User:Arinna.guo/Sierra Nevada yellow-legged frog

The Sierra Nevada yellow-legged frog or Sierra Nevada Mountain yellow-legged frog (Rana sierrae) is a true frog endemic to the Sierra Nevada of California and Nevada in the United States. It was formerly considered Rana muscosa until a 2007 study elevated the more central and northern populations to full species status, restricting R. muscosa to the southern Sierra Nevada and southern California. The frog is listed as an Endangered species for protection under the Federal Endangered Species Act.

Once abundant in the Sierra Nevadas, the ecological effects of their loss have been significant as they were a keystone species and important for nutrient and energy cycling in the aquatic and terrestrial ecosystems.

Description

The Sierra Nevada yellow-legged frog is one of the two mountain yellow-legged frog species which include Rana sierrae and Rana muscosa. The Sierra Nevada yellow-legged frog (Rana sierrae) is very similar in appearance to the southern mountain yellow-legged frog (Rana muscosa), with which it was formerly identified. The two were separated into different species after there were observed differences in mitochondrial DNA. This species of frog is considered to be aquatic and is found within close proximity to water usually within a few meters. The frogs appear either yellow or brown and have both brown and black spots. The belly of the frogs is more noticeably yellow and can also appear orange. Tadpoles of this species appear black or brown and take between one to four years to fully develop. On average, they grow up to 3.5 inches long and females tend to be larger than males.

Sierra Nevada yellow legged frogs can also be grey, red, or greenish-brown with dark splotches. These splotches look like lichen or moss, making the frogs camouflaged; this type of coloration is cryptic coloration. The belly and the underside of the back legs are yellow, giving rise to the name.

If disturbed, these frogs can produce a garlic-like odor to ward off threats like predators.

Habitat and Range

These frogs inhabit mountain bodies of water such as streams, lakes, wetlands, and flooded meadows from 4,500m to 12,000m. They spend most of their lives in or around these water sources as they provide essential food sources and raising ground for tadpoles. The frogs inhabit both the East and Western Sierras down to areas North of Lake Tahoe. Although their range has not changed, the population density of the species has declined over the years due to their endangered status as well as other threats to their habitat.

Adults can be found sitting on large rocks of the shoreline where there is little vegetation whole larvae are distributed in warm shallow areas of water during daytime

Breeding sites include ponds, lakes, and streams that do not dry out, are deep enough to prevent freezing, and are without fish.

Endemic Range of the Sierra Nevada yellow-legged frog.

Food Sources

Sierra Nevada yellow-legged frogs eat a variety of terrestrial and aquatic invertebrates and even tadpoles. It has also been found that they will consume their own eggs.

Adults preferentially feed on terrestrial insects and adult stages of aquatic insects in shallow ares of water. Larvae eat algae and diatoms of stream beds.

Frogs tend to hunt by waiting until they see prey come into range and then strike. They may also creep up on prey and then strike. They use their sticky tongues to catch their prey and bring it into their mouths.

Life Cycle

Breeding for this species starts in spring which varies on the elevation of the area between April and July. Eggs are left in groups underwater with an average size of 233 eggs and are attached to something in the water. The eggs will then hatch between 18 and 21 days. The tadpoles which hatch from the eggs will then develop into adult frogs over a period ranging from 1 to 4 years. The frogs will then reproduce, therefore, repeating the cycle.

Oviposition occurs is shallow waters of ponds. Egg masses are can be attached ricks, gravel, vegetation, or under banks.

Conservation status

The Sierra Nevada yellow-legged frog has been declared endangered by the IUCN and was last assessed in 2008. Studies showed that 92.5% of the species populations have gone extinct. These declines have been caused in most part by disease and invasive predators. Shallow lakes that dry in summer endanger this high-elevation frog. Predation by non-native trout also plays a large role in limiting breeding and tadpole development. The trout eat many of the tadpoles that are produced while also competing against adult frogs for resources. Areas containing trout have seen major declines in the frog population and experiments have shown that the removal of the trout leads to a rise in the frog population. Many factors endangering the southern mountain yellow-legged frog also affect this species. A disease called chytridiomycosis has led to the extinction of entire populations of the species. This disease is caused by Batrachochytrium dendrobatidis or bd. Populations that have been infected by the disease have either been eradicated or reduced to a few individuals.

Studies show that a recently discovered amphibian chytrid fungus is contributing to the decline of the Sierra yellow-legged frog. Chytrid fungus leads to Chytridiomycosis, a disease than can be fatal. Chytrid fungus lives on keratin which is found on the external mouthparts of tad poles and the outer skin later of adults. The growth of this fungus on adults disrupts the species ability to breathe through its skin and osmoregulate. More research on the origins and spread of chytrid fungus is still need.

Conservation Strategies

Yosemite

In 2006, Yosemite National Park began a Yosemite Conservancy supported protect to introduce frogs into lakes without fish. In 2007, a project was started to restore frog habitat by removing non-native fish from remote sites. Once the site is fishless, lakes are inhabited by native species, including the Sierra Nevada yellow-legged frog.