Overview

Comprehensive Description

Description

R. onca has a snout-vent length between 44 and 87 mm, and is distinquished from similar species of the Rana pipiens complex by its short, indistinct, dorsolateral folds that extend 1/2 to 3/4 down the dorsum, generally shortened legs, an incomplete supralabial stripe, upper surfaces of the thighs usually spotted and not barred, and males having enlarged tympana, paired vocal sacs, and no vestigial oviducts. It has a dorsum which is brown, gray, or greenish above, with discrete greenish-brown spots that are usually reduced or faded on the front of the body. These dorsal spots are indefinitely bordered and are usually present on the upper surfaces of the thighs. Usually, the venter is whitish, and the throat has dark mottling. The groin and the undersides of the hind limbs are yellow to yellow-orange.

This is a minor success story. The species was long thought to be extinct or near extinction. Although extant populations have been found, they exist in isolated springs and creeks in desert environments, near reservoirs and recreation sites in an area that has rapidly urbanized. Accordingly, the species must be considered to be highly vulnerable. Jaeger et al. (2001) recommend development of a conservation management plan for the few remnant populations; such a conservation plan must prioritize the identification of habitat requirements and the reclamation of habitats necessary to maintain population viability.

  • Jennings, M. R. (1988). ''Rana onca Cope, relict leopard frog.'' Catalogue of American Amphibians and Reptiles. American Society of Ichthyologists and Herpetologists, 417.1-417.2.
  • Jaeger, J. R., Riddle, B. R., Jennings, R. D., and Bradford, D. F. (2001). ''Rediscovering Rana onca: evidence for phylogenetically distinct leopard frogs from the border region of Nevada, Utah, and Arizona.'' Copeia, 2001(2), 339-354.
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Distribution

Range Description

This species occurs on the border region of Arizona, Nevada, and Utah, USA, mostly below 1,000m asl. It was known from the Virgin and Muddy River drainages and along the Colorado River drainage downstream of its confluence with the Virgin River to Black Canyon below Lake Mead (Bradford, Jaeger and Jennings 2004, Bradford, Jennings and Jaeger 2005). In the late 1990s, the species could be found at seven sites in three general areas: a spring near Littlefield, Arizona, on the Virgin River; several springs along the Nevada side of the Overton Arm of Lake Mead; and within several springs in the Black Canyon along the Nevada side of the Colorado River (Jaeger et al. 2001; Bradford, Jaeger and Jennings 2004, Bradford, Jennings and Jaeger 2005). By 2001, two of these populations, including the one near Littlefield, had gone extinct (Bradford, Jaeger and Jennings 2004, Bradford, Jennings and Jaeger 2005).
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endemic to a single nation

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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: (250-1000 square km (about 100-400 square miles)) The known historical distribution includes springs, streams, and wetlands within the Virgin River drainage downstream from the vicinity of Hurricane, Utah; along the Muddy River, Nevada; and along the Colorado River from its confluence with the Virgin River downstream to Black Canyon below Lake Mead, Nevada and Arizona; all historical localities are at or within a few kilometers of these rivers, but this apparent restriction to the proximity of the main rivers may be partially an artifact of historical collecting activities (USFWS 2004). This species also may have occurred at lowland localities along the Colorado River upstream from the confluence with the Virgin River, but no known specimens exist from this area (Relict Leopard Frog Conservation Team 2005).

Relict leopard frogs are currently known to occur in two general areas in Nevada: near the Overton Arm area of Lake Mead, and Black Canyon below Lake Mead. Specimen records date back to 1936 at the Overton Arm area and to 1955 at Black Canyon. These two areas encompass maximum linear extents of only 3.6 and 5.1 kilometers, respectively (USFWS 2009). Relict leopard frog populations may possibly occur in other localized areas (USFWS 2009).

Two leopard frogs have been observed on different occasions in 2000 and 2001 at the fish hatchery at Willow Beach, Arizona, 10 km downstream from Bighorn Sheep Spring in Black Canyon; one of these frogs was collected and confirmed as R. onca based on mitochondrial DNA sequence similarity (C. Fiegel, pers. comm., 2001, cited by USFWS 2009). This individual was likely swept downstream from the occupied sites in Nevada.

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Distribution and Habitat

R. onca was found in creeks, springs, and seeps in the vicinity of Las Vegas Valley, Clark County, Nevada, and the Virgin River Valley, Washington County, Utah, at elevations between 370 and 760 m. Many of these populations are now extinct. Recent field work has discovered a few small populations in extreme northwestern Arizona along the Virgin River, from near Littlefield downstream to the Overton Arm of artificial Lake Mead. New populations have been discovered in springs that enter the Colorado River in Black Canyon, south of Hoover Dam in California.

  • Jennings, M. R. (1988). ''Rana onca Cope, relict leopard frog.'' Catalogue of American Amphibians and Reptiles. American Society of Ichthyologists and Herpetologists, 417.1-417.2.
  • Jaeger, J. R., Riddle, B. R., Jennings, R. D., and Bradford, D. F. (2001). ''Rediscovering Rana onca: evidence for phylogenetically distinct leopard frogs from the border region of Nevada, Utah, and Arizona.'' Copeia, 2001(2), 339-354.
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Physical Description

Size

Length: 8 cm

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Type Information

Holotype for Lithobates onca
Catalog Number: USNM 25331
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Sex/Stage: Female;
Preparation: Ethanol
Year Collected: 1872
Locality: No Further Locality Data, Utah, United States, North America
  • Holotype: Cope, E. D. 1872. Report upon Geographical and Geological Explorations and Surveys West of the Hundredth Meridian in Charge of First Lieutenant George M. Wheeler, Zoology. 528, plate 25, figures 1-3.
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
It occurs and reproduces in springs and outlet creeks, typically in or within a few meters of water, year round (Bradford, Jaeger and Jennings 2004, Bradford, Jennings and Jaeger 2005). It does not tolerate habitat disturbance.

Systems
  • Freshwater
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Habitat Type: Freshwater

Comments: Historically, this frog probably occupied a variety of habitats including springs, streams, and wetlands characterized by clean, clear water, in both deep and shallow water, and cover such as submerged, emergent, and perimeter vegetation (USFWS 2009). Leopard frogs generally require shallow water with emergent and perimeter vegetation for foraging and basking, and deeper water, root masses, undercut banks, and debris piles for cover and hibernacula (Relict Leopard Frog Conservation Team 2005). Emergent or submergent vegetation provides cover and egg-deposition substrate (Relict Leopard Frog Conservation Team 2005). Adults appear to prefer relatively open shorelines where dense vegetation does not dominate (Bradford et al. 2005). The recently extant populations inhabit spring systems with largely unaltered hydrology and no introduced American bullfrogs or game fishes (Bradford et al. 2004).

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Mojave Desert Habitat

This taxon is found in the Mojave Desert, the smallest of the four North American deserts. While the Mojave lies between the Great Basin Shrub Steppe and the Sonoran Desert, its fauna is more closely allied with the lower Colorado division of the Sonoran Desert. Dominant plants of the Mojave include Creosote Bush (Larrea tridentata), Many-fruit Saltbush (Atriplex polycarpa), Brittlebush (Encelia farinosa), Desert Holly (Atriplex hymenelytra), White Burrobush (Hymenoclea salsola), and Joshua Tree (Yucca brevifolia), the most notable endemic species in the region.

The Mojave’s warm temperate climate defines it as a distinct ecoregion. Mojave indicator species include Spiny Menodora (Menodora spinescens), Desert Senna (Cassia armata), Mojave Indigobush (Psorothamnus arborescens), and Shockley's Goldenhead (Acamptopappus shockleyi). The Mojave supports numerous species of cacti, including several endemics, such as Silver Cholla (Opuntia echinocarpa), Mojave Prickly Pear (O. erinacea), Beavertail Cactus (O. basilaris), and Cotton-top Cactus (Echinocactus polycephalus).

While the Mojave Desert is not so biologically distinct as the other desert ecoregions, distinctive endemic communities occur throughout. For example, the Kelso Dunes in the Mojave National Preserve harbor seven species of endemic insects, including the Kelso Dunes Jerusalem Cricket (Ammopelmatus kelsoensis) and the Kelso Dunes Shieldback Katydid (Eremopedes kelsoensis). The Mojave Fringe-toed Lizard (Uma Scoparia), while not endemic to the dunes, is rare elsewhere. Flowering plants also attract butterflies such as the Mojave Sooty-wing (Pholisora libya), and the widely distributed Painted Lady (Vanessa cardui).

There are a total of eight amphibian species present in the Mojave Desert all of which are anuran species: the endemic Relict Leopard Frog (Lithobates onca); the endemic Amargosa Toad (Anaxyrus nelsoni); Lowland Leopard Frog (Lithobates yavapaiensis); Red-spotted Toad (Anaxyrus punctatus); Southwestern Toad (Anaxyrus microscaphus); Great Basin Spadefoot (Spea intermontana); Great Plains Toad (Anaxyrus cognatus); and the Pacific Treefrog (Pseudacris regilla).

The native range of California’s threatened Desert Tortoise (Gopherus agassizii) includes the Mojave and Colorado Deserts. The Desert Tortoise has adapted for arid habitats by storing up to a liter of water in its urinary bladder. The following reptilian fauna are characteristic of the Mojave region in particular: Gila Monster (Heloderma suspectum NT); Western Banded Gecko (Coleonyx variegatus), Northern Desert Iguana (Dipsosaurus dorsalis), Western Chuckwalla (Sauromalus obesus), and regal horned lizard (Phrynosoma solare). Snake species include the Desert Rosy Boa (Charina trivirgata gracia), Mojave Patchnose Snake (Salvadora hexalepis mojavensis), and Mojave Rattlesnake (Crotalus scutulatus).

Endemic mammals of the ecoregion include the Mojave Ground Squirrel (Spermophilus mohavensis) and Amargosa Vole (Microtus californicus scirpensis); and the California Leaf-nosed Bat (Macrotus californicus).

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Migration

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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Trophic Strategy

Comments: Adults probably are mainly invertivorous. Larvae probably eat algae, organic debris, plant tissue, and minute organisms in water.

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 1 - 5

Comments: The species is extant in only five locations in two general areas (Bradford et al. 2004, USFWS 2009). It occurs in multiple specific sites in each location. As of 2008, 13 sites (8 natural and 5 translocation sites) supported relict leopard frogs (egg masses observed at 10 of 13 sites) (USFWS 2009).

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Global Abundance

1000 - 2500 individuals

Comments: An estimate for the total number of frogs at all sites, based on mark-recapture data, visual encounter surveys, and extent of habitat, was approximately 1,100 adults (range 693-1,833) (Bradford et al. 2004)..

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Life History and Behavior

Cyclicity

Comments: These frogs are inactive in cold temperatures. Most activity occurs at night.

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Reproduction

Information is incomplete due to inadequate study; eggs have been found in November and February; calling has been heard in February, June, November (Jennings et al. 1995). Individuals reach sexual maturity in 1-2 years, and some likely live 4-5 years or more.

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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
EN
Endangered

Red List Criteria
B2ab(v); C2a(i)

Version
3.1

Year Assessed
2004

Assessor/s
Jef Jaeger, David Bradford, Geoffrey Hammerson

Reviewer/s
Global Amphibian Assessment Coordinating Team (Simon Stuart, Janice Chanson, Neil Cox and Bruce Young)

Contributor/s

Justification
Listed as Endangered because its Area of Occupancy is less than 500km2, with all individuals in fewer than five locations, and the number of mature individuals in Arizona, Nevada and Utah is declining; and because its population size is estimated to number fewer than 2,500 mature individuals, there is an observed continuing decline in the number of mature individuals, and no subpopulation contains more than 250 mature individuals.

History
  • 1996
    Vulnerable
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National NatureServe Conservation Status

United States

Rounded National Status Rank: N1 - Critically Imperiled

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NatureServe Conservation Status

Rounded Global Status Rank: G1 - Critically Imperiled

Reasons: This frog occupies only 10-20 percent of the historical range and currently occurs in 8 natural and 5 translocation sites in Nevada. Primary threats include water diversions and developments, the presence of non-native predators and competitors, loss and fragmentation of habitat, and low numbers of individuals in metapopulations. Currently, no specific water developments or direct habitat losses are known that could result in impacts to the species, and the numbers of individuals and sites occupied by the frog are increasing through captive-rearing and translocation.

Intrinsic Vulnerability: Moderately vulnerable

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Current Listing Status Summary

Status: Candidate
Date Listed:
Lead Region:   California/Nevada Region (Region 8) 
Where Listed:


For most current information and documents related to the conservation status and management of Lithobates onca, see its USFWS Species Profile

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Population

Population
As of 2001, there were five known sites in two general areas containing reproducing populations of leopard frogs (Jaeger et al. 2001; Bradford, Jaeger and Jennings 2004, Bradford, Jennings and Jaeger 2005). A rough estimate of the total population size (combining all sites) was approximately 1,100 adults (range 693-1,833), most of which were at a single spring (Bradford, Jaeger and Jennings 2004, Bradford, Jennings and Jaeger 2005).

Population Trend
Decreasing
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Global Short Term Trend: Relatively stable to decline of 30%

Comments: Two of seven populations that were extant in the 1990s have been extirpated (Bradford et al. 2004).

Global Long Term Trend: Decline of 70-90%

Comments: USFWS (2009) estimated that the current distribution is approximately 10 to 20 percent of the historical distribution.

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Life History, Abundance, Activity, and Special Behaviors

The fully developed tadpoles reach 85 mm in length and have a greenish olive dorsum, a heavily mottled, pale green-yellow tail, and a light venter. Labial teeth are 2/3 or 1/3 with the second upper row short or absent.

  • Jennings, M. R. (1988). ''Rana onca Cope, relict leopard frog.'' Catalogue of American Amphibians and Reptiles. American Society of Ichthyologists and Herpetologists, 417.1-417.2.
  • Jaeger, J. R., Riddle, B. R., Jennings, R. D., and Bradford, D. F. (2001). ''Rediscovering Rana onca: evidence for phylogenetically distinct leopard frogs from the border region of Nevada, Utah, and Arizona.'' Copeia, 2001(2), 339-354.
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Threats

Major Threats
The causes of the decline of this species are not entirely clear, but the loss of habitat to agriculture and water development were likely causes, as was the introduction of American bullfrogs (Rana catesbeiana), crayfish, and exotic predatory fish (Jennings 1988). These factors remain active threats. Vegetation encroachment, of both exotic and native vegetation, has been suspected of causing recent declines (Bradford, Jaeger and Jennings 2004).
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Degree of Threat: Very high - high

Comments: The causes of the decline are not entirely clear, but suggested factors include alteration of aquatic habitat due to agriculture and water development, and the introduction of exotic predators and competitors (Jennings 1988, Jennings and Hayes 1994). The formation of Lake Mead in 1935 and Lake Mojave in 1951 inundated many river miles and adjacent associated wetlands and fragmented some of the remaining populations (USFWS 2009). Connectivity among the extant populations has almost certainly been dramatically reduced as a result of damming the Colorado River (USFWS 2009). The reduction in connectivity is a result of a wider waterbody created when the Colorado River was dammed, thus preventing frogs from moving from one side of the river to the other. Lake Mohave influences the river level such that the canyon floor is never exposed, predatory game fishes are present in the river, and water is continually cool as it emerges from Lake Mead (USFWS 2009). Moreover, wetland habitat has been converted to agriculture or urban development near the Virgin and Muddy Rivers in Utah, Arizona, and Nevada (USFWS 2004). Also, along the Virgin River, the hydrological regime has been substantially changed by upstream impoundments, diversions, and ground water pumping (BIO-WEST, Inc., 2001; USFWS 2009).

Two recent population extinctions occurred concomitantly with encroachment of emergent vegetation into pools; this may have occurred as a result of natural processes in one case, and anthropogenic processes in the other (Bradford et al. 2004).

Exotic species, which are often implicated as serious predators and competitors of native ranid frogs in the western U.S., have become widely distributed along the Virgin, Muddy, and Colorado Rivers. Included among these are the American bullfrog, many species of exotic fishes, and red swamp crayfish (Procambarus clarkii) (Jennings and Hayes 1994). These species potentially prey on all life stages of the relict leopard frog. Bullfrogs also negatively impact native amphibians through competition for prey and coversites. Crayfish and exotic fishes may be important predators on eggs and larvae of relict leopard frogs. [from USFWS 2002]

The relict leopard frog is further threatened by the low numbers of individuals within each population, some of which may not be viable. Amphibians are thought to have a metapopulation structure (i.e., groups of individuals inhabiting a system of habitat patches connected by migration across contiguous habitat). Populations that occur in isolated patches may be extirpated by stochastic events such that recolonization may not occur due to the distance of separation and absence of contiguous habitat. Genetic drift and inbreeding depression may also occur as a result of restricted gene flow associated with small, isolated populations, thus further threatening their persistence. [from USFWS 2002]

Chytridiomycosis, a fungal disease associated with population declines of various amphibian species, although not yet confirmed as a pathogen of relict leopard frogs, must be regarded as a potential threat.

Extirpations

Between 1991 and 1995, habitat change was conspicuous at Corral Springs. The pools that were initially largely open with scattered emergent vegetation became choked with emergent vegetation, primarily native Scirpus spp. By early summer of 1994, most of these pools had virtually no open water. Extirpation of leopard frogs from this site may have been the result of natural processes, because individuals may periodically colonize this site from Rogers Spring during wet periods after the site is scoured by flood waters, and populations may subsequently be extirpated due to shrinkage of aquatic habitat and vegetation encroachment as drier conditions prevail. The demise of the relict leopard frog at Corral Spring may also have been facilitated by the construction of a fence in 1991 to exclude feral burros from most of the site, an action that encouraged overgrowth of emergent vegetation. [from USFWS 2002]

As at Corral Spring, the demise of the population at Littlefield occurred concomitantly with loss of pool habitat due to rapid encroachment of emergent vegetation. Between 1992 and 2001, vegetation cover (primarily Scirpus spp.) had increased dramatically such that no pools of open water remained exposed except for the artificial pond. This rapid encroachment may have resulted from anthropogenic processes. Historically, prior to the establishment of reservoirs in the Virgin River watershed, the emergent vegetation at the Littlefield site would have been scoured periodically by flooding of the Virgin River. Until some years ago, vegetation in part of this area was kept open by light to moderate livestock grazing. Subsequently, with the absence of both flood action and grazing, emergent vegetation grew over virtually all the former open water at the site. Moreover, introduced bullfrogs, which may prey on the relict leopard frog, have become established in wetlands along this portion of the Virgin River (BIO-WEST, Inc., 2001). [from USFWS 2002]

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Life History, Abundance, Activity, and Special Behaviors

R. onca once occurred at the edge of the ranges of R. chiricahuensis, R. pipiens, and R. yavapaiensis, and survived as a relict population in the marginal habitat of desert springs and creeks. However, since 1920 there have been severe habitat alterations as well as introductions of non-native fish and amphibians into these habitats, which pushed R. onca populations into decline. The last known specimens from Utah were collected in 1950 from Berry Springs, Washington County. Extant populations are small and highly vulnerable.

  • Jennings, M. R. (1988). ''Rana onca Cope, relict leopard frog.'' Catalogue of American Amphibians and Reptiles. American Society of Ichthyologists and Herpetologists, 417.1-417.2.
  • Jaeger, J. R., Riddle, B. R., Jennings, R. D., and Bradford, D. F. (2001). ''Rediscovering Rana onca: evidence for phylogenetically distinct leopard frogs from the border region of Nevada, Utah, and Arizona.'' Copeia, 2001(2), 339-354.
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Management

Conservation Actions

Conservation Actions
Remaining populations occur within the Lake Mead National Recreation area. A range-wide conservation assessment and strategy is currently being developed by a working group consisting of representatives from federal, state, and local governmental agencies, as well as specialist representatives. Current conservation measures include the re-introduction of this frog to suitable, unoccupied locations, and in 2002 frogs were released at two unoccupied natural spring sites.
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Management Research Needs: Habitat conditions required for long-term survival need to be determined, as does the importance of bighorn sheep and burros in maintaining favorable habitat (Jennings et al. 1995).

Biological Research Needs: See management summary.

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Needs: See management summary.

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Relevance to Humans and Ecosystems

Risks

Stewardship Overview: Recent conservation activities included the following (USFWS 2009): Maintaining frog-rearing facilities at the Willow Beach National Fish Hatchery. Planning for a relict leopard frog habitat project at the Willow Beach National Fish Hatchery. Augmenting six existing translocation sites (Goldstrike Canyon; Grapevine Spring, Arizona; Lower Grapevine Spring, Nevada; Pupfish Refuge, Black Canyon, Nevada; Red Rock Spring, Nevada (east of Overton Arm); and Tassi Spring, Arizona). Monitoring all translocated and natural populations. Enhancing habitat at the Pupfish Refuge and Salt Cedar Spring sites in Black Canyon. Working with conservation partners to establish a refugium near the Muddy River. Working with the Nevada Division of State Parks (NDSP) to develop an agreement to establish a refuge at Ash Grove Spring (Spring Mountain Ranch State Park). Finishing a GIS database of natural, transplanted, and potential sites. Beginning the implementation of three Clark County Multiple Species Habitat Conservation Plan (MSHCP) proposals: delineation of distribution, evaluation of relatedness, and assessment of connectivity for relict leopard frog populations; relict leopard frog monitoring and management; evaluation of experimental habitat manipulations on relict leopard frog populations. Investigating new translocation sites in Black Canyon and Gold Butte. Continuing to plan for a refuge site at the Las Vegas Springs Preserve. Investigating the potential for a water pumping station as a relict leopard frog site. Working with the NPS Data Management Team to ensure timely distribution of work products to the Conservation Team. Incorporating relict leopard frog conservation priorities into the Virgin River Habitat Conservation and Recovery Plan. Assessing chytrid fungus pathogen status in relict leopard frogs. Clearing Union Pass Spring and Quail Spring for translocation. Following up on Stuart Ranch and Pakoon Springs as potential translocation sites.

Recommended conservation measures include the following (USFWS 2009): 1. Remove or substantially minimize threats to extant populations and occupied habitats. 2. Enhance existing habitat and/or create new habitats where feasible. 3. Establish additional populations of relict leopard frogs in existing or created habitats. 4. Manage relict leopard frogs and their habitats to ensure persistence in diverse aquatic ecosystems, and facilitate processes that promote self-sustaining populations. 5. Monitor relict leopard frog populations. 6. Investigate the conservation biology of the relict leopard frog, and use the results of such investigations to better meet the goal and objectives.

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Relation to Humans

The species was once common in the springs of Las Vegas, Nevada, where it was described as a distinct species (R. fisheri). Springs have been developed for human use, including domestic water, animal husbandry, and recreation (hot springs). Many springs were inundated by the construction of Hoover Dam and the rising of Lake Mead.

  • Jennings, M. R. (1988). ''Rana onca Cope, relict leopard frog.'' Catalogue of American Amphibians and Reptiles. American Society of Ichthyologists and Herpetologists, 417.1-417.2.
  • Jaeger, J. R., Riddle, B. R., Jennings, R. D., and Bradford, D. F. (2001). ''Rediscovering Rana onca: evidence for phylogenetically distinct leopard frogs from the border region of Nevada, Utah, and Arizona.'' Copeia, 2001(2), 339-354.
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Names and Taxonomy

Taxonomy

Comments: Vegas Valley leopard frog, R. fisheri, (now considered extinct) previously was regarded as a subspecies of R. onca. Jennings et al. (1995) conducted morphological comparisons and concluded that R. fisheri and R. onca are distinct species. Jaeger et al. (2001) examined variation in mtDNA and morphology and concluded that certain leopard frog populations in the Virgin River/Black Canyon (Colorado River) region represent a species (R. onca) distinct from the lowland leopard frog (R. yavapaiensis).

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Source: NatureServe

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