The mountain yellow-legged frog (''Rana muscosa''), also known as the southern mountain yellow-legged frog, is a species of

true frog True frogs is the common name for the frog family Ranidae. They have the widest distribution of any frog family. They are abundant throughout most of the world, occurring on all continents except Antarctica. The true frogs are present in North Am ...

endemic to California in the United States. It occurs in the

San Jacinto Mountains The San Jacinto Mountains (''Avii Hanupach''Munro, P., et al. ''A Mojave Dictionary''. Los Angeles: UCLA. 1992. in Mojave) are a mountain range in Riverside County, located east of Los Angeles in southern California in the United States. The mo ...

San Bernardino Mountains The San Bernardino Mountains are a high and rugged mountain range in Southern California in the United States. Situated north and northeast of San Bernardino and spanning two California counties, the range tops out at at San Gorgonio Mountain ...

, and

San Gabriel Mountains The San Gabriel Mountains ( es, Sierra de San Gabriel) are a mountain range located in northern Los Angeles County and western San Bernardino County, California, United States. The mountain range is part of the Transverse Ranges and lies betw ...

Southern California Southern California (commonly shortened to SoCal) is a geographic and cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most populous urban ...

and the Southern

Sierra Nevada The Sierra Nevada () is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primar ...

. It is a federally listed

endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inv ...

.Mountain yellow-legged frog (''Rana muscosa'')
United States Fish and Wildlife Service. Populations formerly classified as ''Rana muscosa'' in the northern Sierra Nevada have since been redescribed as a new species: '' Rana sierrae'', the Sierra Nevada yellow-legged frog. The Sierra Nevada yellow-legged frog has also been classified as an endangered species since 2013. The mountains separating the headwaters of the South Fork and Middle Fork of the Kings River mark the boundary between the ranges of the two species.

Description

''Rana muscosa'' is 4 to 8.9 centimeters long. Females tend to be larger than males. Its color and patterning are variable. It is yellowish, brownish, or olive with black and brown markings. The underside of its hind legs can be different hues of yellow, from a bold sun yellow to a lighter pale yellow; larger ones may can hints of orange on their hind legs. The throats of it range from white to yellow.United States Department of Agriculture (2014)
“MOUNTAIN YELLOW-LEGGED FROG CONSERVATION ASSESSMENT for the SIERRA NEVADA MOUNTAINS OF CALIFORNIA, USA.
/ref> Along with its variable coloration, the frog also has a dorsal pattern with dark spots in different shapes and sizes. Its species name ''muscosa'' is from the

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

meaning "mossy" or "full of

moss Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta ('' sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and ...

", inspired by its coloration. It may have light orange or yellow thighs. When handled, the frog emits a defensive odor reminiscent of garlic.''Rana muscosa'' - Southern Mountain Yellow-legged Frog
California Herps: A Guide to the Amphibians and Reptiles of California. 2013.

Habitat

The frog occurs in mountain creeks, lakes and lakeshores, streams, and pools, preferring sunny areas. It rarely strays far from water, and can remain underwater for a very long time, likely through cutaneous gas exchange. As such, adults can be found on rocks around shorelines. Close proximity to water is important because eggs are either laid underwater attached to rocks or in shallow waters. The

tadpole A tadpole is the larval stage in the biological life cycle of an amphibian. Most tadpoles are fully aquatic, though some species of amphibians have tadpoles that are terrestrial. Tadpoles have some fish-like features that may not be found ...

s require a permanent water habitat for at least two years while they develop. This is because tadpoles can die from a lack of moisture, especially dry summers. The frog has been noted at elevations of between about 1,214 and 7,546 feet (370 and 2,300 meters) in Southern California. These habitats are primarily found in north of California in Sierra Nevada and south of California in the Transverse ranges.

Reproduction and Early Life

The frog emerges from its wintering site soon after snowmelt. Its breeding season begins once the highest meltwater flow is over, around March through May in the southern part of its range, and up to July in higher mountains to the north. Fertilization is external, and the egg cluster is secured to vegetation in a current, or in still waters sometimes left floating free. How long it takes for breeding onset varies from 1-4 years depending on the levels of snow and temperature. Very cold temperatures may cause death of larvae. The juvenile may be a tadpole for 3 to 4 years before undergoing

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...

. However, this rate heavily varies depending on the temperature and elevation of the area. There are two classes of tadpoles: first year tadpoles and second year tadpoles. Metamorphosis tends to happen the second summer of tadpole life. They are called metamorphs when this transition from tadpole to young frog is occurring. They are then called a juvenile when it survives one winter. It becomes ready to reproduce after 2 years of the juvenile stage. It is found that the growth and development rate is slower at higher elevations.

Behavior

The frog lacks a

vocal sac The vocal sac is the flexible membrane of skin possessed by most male frogs and toads. The purpose of the vocal sac is usually as an amplification of their mating or advertisement call. The presence or development of the vocal sac is one way ...

. Its call is raspy, rising at the end. During the day, it calls underwater. The frogs tend to be less active during the winters and more active during the mating season. For years when there is heavy snow at high elevations, they may only be active for 90 days in the summer. Hibernation tends to happen underwater or in the crevices of stream banks. This occurs during the cold months of winter. Hibernation ends in the spring to start the breeding season. This species feeds on aquatic insects and benthic invertebrates. Their diet varies depending on the habitat type. When living in streams, it tends to eat terrestrial insects such as beetles, ants, bees, wasps, flies, and dragonflies. They are also known to eat larvae of other frogs and toads, as well as commit cannibalism.

Decline

Once a common species, ''Rana muscosa'' was absent from much of its native range by the 1970s. Over the course of the last hundred years, 90% of its populations have been eliminated.Knapp, R. A., et al. (2007)
"Removal of nonnative fish results in population expansion of a declining amphibian (mountain yellow-legged frog, ''Rana muscosa'')'
''Biological Conservation'' 135(1):11-20. The frog was known from 166 locations in the Southern California mountains, and as of 2007, only seven or eight remained. The 2009 discovery of ''R. muscosa'' at two locations in the

San Bernardino National Forest The San Bernardino National Forest is a United States National Forest in Southern California encompassing of which are federal. The forest is made up of two main divisions, the eastern portion of the San Gabriel Mountains and the San Bernard ...

was newsworthy.Nearly extinct California frog rediscovered.
NBC News. July 24, 2009. The frog is represented in the Sierra Nevada by three or four populations. Its decline is attributed to many factors, including

introduced species An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived there ...

of fish such as trout, livestock grazing,Vredenburg, V
The Mountain Yellow-legged Frog - Can They be Saved?
''Sierra Nature Notes'' Volume 1. January, 2001.

chytrid fungus Chytridiomycota are a division of zoosporic organisms in the kingdom Fungi, informally known as chytrids. The name is derived from the Ancient Greek ('), meaning "little pot", describing the structure containing unreleased zoöspores. Chytrid ...

,The Amphibian Chytrid Fungus and Chytridiomycosis.
Amphibianark.org. Retrieved 04 August 2013. and probably pesticides, drought, and ultraviolet radiation. Recreational activities in streams have also had an impact.

Introduced fish species

Trout were introduced to lakes and streams throughout the Sierra Nevada in the late 1800s to increase

recreational fishing Recreational fishing, also called sport fishing or game fishing, is fishing for leisure, exercise or competition. It can be contrasted with commercial fishing, which is professional fishing for profit; or subsistence fishing, which is fishing fo ...

in the area. 90% of these Sierra Nevada lakes and streams did not previously have fish in them, although the trout were regionally present. The fish feed on tadpoles, a main prey item. The fish feed on tadpoles, a main prey item. Some of these fish types that prey on tadpoles include the brown, golden, and rainbow trout, as well as the brook char. The introduced trout have changed the distribution of several native species in the local ecosystems. Most of the mountain yellow-legged frog populations did not evolve to adapt to the trout. The trout caused populations to isolate, restricted the amount of available habitats, and increased the chances of extinction. After the removal of fish from several lakes, the frog reappeared and its populations increased. These frogs then began to disperse to other suitable habitats nearby.

Pesticides

The decline of the frog from its historic range has been associated with pesticide drift from agricultural areas. Frogs that have been reintroduced to water bodies cleared of fish have failed to survive, and analysis has isolated pesticides in their tissues. Pesticides are considered by some authorities to be a greater threat to the frog than the trout. The relative roles that pesticides and introduced fish play in frog declines are still debated, and the loss of ''R. muscosa'' in its former range has probably been influenced by multiple factors.

Chytridiomycosis

This species is one of many amphibians affected by the fungal disease

chytridiomycosis Chytridiomycosis ( ) is an infectious disease in amphibians, caused by the chytrid fungi '' Batrachochytrium dendrobatidis'' and '' Batrachochytrium salamandrivorans''. Chytridiomycosis has been linked to dramatic population declines or extinc ...

. Ample research has explored the biology of the fungus and how to prevent related amphibian declines. The fungus attacks

keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up Scale (anatomy), scales, hair, Nail ...

ized areas of a frog's body. Tadpoles are not severely affected because only their jaw sheaths and tooth rows are heavily keratinized. Infection in a tadpole can be identified by changes in the pigmentation of these parts. Adults have keratin-rich skin and suffer worse infections. In studies, healthy adult frogs exposed to infected frogs for at least two weeks developed the disease. Transmission takes longer in tadpoles, generally over seven weeks. Frogs may be predisposed to infection if their immune systems are weakened by other factors, such as pesticide. Studies indicate that ''R. muscosa'' is naturally more susceptible to the chytrid fungus than many other frogs.

Conservation Status and Efforts

The frog is an endangered species under the US

Endangered Species Act The Endangered Species Act of 1973 (ESA or "The Act"; 16 U.S.C. § 1531 et seq.) is the primary law in the United States for protecting imperiled species. Designed to protect critically imperiled species from extinction as a "consequence of ec ...

. The

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

has also listed it as endangered. Its NatureServe conservation status is Imperiled.''Rana muscosa''
NatureServe. 2012. The first successful

captive breeding Captive breeding, also known as captive propagation, is the process of plants or animals in controlled environments, such as wildlife reserves, zoos, botanic gardens, and other conservation facilities. It is sometimes employed to help species tha ...

of the frog occurred in 2009 when three tadpoles were reared at the

San Diego Zoo The San Diego Zoo is a zoo in Balboa Park, San Diego, California, housing 4000 animals of more than 650 species and subspecies on of Balboa Park leased from the City of San Diego. Its parent organization, San Diego Zoo Wildlife Alliance, is a p ...

. Conservation workers at the zoo plan to release any more surviving captive-bred frogs in the

, part of their native range.Mountain Yellow-legged Frog Hopping for Survival.
San Diego Zoo Global. The first successful

of the frog occurred in 2009 when three tadpoles were reared at the

. Conservation workers at the zoo plan to release any more surviving captive-bred frogs in the

, part of their native range.Mountain Yellow-legged Frog Hopping for Survival.
San Diego Zoo Global. In 2015 frogs and tadpoles of the species were reintroduced to Fuller Mill Creek in the

and

.SoCal Wild.com: "Building a Mountain Frogtown for Yellow-Legged Frogs"
Brenda Rees, editor; 10 August 2015. They were bred and raised the Arnold and Mabel Beckman Center for Conservation Research in Escondido, one of the organizations that have partnered with the San Diego Zoo Institute for Conservation Research (ICR) to save the species from extinction. The Los Angeles Zoo is also a coalition partner and is raising two groups of wild collected tadpoles from two localities in the

where they are released when ready. In 2015, the

Oakland Zoo The Oakland Zoo is a zoo located in the Grass Valley neighborhood of Oakland, California, United States. Established on June 6, 1922, it is managed by the Conservation Society of California, a 501(c)(3) non-profit organization dedicated to the ...

began a rehabilitation project of the frog in order to fuel efforts to save the species. Every year, a group of tadpoles are taken from native lakes throughout California and brought to the zoo. There, the tadpoles are grown to juvenile frogs, while also undergoing an inoculation process to render them immune to the

fungus disease. Once ready, the now chytrid immune juvenile frogs are released back into the lakes they were found. In 2016, the Oakland Zoo released 53 specimens into various lakes in Sequoia and Kings Canyon National Parks. The program is set to release 130 inoculated individuals into lakes in Sequoia and Kings Canyon National Parks and

Inyo National Forest Inyo National Forest is a United States National Forest covering parts of the eastern Sierra Nevada of California and the White Mountains of California and Nevada. The forest hosts several superlatives, including Mount Whitney, the highest po ...

in 2017. In 2021, the

Aquarium of the Pacific The Aquarium of the Pacific (formerly the Long Beach Aquarium of the Pacific) is a public aquarium on a site on Rainbow Harbor in Long Beach, California, United States. It is situated across the water from the Long Beach Convention Center, Shor ...

partnered with government organizations like the

California Department of Fish and Wildlife The California Department of Fish and Wildlife (CDFW), formerly known as the California Department of Fish and Game (CDFG), is a state agency under the California Natural Resources Agency. The Department of Fish and Wildlife manages and protec ...

to create a facility for taking care of mountain yellow-legged frogs. This was in response to recent wildfires which harmed their habitats. Following the wildfires, wildlife agencies found and moved these frogs into places like the facility established by the Aquarium of the Pacific. These efforts help the species recover from natural disasters and prevent extinction.

References

External links

*Fisher, R. N. and T. J. Case. (2003)

A Field Guide to the Reptiles and Amphibians of Coastal Southern California. USGS.
The Mountain Yellow-legged Frog Site.

''Rana muscosa''
AmphibiaWeb.
''Rana muscosa'' vocalizations
Western Soundscape Archive.
Mountain Yellow Legged Frog Release
{{DEFAULTSORT:Mountain Yellow-Legged Frog Rana (genus) Amphibians of the United States Endemic fauna of California Fauna of the Sierra Nevada (United States) Natural history of the Peninsular Ranges Natural history of the Transverse Ranges Endangered fauna of California ESA endangered species Amphibians described in 1917