| Foothill yellow-legged frog | |
|---|---|
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Amphibia |
| Order: | Anura |
| Family: | Ranidae |
| Genus: | Rana |
| Species: | R. boylii |
| Binomial name | |
| Rana boylii Baird, 1854 |
|
The Foothill Yellow-legged Frog (Rana boylii) is a small-sized (3.72-8.2 cm) frog[2] from the Rana genus in the Ranidae family. This species can be found from northern Oregon, down California’s west coast, and into Baja California, Mexico. Both the Columbia Spotted Frog and the Cascades Frog, also part of the Rana genus, live in the northern regions of this frog's territory. They prefer to live in streams and rivers, and lay their eggs in masses attached to rocks underwater.
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The Foothill Yellow-legged Frog has a grey, brown, or reddish dorsum, or the back of the frog. It is commonly spotted or mottled but occasionally is plainly colored. Adults have yellow coloration under the legs, which may extend to their abdomen, but this characteristic is faint or absent in young frogs. There is a triangular, buff-colored patch on the snout, and, unlike other frogs in the Rana genus, there is no eye stripe. The throat and chest are often boldly mottled; moreover, the species has indistinct dorso-lateral skin folds and granular skin. Males of this species develop a nuptial pad on their thumb base during the breeding season. These frogs can be identified by their rough skin, horizontal pupils, fully webbed hind feet, and its habit to jump into moving water.[3] However, tadpoles of this species resemble that of their rival, the Western Toad or Bufo boreas. The R. boylii as tadpoles have fairly flattened tails that lack color at the end and are the tallest in the mid section. The mouth of the tadpoles are made for suction to rocks with lip, known as labial, teeth rows used for scraping algae and diatoms, unicellular algae with cells walls that contain silica, off of the rocks they are clinging to. The mouth of the young R. boylii is also helpful in identifying it from B. boreas because the young Foothill Yellow-Legged frogs develop more defined teeth rows after three weeks while their counterparts do not.[3]
Food supplies such as algae that the tadpoles eat also affects the sexual maturity of the species. It has been reported that the “amount of protein in different algae, can affect size at and time to metamorphosis” and that “these food effects may be mediated through diet induced changes in thyroid function,” which means that the food that the tadpoles ingest dictates the changes in the thyroid gland's production of certain proteins.[4] Tadpoles most commonly feed on algae, diatoms, and detritus. As the species grows older, it changes its diet to animal tissue which must be swallowed whole because the frog's jaw is structured on a hinge joint that does not allow for sideways movement as in humans. Adult frogs eat a range of foods such as moths, ants, grasshoppers, hornets, beetles, flies, water striders, and snails.[5]
The mating “ceremonies” begin in spring where adult frogs congregate on sandy and/or rocky bars to mate. It was previously believed that they did so from March to May, but recent experiments have determined that time to be closer to April to late June[3]. High stream velocities, however, may dislodge R. boylii egg masses from oviposition substrates.[6] Thus, R. boylii avoids rapid waters to protect the egg masses from being swept away. This technique is why the species has a wide window for breeding season. If the conditions are not perfect to their standards, they will refuse to mate and will wait until the water velocities go back down to ideal.
For the Foothill Yellow-Legged Frog, the oviposition, or the depositing of eggs, is somewhat sporadic because delays such as rains could cause problems like unwanted removal of eggs.[3] The males also perform mating calls mostly underwater, and those above the water are faint and hard to hear over fifty meters. After the frogs have successfully mated, the egg masses are ovipositioned about half a meter down in the river and with flow velocities ranging from 0.1 to 0.6 m3/second.[6] These egg masses can be anywhere from 100 to 1000 eggs in one batch. They are contained in a bluish gel that disappears once the eggs take on water, and the dark ovum, center of egg, is covered by three jelly envelopes that are about 5.4 mm in diameter. Eggs hatch in about five to over thirty days depending on the temperature that the mass is at and the surrounding water.[3] The tadpoles continue to stay associated with the egg mass for several days, and continue to need higher temperatures to grow quickly. By the time the tadpoles reach about forty millimeters, roughly 1 and a half inches, they are adults and their reproductive organs are mostly functional. The frogs are usually fully developed by the summer after their first metamorphosis, though some begin breeding after six months.
The Foothill Yellow-Legged Frog has a territory that spans from northern Oregon, down California's coast where it most commonly found, and into Baja California, Mexico. They prefer to be in streams and rivers versus still ponds and perfer flowing water that has either rocky substrate or sunny banks and rivers and streams that contain shallow areas that still have water flow.[5]
R. boylii has a chemical defense in which it can protect itself from fungal infections, such as the Batrachochytrium dendrobatidis.[7] The frog secretes a peptide through the skin and the hydrophobic (water repellent) sections of the peptide access to fungi that want to attach to the amphibian.[8] This ability can also be found in other Rana species including the Cascades Frog and the Moor Frog. The former secretes a milky substance that fights against fungal infections and the latter uses its capability to have males turn blue during mating season. Still, the Foothill Yellow-Legged Frog's chemical defense has not been fully examined and is in the process of being understood. Although not much is known about it, this ability of the species has been of interest to many anti-fungal cream companies because of its overall effectiveness. However, current pesticide use has caused problems for the frog. So far, it has been concluded that though exposure to carbaryl, a substance found in common pesticides, does not kill the frogs, it does lower the peptides’ abilities to defend the species against invaders like the chytrid, B. dendrobatidis.[7] More research is being done to see the full effects that pesticides may have on R. boylii.
Along with the problems associated with pesticides being washed up in the Foothill Yellow-Legged Frog's habitat, in Trinity County, California there is a dam on the major river of the frog's home which has affected about 94% of the possible procreation areas for the frogs, which has endangered the population.[3] One study suggests that the “data from a comparably-sized undammed river fork in the same system…demonstrated that both the number of potential sites and the total number of egg masses were…higher on this fork than in our main stem,” and so the unseasonal flooding required by the dam was negatively affecting the mating behavior of the frog.[9] The temperature of the water in Trinity County is also lower than it was before the dam was put into place. To keep up with demands of fisheries, the water’s temperature is kept artificially lower than normal, which consequently slows the development of R. boylii.[9] Therefore, the colder temperatures are making it more difficult for the frogs to grow quickly, which sometimes leaves the species prey to many other animals that dine on their young. The problems occurring between the Foothill Yellow-Legged Frog and the dam are being handled by several herpetological organizations, along with the Forest Service, to find ways to alter the effects in a beneficial way for the frog. This species is also estimated to be gone from most of its range in the Sierra Nevada mountains, espcially south of highway 80 where pesticides often contaminate rivers and dams block the essential stream flows.[10]
The foothill yellow-legged frog is a natural prey of diving beetles, water bugs, garter snakes, rough-skinned newts, bullfrogs, and Western toads.[3]