Bufo (Anaxyrus) nevadensis, Gordon & Simandle & Sandmeier & Tracy, 2020

Gordon, Michelle R., Simandle, Eric T., Sandmeier, Franziska C. & Tracy, C. Richard, 2020, Two New Cryptic Endemic Toads of Bufo Discovered in Central Nevada, Western United States (Amphibia: Bufonidae: Bufo [Anaxyrus]), Copeia 108 (1), pp. 166-183 : 2025-2030

Bufo (Anaxyrus) nevadensis , new species urn:lsid:zoobank.org:act:D9F8FACC-74DB-4D01-84AE-07CCB9400188

Railroad Valley Toad

Figures 1–4 , 5B , 6 ; Tables 1, 4–5

Holotype.— CAS 259272 , adult female ( Fig. 6 , Table 1), United States, Nevada, Nye County, Railroad Valley, Locke’s Preserve , 38833 0 9.1 00 N, 115846 0 12.8 00 W, M. R. Gordon , 5 May 2015.

Paratypes.— UNR 7905 , adult male ; UNR 7906 , adult female ; UNR 7907 , adult female ; UNR 7908 , adult male ; UNR 7909 , adult female; all individuals collected within the identified home range in Railroad Valley , 38833 0 9.1 00 N, 115846 0 12.8 00 W, M . R. Gordon, K. Guadalupe, and C. Burg , 5 May 2015 ( Fig. 5B ) .

Diagnosis.— Bufo (Anaxyrus) nevadensis is a member of the Great Basin B. boreas species complex ( Blair, 1972), but traditionally has been identified as B. boreas due to its occurrence within the Western Toad’s geographic range, yet

B. canorUS (S)

B. nelSoni 0.011

B. eXSUl 0.011 0.010

B. boreaS (CA) 0.030 0.031 0.027

B. williamSi 0.031 0.030 0.027 0.018

B. canorUS (N) 0.032 0.030 0.029 0.018 0.010

B. b. halophilUS 0.013 0.006 0.011 0.031 0.031 0.031

B. monfontanus 0.030 0.032 0.029 0.032 0.029 0.034 0.034

B. boreaS (OR) 0.028 0.029 0.024 0.004 0.016 0.016 0.029 0.031

B. boreaS (NV) 0.031 0.030 0.027 0.018 0.010 0.008 0.031 0.032 0.016

B. nevadensis 1 0.030 0.032 0.029 0.035 0.032 0.037 0.032 0.020 0.034 0.037

B. nevadensis 2 0.031 0.033 0.030 0.036 0.033 0.037 0.033 0.021 0.034 0.037 0.001

B. pUnctatUS 0.184 0.185 0.184 0.185 0.190 0.186 0.184 0.187 0.183 0.188 0.188 0.189 B. pUnctatUS 0.188 0.189 0.188 0.189 0.195 0.190 0.188 0.194 0.187 0.191 0.195 0.196 0.012

is distinct from B. boreas by a combination of morphological characters ( Figs. 2 , 6 , Tables 1, 4), genetic evidence ( Figs. 3 , 4 , Table 5), and restricted geographic distribution ( Fig. 5B ). Bufo nevadensis is distinguished from B. boreas due to its small adult body size ( SVL is approximately 2 cm smaller than B. boreas ; Tables 1, 4); significantly, but modestly longer head with a relatively shorter snout; well-separated, perceptibly short and narrow parotoid glands; significantly, but comparatively long legs, large hind feet ( Fig. 6B ); and distinctive mottling of venter ( Fig. 6B, D ).

Bufo nevadensis is among the smallest terrestrial bufonids within the B. boreas species complex ( Tables 1, 4). However, this new species exhibits a relatively large head unlike similarly small toads, B. exsul and B. monfontanus , new species, with a significantly, but comparatively shorter snout distinctive from all species within the complex except B. exsul ( Table 4). The well-separated and severely reduced parotoid glands exhibited in B. nevadensis is divergent from all taxa within the B. boreas species complex, and the shortened gland length distinguishes B. nevadensis from both B. boreas and B. monfontanus , new species. Bufo nevadensis has statistically significant, relatively long legs; longer femur than exhibited in B. exsul , B. monfontanus , new species, and B. williamsi , and a longer tibia and hind feet, which separate B. nevadensis from B. monfontanus , new species, and B. williamsi ( Table 4). In addition to morphological shape differences, B. nevadensis displays a dominantly brown and gray toned dorsum with prominent warts and heavily creased skin, which differs from B. exsul , B. monfontanus , new species, B. nelsoni , and B. williamsi . The venter of B. nevadensis is similar to B. exsul and B. williamsi , exhibiting black mottling contrasted against a white background color on the anterior sides of the limbs and belly. The presence of a dorsal stripe is extremely variable among individuals of B. nevadensis , as is similar to the other members of the B. boreas species complex, with the exception of B. exsul . Small, irregular tibial glands may be present in individuals, but this characteristic is highly variable.

In mature male B. nevadensis , distinct nuptial pads develop on the dorsal side of the first finger, a typical secondary sexual characteristic exhibited among most bufonids. This species lacks an advertisement call, but it emits a release call when males come in contact with one another which sound like the weeping of a chick and is similar among congeners of the B. boreas complex ( Stebbins, 2003).

Description of holotype.— Body relatively small and robust (SVL ¼ 62.5 mm); head wider (HW ¼ 20.1 mm) than long (HL ¼ 17.2 mm; 85% head length to head width). Snout subelliptical in dorsal view; snout profile moderately truncate in lateral view (SL ¼ 7.5 mm; 1.5 times longer than eye diameter). Canthus rostralis distinct and cuneate. Loreal region slightly concave. Nostrils slightly protuberant, direct- ed dorsolaterally, and closer to anterior corner of eye than to snout. Internarial distance (IND ¼ 3.8 mm) 75% of interorbital distance (IOD ¼ 4.8 mm). Eyes well separated; interorbital space nearly equivalent to eye diameter (ED ¼ 4.8 mm). Upper eyelids prominent in dorsal view; eyes slightly breach profile margin. Tympanum (TYM ¼ 3.0 mm) distinct, subovoid, relatively small (52% of eye diameter). Supratympanic fold present. Parotoid glands weakly present viewed above; parotoid glands narrow (PW ¼ 3.7 mm), severely tapered at posterior corner of eye in lateral view. Parotoid glands 1.5 times longer (PL ¼ 7.5 mm) than eye diameter; parallel, well separated (IPD ¼ 12.3 mm). Forearms robust. Fingers unwebbed; relative length III. I. II. IV; tips rounded, subarticular tubercles moderate, accessory palmar tubercles small, round. Inner metacarpal tubercle distinct, round. Palmar tubercle prominent, elliptical. Hind limbs long; femur slightly longer (FL ¼ 21.2 mm) than tibia (TL ¼ 18.7 mm). Tibial glands irregular, scarcely defined, half the length of parotoid gland. Tarsal fold present; hind feet webbed proximally (FTL ¼ 37.0 mm). Relative toe lengths IV. III. V. II. I; toe tips rounded. Subarticular tubercles faintly evident, small, round. Plantar tubercles numerous, small. Inner metatarsal tubercle pronounced, elevated, relatively large, elliptical. Outer metatarsal tubercle distinct, ovoid. Skin warty on dorsum; primary warts elevated, irregular; finely granular skin between elevated warts from interorbital space increasing in coarseness toward posterior margin of dorsum at articulation with femur. Hind limbs warty; tubercles small, moderate. Venter coarse, seat patch conspicuous.

Color in life.— Dorsal ground color of holotype light brownish gray, flecked with dark brown, irregular spotting ( Fig. 6A ). Grayish head dappled with dark brown patches, upper eyelids finely speckled black. Smooth dark olive brown blotches along prefrontal to frontal area of head and interorbital space. Pupil black, horizontal with gold streaked iris. Brownish gray parotoid glands exhibit minor black to dark brown spotting. Cream colored dorsal stripe present, originating posteriorly at nares and terminating at posterior margin of urostyle. Elevated, dark olive brown warts at interparotoid space, along dorsum; some warts set in black blotches; olive streaking connects warts along midline bordering dorsal strip; dorsolaterally, olive to dark brown wart color streaked against brownish gray background color. At midaxillary line, black streaking contrasts against white background. Throat white with minor black spotting near lower lip. Venter mottled black against white background color ( Fig. 6B ). In dorsal view, forelimbs have minor dark olive banding and olive patches against light grayish brown ground color; hind limbs exhibit dark olive brown banding and patches against light grayish brown ground color down to heavily dappled olive feet atop brownish gray background color. Along medial and ventral sides of hind limbs, black spotting and patches occur against white ground color down to medial edge of feet, which appear dark gray on underside.

Variation.— In paratypes, background color ranges from light gray to light brownish gray; warts may be olive colored to olive brown and may be set in black blotches. Brown to dark brown spotting around front of head; minor black spotting on throat and minor to heavy black mottling occur on venter.

Color in preservative.— Color is similar to that in life ( Fig. 6A, B ) with some notable differences. Overall background color in the holotype appears gray ( Fig. 6C ). Along dorsum, dark brown warts flattened and appear as heavy streaks against brownish gray background adjacent to dorsal stripe. Marbling along midaxillary line and venter less vibrant than in life and appear dark gray against white ground color and seat patch muted light gray ( Fig. 6D ).

Distribution.— Bufo nevadensis is known only to occur near and within the spring-fed wetland areas of Lockes Ranch (1,460 m above sea level), a protected wildlife management area located in Railroad Valley, an east-central desert basin between the Pancake Range and Grand Range of Nye County, Nevada ( Fig. 5B ). The critical marshland habitat for this endemic toad is solely fed from Big, Reynolds, and Hay Corral springs which results in a severely restricted range with an estimated distribution of 1.8 km 2. These outflows are remote and isolated, surrounded by cold desert habitat dominated by Big Sagebrush ( Artemisia tridentata ssp. tridentata ), Greasewood ( Sarcobatus vermiculatus ), Rubber Rabbitbrush ( Ericameria nauseosa ), and saltbush ( Atriplex spp. ) with limited usable corridors for amphibian dispersal, which likely restricts this species’ movement to other spring localities within Railroad Valley. Bufo nevadensis co-occurs with the federally listed threatened Railroad Valley Springfish, Crenichthys nevadae , and the Great Basin Spadefoot, Spea intermontana .

Life history and behavior.— Bufo nevadensis is nocturnal, emerging at dusk, and can be found in shallow water or among the vegetation in the perimeter band that transitions from riparian to sagebrush steppe habitat. Characteristic of cold deserts, Railroad Valley experiences extreme fluctuations in day and nighttime temperatures as well as season-to-season variation. As is common for other members of the B. boreas complex, these toads likely retreat to burrows in the fall, not emerging until spring, when males begin to congregate in shallow water for breeding. Mature males, similar to other members of the B. boreas complex (with the singular exception of B. canorus ), do not have an advertisement call, but emit a release call when males come in close contact with one another. Egg masses and tadpoles develop in still, shallow water amid the marshy vegetation of the wetland habitat.

The population size for this species is unknown; however, the extreme isolation and restricted range may indicate that the population numbers may be small. Little is known regarding the dispersal and non-breeding behavior of this rare toad.

Etymology.— The species name is a derivative from the state of Nevada ( U.S. A) where this rare toad occurs and pays homage to the unique biodiversity found in the desert landscape of its home state.

Remarks.— Railroad Valley is a geothermally active area within the Range and Basin Province with significant opportunities for anthropogenic energy production, including extraction of its oil reservoirs ( Liu et al., 1997) that continue to contribute to ongoing economic interests in the valley which are currently overseen by the Bureau of Land Management. Discovery of this rare new species should elicit high conservation concerns due to its severely restricted range and limitations to dispersal due to isolation and remoteness of the spring-fed habitat upon which B. nevadensis is dependent. Any further human anthropogenic modifications of habitat that may degrade this extremely important habitat would imperil this toad. However, with new species designation, conservation initiatives would provide a platform for ongoing policy and monitoring to allow this this endemic toad to persist.

Figures

FIG. 1. Sampling localities of congeneric taxa within the B. boreas species complex included for morphological (A) and DNA (B) collections within the hydrological Great Basin and surrounding states (Gordon et al., 2017). (A) Colors indicate species-specific populations measured for morphological analysis, with stars denoting new species. (B) Colors correspond with localized species and colors of B. boreas correspond with major mtDNA haplotype clades: W–Oregon and Western Great Basin (yellow), HL–Humboldt-Lahontan (blue), S–Mojave (aqua), and stars denote new species, which comprise the Eastern Great Basin clade (E). Maps created using ArcGIS software by ESRI (Environmental Systems Research Institute, 2011, ArcGIS Desktop: Release 10. Redlands, CA).

FIG. 2. Discriminant function analysis (DFA). Cross validated DFA using 14 size-corrected morphological characters measured from 518 live adult toads (Fig. 1A) examined within the hydrological Great Basin B. boreas species complex. Species identified as B. boreas (red), B. nelsoni (brown), B. exsul (dark green), B. williamsi (light blue), B. nevadensis (light green), and B. monfontanus (dark blue).

FIG. 3. Molecular examination of B. boreas species complex. (A) The TCS haplotype network was constructed using 257 sequences (1,622 bp) obtained from toad sampling (Fig. 1B) resulting in 62 unique haplotypes. Circle sizes correspond with the number of individuals of a particular haplotype. Major haplotype clades identified within B. boreas (W–Western Great Basin [yellow], HL–Humboldt-Lahontan [blue], and S–Mojave [aqua]) and to localized species (B. canorus [purple], B. exsul [tan], B. nelsoni [orange], B. williamsi [red]) and highlight the genetic divergence of both B. nevadensis (mauve) and B. monfontanus (brown). (B) Maximum likelihood tree derived from the control region of mitochondrial genome. Branches corresponding to partitions reproduced in less than 50% bootstrap replicates are collapsed. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (500 replicates) are shown next to the branches (Felsenstein, 1985). See Data Accessibility for tree file.

FIG. 4. Molecular phylogenetic reconstruction of region-wide B. boreas species complex diversity. Tree reconstruction included sequence data (Table 3) from B. boreas outside the Great Basin to evaluate the relationships between toads from Hot Creek and Railroad Valley and Utah and Colorado toads using the maximum likelihood method. Minor and major groups identified. Terminal ends include haplotype number and locality of collection. Sequences of B. boreas from outside the Great Basin (Table 3) include this taxon name within terminal end identifier. Minor groups include localized species within the Great Basin: B. nelsoni (green), B. exsul (orange), B. canorus (purple), B. williamsi (red), and newly delimited species, B. monfontanus (mauve) and B. nevadensis (pink), of the major group identified as the Eastern Great Basin clade (black bar). Two haplotypes of the root are shown. See Data Accessibility for tree file.

FIG. 5. Distribution of B. boreas and Great Basin B. boreas species complex. (A) The range-wide distribution of Bufo boreas shown in brown with hydrologic Great Basin outlined in black and hash mark interior within the western United States (Gordon et al., 2017). (B) Bufo boreas species complex and new species shown within hydrologic Great Basin, illustrating the small ranges of localized endemics. Spatial data for all toads except B. williamsi, B. nevadensis, and B. monfontanus provided by IUCN (2015). Images taken by M. R. Gordon except B. canorus, with photo credit to G. Nafis.

FIG. 6. Photographs of Bufo (Anaxyrus) nevadensis, new species, holotype (CAS 259272). Female toad in life: (A) dorsal view and (B) ventral view; and in preservative: (C) dorsal view and (D) ventral view. Photographs taken by M. R. Gordon.