 142 adult observations of adult toads were made during two survey efforts totaling 10 days.
Threat Impact Comments
Development of geothermal energy and difficulty in associated mitigation, decrease in spring discharge, changes in water temperature, and groundwater extraction; and chytridiomycosis disease and predation by the invasive American bullfrog all impact the persistence of the toad.
Ecology & Habitat
Description
The Dixie Valley toad is distinctive among western toads, with chromatic hues of olive with small, diverse and irregular black flecks. Face heavily specked. Upper eyelids flecked black against olive background color. Pupil black, horizontal, with gold-streaked iris. Parotoid glands tan; minor black spotting on crown of gland with black streaks along margins. Rust colored tubercles irregularly distributed across dorsum, small but variable in size, with black margins. Tubercles between mid-axillary line and articulation with femur rust colored, bordered by fine black halos. Dorsal stripe cream, originating at interorbital space, broken just posterior to terminal margin of parotoid glands, resumes along vertebral region, and terminates at sacral hump. Forearms with black flecks dorsally and medium to dark brown overlying olive background. Hind legs with rusty tubercles arranged atop dark brown banding overlying ground olive color with black flecking. Inferior to midaxillary line, tubercles diminish in size until absent. Inferior mid-axillary line with heavy black mottling against white. Small black spots along inferior lower labial margin. Anterior forearms and hind legs heavily marbled black against the white background color. Throat white, immaculate. White venter heavily mottled in black; seat patch conspicuous and dark brown, with round, white spotting. Undersides of hands and feet dark gray. Tubercles of hands and feet, fingers, and toes bright orange (Gordon, 2017).
Diagnostic Characteristics
The Dixie Valley toad has the smallest body size in the Anaxyrus (Bufo) species complex, the snout-vent-length is more than 2.5 cm smaller than other western toads, and can be further diagnosed from other species in the complex by its shorter hind limbs, conspicuously large and elevated tibial glands and unique color pattern.
Habitat
Found in or near an isolated wetland and associated springs in Dixie Valley. Dixie Valley toads have not been observed within the warmer portions of the Dixie Hot Springs, however much of this habitat is overgrown by dense vegetation. Dixie Valley toads may also benefit from the constant temperatures available year-round in the thermal springs and nearby warm-water wells.
Terrestrial Habitats
Shrubland/chaparral
Other Nations (1)
United StatesNU
| Province | Rank | Native |
|---|---|---|
| Nevada | S1 | Yes |
Threat Assessments
| Threat | Scope | Severity | Timing |
|---|---|---|---|
| 3 - Energy production & mining | Large (31-70%) | Serious or 31-70% pop. decline | High (continuing) |
| 3.3 - Renewable energy | Large (31-70%) | Serious or 31-70% pop. decline | High (continuing) |
| 7 - Natural system modifications | Pervasive (71-100%) | Extreme or 71-100% pop. decline | High (continuing) |
| 7.2 - Dams & water management/use | Pervasive (71-100%) | Extreme or 71-100% pop. decline | High (continuing) |
| 7.2.1 - Abstraction of surface water (domestic use) | Pervasive (71-100%) | Extreme or 71-100% pop. decline | High (continuing) |
| 8 - Invasive & other problematic species, genes & diseases | Restricted - small | Moderate - slight | Unknown |
Roadless Areas (1)
South Dakota (1)
| Area | Forest | Acres |
|---|---|---|
| Indian Creek | Buffalo Gap National Grassland | 24,666 |
References (10)
- Forrest, M. J., J. Stiller, T.L. King, and G. W. Rouse. 2017. Between hot rocks and dry places: the status of the Dixie Valley Toad. Western North American Naturalist 77(2):162-175.
- Frost, D. R. 2010. Amphibian Species of the World: an Online Reference. Version 5.4 (8 April 2010). Electronic Database accessible at http://research.amnh.org/herpetology/amphibia/index.php. American Museum of Natural History, New York, USA.
- Frost, D.R. 2020. Amphibian Species of the World: an Online Reference. Version 6.0. American Museum of Natural History, New York, USA. Online: http://research.amnh.org/herpetology/amphibia/index.html
- Frost, D.R., T. Grant, J. Faivovich, R. Bain, A. Haas, C.F.B. Haddad, R.O. de Sa´, S.C. Donnellan, C.J. Raxworthy, M. Wilkinson, A. Channing, J.A. Campbell, B.L. Blotto, P. Moler, R.C. Drewes, R.A. Nussbaum, J.D. Lynch, D. Green, and W.C. Wheeler. 2006. The amphibian tree of life. Bulletin of the American Museum of Natural History 297: 1-370.
- Goebel, A. M., T. A. Ranker, P. S. Corn, and R. G. Olmstead. 2009. Mitochondrial DNA evolution in the <i>Anaxyrus boreas</i> species group. Molecular Phylogenetics and Evolution 50:209-225.
- Gordon, R., E. T. Simandle, and C. R. Tracy. 2017. A diamond in the rough desert shrublands of the Great Basin in the Western United States: A new cryptic toad species (Amphibia: Bufonidae: <i>Bufo </i>(<i>Anaxyrus</i>)) discovered in Northern Nevada. Zootaxa 4290:123–139.
- U.S. Fish and Wildlife Service (USFWS). 2018. Endangered and Threatened Wildlife and Plants; 90-day Findings for Three Species. Federal Register 83(124):30091-30094.
- U.S. Fish and Wildlife Service (USFWS). 2022. Endangered and Threatened Species: Status for the Dixie Valley Toad. Proposed rule. Federal Register 87(67):20374-20378.
- U.S. Fish and Wildlife Service (USFWS). 2022. Endangered and Threatened Wildlife and Plants; Emergency Listing of the Dixie Valley Toad as Endangered. Temporary rule; emergency action. Federal Register 87(67):20336-20348.
- U.S. Fish and Wildlife Service (USFWS). 2022. Endangered and Threatened Wildlife and Plants; Endangered Species Status for the Dixie Valley Toad. Final rule. Federal Register 87(231):73971-73994.