Bufo (Anaxyrus) monfontanus, 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 : 2030-2032

Bufo (Anaxyrus) monfontanus , new species urn:lsid:zoobank.org:act:58EA3AB0-7EF3-4CF3-B832-5938DF05021C

Hot Creek Toad

Figures 1–4 , 5B , 7 ; Tables 1, 4–5

Holotype.— CAS 259273 , adult male ( Fig. 7 , Tables 1, 4), United States, Nevada, Nye County, Hot Creek Canyon, 38832 0 19.32 00 N, 116827 0 32.9 00 W, M. R. Gordon , 6 May 2015.

Paratypes.— UNR 7910 , adult male ; UNR 7911 , adult male ; UNR 7912 , adult male ; UNR 7913 , adult male ; UNR 7914 , adult male ; UNR 7915 , adult male ; UNR 7916 , adult male ; UNR 7917 , adult male; all individuals collected within the identified home range, Hot Creek Canyon, 38832 0 19.32 00 N, 116827 0 32.9 00 W ( Fig. 5B ), M . R. Gordon , 6 May 2015 .

Diagnosis.— Bufo (Anaxyrus) monfontanus occurs within the range of B. boreas but is distinct from the Western Toad by a combination of diagnostic morphological characters ( Figs. 2 , 7 , Tables 1, 4), genetic evidence ( Fig. 3 , Table 5), and restricted geographic distribution ( Fig. 5B ). Bufo monfontanus is distinguishable from B. boreas by having a small adult body size ( SVL is 2 cm smaller than B. boreas ; Tables 1, 5); significantly, but modestly shorter head; perceptibly large, parotoid glands; significantly, but comparatively shorter legs with small hind feet; and weakly warted body ( Fig. 7A ).

Bufo monfontanus is among the smallest bufonids within the B. boreas species complex, and it is only larger than B. williamsi ( Tables 1, 4). Bufo monfontanus has a significant, but relatively shorter head with a comparatively long snout, with a relative head width more comparable to larger-sized taxa B. boreas and B. nelsoni ( Table 4). An important diagnostic feature among B. monfontanus is the presentation of welldefined, relatively large parotoid glands, which distinguishes this small toad from all other small-sized toads within the B. boreas species complex ( Table 4). Bufo monfontanus has shorter legs; significantly, but relatively the shortest femur and tibia of all taxa within the B. boreas species complex and relatively small feet distinct from both B. boreas and B. nevadensis ( Table 4). The dorsal stripe is extremely variable among individuals of B. monfontanus ; a characteristic typical among taxa within the B. boreas species complex with the exception of B. exsul . Small, irregular tibial glands may be present among individuals of B. monfontanus as seen in both B. nevadensis and B. williamsi .

In adult male B. monfontanus , distinct nuptial pads develop on the dorsal side of the first finger which is a typical secondary sexual characteristic exhibited among most bufonids. Akin to congeners of the B. boreas species complex, except B. canorus , males of this species emit a release call that sounds like a weeping chick ( Stebbins, 2003).

Description of holotype.— Body small, robust (SVL ¼ 59.6 mm); head wider (HW ¼ 19.3 mm) than long (HL ¼ 16.2 mm). Snout subovoid in dorsal view; snout rounded in lateral view, long (SL ¼ 6.4 mm; 40% of head length). Canthus rostralis distinct, concave, angular, sloping up to medial orbital margins. Loreal region slightly concave. Nostrils protuberant, directed dorsolaterally, closer to anterior corner of eye than end of snout. Internarial distance 75% of eye-to-naris distance (IND ¼ 2.3 mm). Relatively moderate eyes well separated (ED ¼ 4.4 mm; IOD ¼ 3.8 mm); eyes do not breach snout profile in dorsal view. Tympanum distinct, oval, small (TYM ¼ 2.5 mm; 53% of eye diameter). Supratympanic fold weakly present, flat. Parotoid glands longer (PL ¼ 8.8 mm) than wide (PW ¼ 5.3 mm; length nearly twice eye diameter). Glands elevated, slightly convergent at posterior ends in dorsal view. In lateral view, parotoid glands elongated longitudinally from posterior corner of eye, oval, wider than the eye (1.4 times eye diameter). Interparotoid space large (IPD ¼ 9.4 mm; 2.5 times interorbital distance). Forearms robust, smooth. Fingers unwebbed; relative lengths III. I. IV. II; nuptial pads present, raised on dorsal side of digit I; tips rounded, subarticular tubercles moderate, round; accessory palmar tubercles small, round. Inner metacarpal tubercle raised, prominent, round. Palmar tubercle distinct, large, subovoid, borders medial margin of inner metacarpal tubercle. Hind limbs long; femur longer (FL ¼ 23.1 mm) than tibia (TL ¼ 19.7 mm). Tibial gland weakly present in dorsal view and equivalent to the width of the parotoid gland. Tarsal fold present. Hind feet webbed proximally (FTL ¼ 35.0 mm). Relative toe lengths IV. III. V. II. I; tips rounded. Subarticular tubercles distinct, small and round; plantar tubercles numerous, small. Inner metatarsal tubercle conspicuous, elevated, relatively large and elliptical. Outer metatarsal tubercle pronounced, ovoid. Longitudinally along dorsum, dorsal stripe weakly present, originating posterior to interorbital space, terminating at urostyle; irregular, elevated but scattered warts present, increasing in size from interorbital space to posterior margin of urostyle. Skin between warts nearly smooth; forearms smooth; hind limbs exhibit minor warts, tibial gland scarcely present and irregular. Originating posterior to labial commissure, inferior to tympanum, dense, small tubercles occur along posterior axillary line, terminating near anterior articulation of femur. Venter coarse; seat patch granular and conspicuous.

Color in life.— Dorsal background color light olive gray with minor black flecks throughout dorsum; elevated brown warts encircled by narrow, incomplete black border ( Fig. 7A ). More pronounced black rings border brown warts laterally along posterior axillary line. Dorsal stripe present; fine line, light green, interrupted at parotoid region. Pupils horizontal; iris flecked gold. Parotoid glands flecked with black, minute spots against olive gray. Thick brown stripe present, inferior to eye, occurring from orbit anterior border down to upper lip margin; buffy colored tubercles originate at labial commissure, transition to more olive colored spines moving laterally along body. Along midaxillary line, olive background color transitions to cream color with heavy black blotching. Throat clear, buffy colored. Venter nearly clear, buffy with minor black spots except at seat patch, which is gray and coarse with fine white granules ( Fig. 7B ). Dorsally, forelimbs exhibit little color variation from olive with some minor dark brown patches; hind limbs have minor black stripes atop white background color along inner shank down to dorsal side of foot.

Variation.— In paratypes, dorsal stripe present or weakly present; dorsum ground color variable shades of olive; venter may exhibit minor black spotting against buffy ventral ground color. Parotoids directed parallel behind eyes or slightly convergent at posterior ends. Brown striping above lip and inferior to eyes may be weakly present.

Color in preservative.— There are notable differences in preservation ( Fig. 7C, D ) when compared in life ( Fig. 7A, B ). Overall ground color of preserved holotype is dark and gray. Dorsal stripe thin, white, broken at posterior edges of parotoid glands, continues to vent. Warts along dorsum flattened, dark gray, and similar in shade to ground color and parotoid glands. Head dark gray, striping inferior to eye muted and tubercles posterior to labial commissure appear white. Arms very smooth and dark. Nuptial pads present and brown in preservative. Marbling along midaxillary line black against muted gray ground color. Venter light gray overall; seat patch muted in preservative. Tubercles on feet and hands diminished and dark, tips appear brown.

Distribution.— Bufo monfontanus is only found within the marshes fed by thermal spring outflows in Hot Creek Canyon (1,859 m above sea level) in Hot Creek Range in Central Nevada. The narrow canyon is nestled between Box and Corral Canyons and runs east to west, and toads have only been found in the small Hot Creek stream fed by Upper Warm Springs. This locality is extremely remote and isolated, and the spring flows through the canyon are interrupted, likely restricting toad dispersal from east to west, with few suitable corridors outside the canyon. The estimated range for B. monfontanus is extremely small at 1 km 2, as essential wetland habit is critically limited and isolated by cold desert habitat dominated by sagebrush steppe. The population size is unknown for this endemic toad, but is likely small and warrants further examination. Bufo monfontanus co-occurs with introduced Crenichthys nevadae (Railroad Valley Springfish) near Upper Warm Springs, and the introduced Rana catesbeiana (American Bullfrog) can be found within the interior streams of the canyon.

Life history and behavior.— Bufo monfontanus emerges only after dusk, exhibiting typical nocturnal behavior similar among taxa of the B. boreas species complex with the exception of B. canorus , which is diurnal. This species can be found in the marshy water or in the perimeter band that transition from riparian habitat to sagebrush steppe. Typical of other species in the B. boreas species complex, B. monfontanus likely hibernates, using burrows. Little is known about the dispersal behavior of this toad. The high elevation and extreme temperatures, both daily and season-to-season variability, likely prohibit a long breeding season, and further investigation through monitoring and annual surveys could provide insight into the life history strategy of this unique toad.

Etymology.— The species name monfontanus (from the Latin ‘‘mons’’ for mountain and Latin ‘‘fons,’’ a spring or fountain) is descriptive of the high-elevation spring habitat where this toad occurs and pays tribute to the nature of the rare spring habitat and the biodiversity relying on this important resource within the Nevada.

Remarks.— This new toad species, similar to other taxa of the B. boreas species complex, represents another narrow endemic that is found only in small and fragile spring ecosystems of the Great Basin. This new species warrants high conservation concern and urgent initiatives to monitor and to study how to preserve this new toad species. Especially troubling is that little is known about the population size, breeding, and dispersal of this small toad species. Additionally, the predatory generalist Rana catesbeiana co-occurs within the spring-fed stream system of Hot Creek Canyon, and this species is known to outcompete and prey upon much smaller anurans such as bufonids. Rana catesbeiana is also a known vector for potentially lethal anuran diseases, such as chytridiomycosis ( Kats and Ferrer, 2003; Daszak et al., 2004), whose effects on the narrowly distributed B. monfontanus is unknown.

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. 7. Photographs of Bufo (Anaxyrus) monfontanus, new species, holotype (CAS 259273). Male 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.