This frog is a member of the mountain yellow-legged frog complex which is comprised of two species: Rana muscosa and Rana sierrae. Both species are highly aquatic and are always found within a meter or two from the edge of water. Rana sierrae is yellowish or reddish brown from above, with black or brown spots or lichen-like markings. Toe tips are usually dusky. Underside of hind legs and sometimes entire belly is yellow or slightly orange, usually more opaque than in foothill yellow-legged frog, Rana boylii. Yellow often extends forward to level of forelimbs. Dorsolateral folds present but frequently indistinct. The tadpoles are black or dark brown and are large (total length often exceeds 10 cm) and metamorphose in 1-4 years depending on the elevation.
Rana sierrae differs from Rana muscosa in having relatively shorter legs. When a leg is folded against the body the tibio-tarsal joint typically falls short of the external nares. The mating call of R. sierrae is significantly different from that of R. muscosa in having transitions between pulsed and noted sounds. Both species call underwater. Males can be heard above water but only from a short distance away (<2 meters). The two species also differ in mitochondrial DNA. The mitochondrial DNA, male advertisement calls, and morphology datasets are geographically concordant (Vredenburg et al. 2007).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: United States
U.S. state distribution from AmphibiaWeb's database: California, Nevada
This montane species once occurred in California and Nevada, USA but is now extinct in the state of Nevada. Rana sierrae ranges from the Diamond Mountains northeast of the Sierra Nevada in Plumas County, California, south through the Sierra Nevada to the type locality, the southern-most locality at Matlock Lake just east of Kearsarge Pass (Inyo County, California). In the extreme northwest region of the Sierra Nevada, several populations occur just north of the Feather River, and to the east, there was a population on Mt. Rose, northeast of Lake Tahoe in Washoe County, Nevada, but, as mentioned above, it is now extinct. West of the Sierra Nevada crest, the southern part of the R. sierrae range is bordered by ridges that divide the Middle and South Fork of the Kings River, ranging from Mather Pass on the John Muir Trail east to the Monarch Divide. East of the Sierra Nevada crest, R. sierrae occurs in the Glass Mountains just south of Mono Lake (Mono County, CA) and along the east slope of the Sierra Nevada south to the type locality at Matlock Lake (Inyo County, CA).
Life History, Abundance, Activity, and Special Behaviors
Similar to R. muscosa, breeding begins soon after ice-melt or early in spring and can range from April at lower elevations to June and July in higher elevations (Wright and Wright 1949; Stebbins 1951; Zweifel 1955). Eggs are deposited underwater in clusters attached to rocks, gravel, and under banks, or to vegetation in streams or lakes (Wright and Wright 1949; Stebbins 1951; Zweifel 1955). Livezey and Wright (1945) report an average of 233 eggs per mass(n=6, range 100-350). Eggs contain a vitelline capsule, and three gelatinous envelopes, all clear and transparent (see illustrations in: Stebbins 2003). In laboratory breeding experiments egg hatching times ranged from 18-21+ days at temperatures ranging from 5-13.5 °C (Zweifel 1955).
The length of the larval stage depends upon the elevation. At lower elevations where the summers are longer, tadpoles are able to grow to metamorphosis in a single season (Storer 1925). At higher elevations where the growing season can be as short as three months, tadpoles must overwinter at least once and may take 2 or 4 years of growth before they are large enough to transform (Wright and Wright 1949; Zweifel 1955).
Trends and Threats
Rana sierrae is critically endangered, along with its sister species Rana muscosa. These frogs have declined dramatically despite the fact that most of the habitat is protected in National Parks and National Forest lands. A study that compares recent surveys (1995-2005) to historical localities (1899-1994; specimens from the Museum of Vertebrate Zoology and the California Academy of Sciences) found that 92.5% of populations have gone extinct (11 remaining out of 146 sites; Vredenburg et al. 2007).
The two most important factors leading to declines in R. sierrae and R. muscosa are disease and introduced predators.
Introduced trout prey on R. sierrae (Needham and Vestal 1938; Mullally and Cunningham 1956)and have been implicated in a number of studies as one of the sources of decline (Bradford 1989; Bradford et al. 1993; Jennings 1994; Knapp 1996; Drost and Fellers 1996; Knapp and Matthews 2000). In fact, as early as 1915 Joseph Grinnell and his field crews (Grinnell and Storer 1924) noticed that Rana sierrae rarely survived in lakes where trout were planted. Whole lake field experiments have shown that when non-native trout are removed, both Rana sierrae and Rana muscosa populations rebound (Vredenburg, 2004; Knapp et al. 2007).
While it is clear that introduced trout negatively affect R. sierrae and R. muscosa mainly through predation on tadpoles, trout also compete for resources with adult frogs. A food web study that used stable isotopes to trace energy through the Sierran lake food webs concluded that introduced trout are superior competitors and suppress the availability of large aquatic insects that make up a major portion of the diets of adult frogs (Finlay and Vredenburg 2007).
A lethal disease, chytridiomycosis, caused by an aquatic fungal pathogen Batrachochytrium dendrobatidis, or Bd (Berger et al. 1998) has caused population extinctions in R. muscosa and R. sierrae in the Sierra Nevada (Rachowicz et al. 2006). Long-term studies reveal that infection intensity is key; once a critical threshold of Bd fungal infection is reached, death ensues (Vredenburg et al. 2010). Population extirpation is the most common outcome, but a few mountain yellow-legged frog (Rana sierrae and Rana muscosa) populations have survived in low numbers. Modeling shows that chytriodiomycosis outcome at the population level (extirpation vs. persistence) can result solely from density-dependent host-pathogen dynamics, which may hold for other wildlife diseases as well (Briggs et al. 2010). In an effort to rescue the last surviving frogs, the Vredenburg lab is treating adult Rana sierrae in the field with anti-fungal medication; frogs are bathed for five minutes daily over the course of a week (Lubick 2010).
Other possible causes for decline in R. sierrae include air pollution (pesticide drift; Davidson et al. 2002; Davidson 2004), UV-B radiation, and long term changes in weather patterns, especially concerning the severity and duration of droughts. Acidification from atmospheric deposition has been suggested as another cause, but Bradford et al. (1994) found no evidence to support this hypothesis.
For more information on active research on this species please see:
Relation to Humans
Mountain yellow-legged frogs (the amphibian species complex including both Rana muscosa and Rana sierrae) were once the most common vertebrates in the high elevation Sierra Nevada. Documented historical accounts go back to the turn of the last century (1915) from surveys conducted by Joseph Grinnell and Tracy Storer (published in 1924) from the University of California's Museum of Vertebrate Zoology. Joseph Grinnell was instrumental in the foundation of Yosemite National Park, one of the jewels of the American National Park Service.
Possible reasons for amphibian decline
Predators (natural or introduced)
This species was featured as News of the Week on 17 October 2016:
Nearly all of the reports on global patterns of amphibian extinction and decline have been bad news, with hundreds of species lost and thousands in jeopardy. A new report in PNAS (Knapp et al. 2016) shows a regional pattern of recovery across hundreds of populations in Yosemite National Park for a charismatic species, the Sierra Nevada Yellow-legged frog. The study is based on >7,000 frog surveys over a 20-year period and showed recovery despite ongoing stressors such as disease and introduced predatory fish. Results from a laboratory experiment indicate that these increases may be in part because of reduced frog susceptibility to chytridiomycosis, but the cessation of fish stocking also contributed to the recovery. Continuing studies will determine if local extinction sites become repopulated (Written by Vance Vredenburg).
This species was featured as News of the Week on 24 October 2016:
Major habitat restoration moves ahead for two endangered montane frogs in California. After years of review and planning, the National Park Service (USA) is officially moving forward with major plans to restore high elevation aquatic ecosystems in the Sequoia and Kings Canyon National Parks in the Sierra Nevada of California. These actions will help recover two endangered montane frogs, the Sierra Nevada yellow-legged frog (Rana sierrae) and the Sierra Madre or Southern Mountain yellow-legged frog (Rana muscosa). These significant conservation actions, based in part on results from a 2004 field experiment (Vredenburg 2004) showing rapid recovery of endangered frogs after removal of introduced non-native fish (trout) from habitats, will help the frogs as they face new threats such as disease, drought and climate change (Written by Vance Vredenburg).
This species was featured as News of the Week on 11 February 2019:
A study by Ellison et al. (2019) investigates the interaction between Batrachochytrium dendrobatidis (Bd), the pathogen that causes the disease chytridiomycosis, and the bacterial skin microbiome of the endangered Sierra Nevada Yellow‐legged frog, Rana sierrae, using both culture‐dependent and culture‐independent methods. The study found that the skin microbiome of highly infected juvenile frogs is characterized by significantly reduced species richness and evenness, and by strikingly lower variation between individuals, compared to juveniles and adults with lower infection levels. In a culture‐dependent Bd inhibition assay, the bacterial metabolites we evaluated all inhibited the growth of Bd. Together, these results illustrate the disruptive effects of Bd infection on host skin microbial community structure and dynamics, and suggest possible avenues for the development of anti‐Bd probiotic treatments (Written by Vance Vredenburg).
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Vredenburg, V. T., Knapp, R. A., Tunstall, T. S., and Briggs, C. J. (2010). ''Dynamics of an emerging disease drive large-scale amphibian population extinctions.'' Proceedings of the National Academy of Sciences, 107(21), 9689-9694.
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Written by Vance Vredenburg (vancev AT sfsu.edu), San Francisco State University
First submitted 2007-04-02
Edited by Kellie Whittaker; updated by Ann T. Chang (2019-02-11)
Species Account Citation: AmphibiaWeb 2019 Rana sierrae: Sierra Nevada Yellow-legged Frog <http://amphibiaweb.org/species/6901> University of California, Berkeley, CA, USA. Accessed Oct 18, 2019.
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Citation: AmphibiaWeb. 2019. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 18 Oct 2019.
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