| Mountain yellow-legged frog | |
|---|---|
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Amphibia |
| Order: | Anura |
| Family: | Ranidae |
| Genus: | Rana |
| Species: | R. muscosa |
| Binomial name | |
| Rana muscosa Camp, 1917 |
|
The Mountain yellow-legged frog (Rana muscosa) They prefer mountain creeks and lakes, particularly sunny riverbanks, meadow streams, isolated pools, and lake borders. They are generally found near steep gradient streams of a chaparral belt or other water sources around ≈1200–7550 feet.
Contents |
R. muscosa is a small (5–7.5 cm) frog species. Its lower abdomen and the underside of its hind legs are yellow or orange. It has a yellowish or reddish color on its dorsum, with black or brown spots or blotches. Juveniles have less color under their legs. When handled, it smells like garlic.
Male frogs of this species develop nuptial pads on their thumb base during the breeding season.
Once a thriving species, it was noticed in the 1970s that R. muscosa was absent from a significant part of its historic range. Over the course of the last one hundred years, 90 percent of Rana muscosa populations have vanished.[1] The remaining populations of R. muscosa are found in the southern Sierra Nevada of California, as well as the San Gabriel, San Bernardino, and San Jacinto Mountains in southern California.[2] The population at the San Bernardino Mountains had previously been considered extinct, though recently a small subset of the original population was found. As of right now, there are only six to eight populations in existence. These populations in some cases have less than 100 adults. In accordance with the IUCN Red List, R. muscosa is considered endangered.[2] R. muscosa’s decline is attributed to many other factors, including pesticide use, livestock grazing, drought, ultraviolet-B radiation,[3] and chytrid fungus.[4]
Recently for the first time in nearly 50 years, a population of the Mountain yellow-legged frog has been rediscovered in California's San Bernardino National Forest.[5]
R. muscosa’s aquatic habitat within high elevations of the Sierra Nevada was fish free 100 years ago. Trout were introduced to lakes and streams throughout the region in the late 1800s to increase recreational fishing in the area. However, tadpoles often become prey to non-native fish such as trout because this is a main source of food for this particular fish. At the tadpole stage, R. muscosa can take up to two years to mature,[2] and thus are vulnerable to fish predation for a long period of time.
Unfortunately, the introduced trout have caused a massive change in “the distribution of many native aquatic species.”[1] After R. muscosa was placed on the US Fish and Wildlife Service’s list as being “warranted” under the US Endangered Species Act it was suggested that removal of non-native fish, such as trout, might partially reverse R. muscosa’s dramatic population decline.[1] Thus, the removal of trout was driven into action.
Researchers Knapp et al. surveyed a group of lakes, including Black Giant, Cony, Lower LeConte, Marmot, No Good, and Upper LeConte to address the issue of non-native fish removal. Prior to the fish being removed, Black Giant, Cony, and No Good lakes all lacked R. muscosa. After the removal of fish at these lakes, R. muscosa once again was present.[1] It was difficult for researchers to calculate the total populations. The first evidence of reproduction was not expected until at least 2006. The first frogs detected at the sites where the non-native fish had been removed were small, young sub-adults. The transition from recently metamorphosed sub-adult to sexually mature adult can take up to four years in this species.[1] Removal of these non-native predatory fish has allowed for rapid increases in resident R. muscosa populations in some areas. Within the study area R. muscosa began to disperse to adjacent suitable aquatic habitats that previously contained fish or none at all.[6] Besides the effect of non-native fish on this species decline, there are also other sources, including pesticide use, climate change, and ultraviolet-B radiation.
Recent reports indicate a strong association between the disappearance of Rana muscosa from its historic aquatic habitats in California and wind-borne pesticides from agricultural land.[7][8] Pesticide use in the agricultural industry has been contributing to the loss of many species. Despite evidence that introduced fish and airborne pesticides might both be important factors impacting amphibian populations, no study has yet attempted to examine the role and relative importance of their effect on influencing amphibian populations. As a consequence, considerable debate continues over their respective roles in driving the decline of amphibians.[9]
Researchers Davidson and Knapp surveyed 6831 bodies of water and found that Rana muscosa was present at 13% and introduced fish were present at 16% of these aquatic locations.[9] Both fish and pesticides are a causative factor in the reduction of R. muscosa numbers. However, the presence of pesticides seems to have had a greater effect on these populations in comparison to other sources. However, at some lakes where fish were removed, the reintroduced frogs failed to survive. This was most likely due to upwind pesticide use. Recent research on the deceased frogs found at those sites indicated higher pesticide levels in their body tissue.[9] Pesticide use has led to other problems associated with amphibian health. Other researchers have shown that in the presence of pesticides, immune suppression is common, which makes amphibians more susceptible to disease. Pesticides are considered by some biologists an even greater threat to the overall population of R. muscosa than invasive trout.[10]
Environments are constantly changing due to destructive sources, like the non-native fish species and pesticide use. In accordance with agricultural or industrial developments nearby, studies found that carbaryl, a commonly used pesticide, directly infected aquatic environments from drift spraying or runoff. This particular chemical’s toxicity level increases with temperature[11] and ultraviolet-B radiation.[12] Studies have yet to make a direct connection to how much UV-B radiation and pesticides, in combination, will cause frog mortality. There are other sources causing the decline of Rana muscosa populations, but another, more persistent problem is a recently discovered fatal fungus.
A group of researchers, Longcore et al., discovered a new genus of chytrid fungus in 1999. This new fungus, known as Batrachochytrium dendrobatidis, became more widely studied because of its “disease-causing” factors in amphibians. This new fungus was considered to be fatal to frogs, leading to the disease called chytridiomycosis. B. dendrobatidis thrives in moist, cool environments[4] between wide ranges of temperatures, including 4 to 25 °C.[13] This fungus has the ability to grow within a wide range of temperatures, giving it many advantages. B. dendrobatidis has an optimum level of growth occurring between 17 and 25 °C. When it encounters temperatures around 4°C, the fungus becomes stunted, and reproduction is dramatically slowed. B. dendrobatidis then begins to “over winter” in its host until the temperature increases. Once temperatures rise, the fungus begins to multiply rapidly. B. dendrobatidis’ growth rate at temperatures lower than 10 °C is much slowed, but still maintainable. Studies showed that when some species of amphibians were placed in environments above 25 °C, B. dendrobatidis’ growth tapered off, deeming it non-harmful to its host and in some cases it appeared that the heat killed the fungus.[13]
Research has been aimed at trying to find out how this fungus is transmitted, how it impacts this species, and possible ways to prevent it from causing the total extinction of R. muscosa and many other species.[4] R. mucosa has experienced a great deal of mortality due to this infectious chytrid fungus. The majority of deaths of varied frog species infected with B. dendrobatidis occur during the subadult and adult phase. Highly keratinized locations on frogs are those first attacked by B. dendrobatidis. In tadpoles, only the jaw sheaths and tooth rows are affected; this constitutes a very small area of the body. A tadpole’s lack of keratinized areas on their body prevents the infection of B. dendrobatidis from causing them harm until they reach metamorphosis.[14] Adult, or “post-metamorphic”, frogs contain keratin all over their skin. This is why post-metamorphic frogs are more easily infected with B. dendrobatidis because there is more area to infect. To test for infections in tadpoles, the mouth parts are visually observed to see if a loss of pigmentation is evident. Evidence of the lack of pigmentation in the jaw sheaths, in tadpoles, is a strong indication of the presence of chytridiomycosis. However, there are problems associated with visually testing for this disease. The same depigmentation that is associated with chytridiomycosis is also seen in individuals during metamorphosis; but also those exposed to chemical contaminants and exposure to low temperatures.[4] A study performed on R. muscosa by Rachowicz and Vredenburg showed that there were differences in the appearance of the affected areas, mainly the jaw sheath in tadpoles. When exposed to low temperatures the appearance of the jaw sheath has continuous depigmentation, whereas infection of B. dendrobatidis has a gapped depigmentation appearance along the jaw sheath.[12]
This particular fungus affects frogs at different stages throughout its life.[4] Studies performed by Rachowicz and Vredenburg aimed to find out how readily B. dendrobatidis can be transmitted between different life stages of amphibians. One portion of this study was to see how easily frogs contract B. dendrobatidis when exposed to another frog that has been previously infected. Frogs studied were at tadpole and post-metamorphic life stages. The results showed that when R. muscosa was exposed for less than two weeks they did not contract the disease. However, when the post-metamorphic individuals were exposed beyond two weeks they appeared to have depigmentation in the jaw sheath, indicating infection. Another portion of this study was to see how easily it is to infect previously uninfected tadpoles. Transmission rates were present between uninfected and infected populations of tadpoles. When testing the effectiveness of the transmission, visual observation indicated signs of increased depigmentation at different times throughout the study. The jaw sheath showed to have lost all pigmentation in each individual, the time of visual infection ranged from week 7 to week 15 after inoculation of B. dendrobatidis.[12]
The ability of this new chytrid fungus to have such a strong hold on frog species may also be contributed to other environmental factors. These included climate change and the association of pesticide use with increased exposure to UV-B. All of these affect the immune system in the individual frogs.[15]
Climate change has had a large impact on amphibian environments. The increase in temperatures due to global warming has directly caused the hydrological cycle to become altered. This causes the timing of snow melt events to occur at different times than they normally did in the past. This can lead to droughts or even the complete “desiccation” of bodies of water in amphibian environments. This small increase in temperature can cause the life cycle of amphibians to be negatively affected along with the actual survival of offspring and the individual itself.[16]
In association with climate change, the ozone layer has been affected. The thinning of the ozone layer by multiple sources of pollution has created an entryway for a greater amount of ultraviolet-B radiation to reach the earth’s surface. Field and laboratory research has proved that there is a direct correlation between elevated levels of UV-B and amphibian sensitivity of eggs, embryos and larvae. This type of radiation causes the DNA to break apart resulting in abnormal development or death of the forming offspring.[17]
Interactions between ultraviolet-B radiation and other environmental factors can have an effect on frog populations. However, species have also developed their own way for coping with these types of environmental stressors. These coping mechanisms include behavioral avoidance, meaning that the individual seeks out a hiding spot, such as one formed by leaf litter or if able to swim to a deeper part of its aquatic environment. Other species will also go to such lengths to find a suitable place to deposit their eggs. A number of species try and find a place that has less exposure to UV-B. Some species have the ability to repair themselves from the effects of UV-B. Others have their own variation of protection from this type of radiation. This includes compounds that helps absorb this particular wavelength of light.[11] A conglomerate of different peptides exist in all amphibian species and some help prevent against the chytrid fungus. Some studies have been researched by Rollins-Smith et al. on antimicrobial peptides that Rana muscosa contains in its skin. Unfortunately, the study discovered that R. muscosa just happens to be more susceptible to B. dendrobatidis than other species in nature even with the help of its own antimicrobial peptides.[18]
There is evidence that proposes ultraviolet-B radiation has a negative influence in regards to a decrease rate in hatching success and an increase in embryonic death. Some problems associated with UV-B include deformities, changes in behavior, and a slowing of an individuals’ growth and developmental patterns.[12] The effects that UV-B has on different species varies in accordance with their sensitivity level. Plainly speaking, some species may be affected a little, while others may not be affected whatsoever.[11] Ultimately, more field studies need to be done in order to identify and classify which species are affected by UV-B. This will help to estimate the level that each species can tolerate before severe damage or mortality occurs to the individual frog species.
Predation from invasive fish species, such as the trout, has caused the Rana muscosa species to become stressed and is one of the many reasons for its past and current decline. Pesticide use has caused a decrease in amphibian immune suppression, making them more susceptible to disease. Along the line of climate change; ozone depletion, increased ultraviolet-B radiation and rises in temperature have all led to the endangered status of Rana muscosa. Due to immune suppression caused by pesticides and other factors, and the rising temperatures related to global warming, the chytrid fungus has played a major role in the rapid decline of Rana muscosa. It is for these reasons that there is an urgent need for more in depth studies. This will allow for an understanding of the loss of many amphibian species.
Anurans have unique characteristics that make them good bioindicators of pollution within their environment. This is due to the ability of their skin to be absorptive, allowing their bodies to soak up pollution within their environment. The down side is that most of the pollutants they absorb stay in their body, rather than exit back out into their habitats.[19] Various amounts of pesticides are continually entering the Earth’s water, soil, and air, creating a poisonous environment for many different species.
Pesticides are so widely used in our environment today that for many it is hard to believe that they are actually poisonous. Pesticides are defined by the California Department of Pesticide Regulation as any substance that controls, destroys, repels, or attracts a pest. Pesticides include insecticides, insect repellents, miticides, herbicides, fungicides, fumigants, nematicides, rodenticides, avicides, plant growth regulators, defoliants, desiccants, antimicrobials, and algicides.[20] These poisons we call pesticides, create residue that can be found today in every body of water on Earth. Nearly every animal species around the world, including humans and human breast milk (30) also contain forms of pesticide residues. Most pesticides are unfortunately not applied correctly; in California alone, it is estimated that only 0.01 to 5 percent of the 1. 7 billion pounds of reported pesticides used in 2007, reached their intended target.[20] The U.S. Environmental Protection Agency (EPA) estimates that in 2001, 4,972 million pounds of pesticides were used in the United States.[21]
One of the most commonly used pesticides in the United States is a broad leaf weed suppressant called Atrazine. In California, in 2000 alone, an estimated 55,284 pounds of Atrazine was used.[22] Atrazine is a Restricted Use Pesticide,[23] where both the U.S. EPA and the State of California restrict its use. RUP’s can be used only by applicators certified and licensed by the state, and only under specific conditions. This restriction is due to the acute toxicity RUP’s cause in humans and valuable insects. RUP’s may also cause illnesses, groundwater contamination, kill birds and fish, and even cause damage to other crops due to pesticide drift.[24] Atrazines’ known health effects according to the EPA include cancer, congestive heart failure, lung and kidney damage, low blood pressure, muscle degeneration and spasms, weight loss, retinal damage, damage to the adrenal glands, and disruption of the reproductive and developmental processes,[21] and yet the products that contain Atrazine are only required to have CAUTION on their labels.[25] Pesticides like Atrazine are not only affecting human life, but they are also taking a toll on amphibian life as well.
In areas where pesticides have not been used for more than twenty-five years, frogs have been found with pesticides in their bodies.[26] This may occur because pesticides such as Atrazine do not break down quickly in the environment.[27] Pesticides generally enter amphibian environments through agricultural runoff, which usually finds its way into breeding ponds in differing amounts throughout the year. In mid-to-late July, levels of Atrazine were between 0.1 and 6.7 ppb in these breeding ponds as reported to the USDA. When the weather changes and storms become more consistent, levels of Atrazine were as high as 480 ppb. The amount of Atrazine during this time had been measured in rainfall at levels upwards of 40 ppb.[26] There is a great deal of Atrazine in waterways that is having adverse affects on amphibians.
The problems associated with amphibian exposure to these chemical pollutants include effects on plasma thyroxine, plasma corticosterone, larval size, developmental stage, body condition, hermaphrodism and demasculinized larynges, and increased susceptibility to infection. Other side effects of exposure to Atrazine include “edema, erratic swimming and irregular behavioral activity”.[28] Exposure rates to Atrazine were tested by Tyrone Hayes. He showed that hermaphroditism occurred in larvae of both Rana pipiens and Xenopus laevis at levels as low as 0.1ppb. Previous studies on Atrazine have shown that this endocrine disruptor causes male amphibian larvae to be chemically castrated and feminized. Hermaphroditism in amphibians and mammals may result from androgen converting to estrogen.[26] Ultimately, the effects of Atrazine on the organism depend on the point of which it is exposed during its life cycle.[26]
The metamorphosis of frogs most commonly occurs in an aquatic environment and they generally come in to contact with more than one type of pesticide here. Multiple pesticides used on agricultural lands make their way into watersheds from runoff. Hayes et al. (2006) studied impacts of mixtures of nine pesticides in the wild and their effects in low concentrations, finding negative effects on amphibian development and growth. Based on these negative effects it was assumed that the survivorship of each species would also be affected, though it was not seen in this study.
One of the pesticides, propiconizole, caused levels of development to retard, in addition to delayed metamorphosis. Atrazine was seen to reduce the size of the individual at the time of metamorphosis. All nine pesticides were examined at 0.1 ppb, which is stated to be an “ecologically relevant concentration”.[19] Studies have addressed the issue of short term exposure to pesticides, but have yet to address how long term exposure may affect amphibians, as well as humans.
Atrazine is the most commonly used pesticide found in ground and surface water, as well as in soils.[27] Atrazine persists within soil from sixty to one hundred days because it is not readily absorbed by soil particles. This allows it to readily permeate ground water sources leading to contamination.[27] Pesticide drift causes the waterways and air to become contaminated. Exposure to chemical pollutants in the atmosphere has severely decreased air quality. Amphibians and humans alike are affected by pesticide drift. The amounts of pesticides in the air can cause simple problematic issues like asthma, or serious issues such as illness, birth defects, and cancer.[24] Studies have been performed in regards to the level of Atrazine and what is safe for human consumption. In accordance with the standards of water quality, there should be no more than 3 parts per billion (ppb) in drinking water.[21] The most commonly tested amount of Atrazine on amphibians is 0.1 ppb. This small amount has shown to cause malformations in some species of frogs. The “safe” amount of Atrazine in drinking water is thirty times greater than the amount that causes malformations in amphibians.[29] The EPA ignores the phenomena of "pesticide drift", the occurrence of pesticides being carried by wind. Gaseous pesticides such as fumigant pesticides and nearly every other pesticide used today moves easily through the air, and into communities where people live, work, and play.[24]
Around the world people are beginning to educate themselves and their communities of the growing dangers of pesticides in their environments. Atrazine is banned in France, Denmark, Germany, Norway, and Sweden.[24] Community-based green roots movements are growing to ban deadly pesticide use in their surrounding environment. Local organizations are lobbying to regulate the use of pesticides. Cases have been brought to the Supreme Court in Canada in regards to local rights to prohibit pesticide use in their communities.[24]
Many are concerned that regulation of pesticides is flawed, suffering from a lack of uniformity in the laws that regulate pesticide use that results from decentralized decision making by local and state governments.[24] The EPA, under the Federal Insecticide Fungicide and Rodenticide Act (FIFRA), makes the decisions regarding the regulation of pesticide use in the United States.[21]
Another serious fault in EPA’s registration process is the assumption that label instructions on pesticides are followed and enforced by the user. The same registration process that assures human health and the environment will remain protected is based on the theory that the instructions on the label will be followed. These instructions include applying the correct amount, and not applying the pesticide near water or during breezy conditions. Enforcement of the label restrictions is not overseen by the EPA, but is passed to the state or local regulatory systems.[24]
The EPA relies almost exclusively on studies conducted by the pesticide industry or its paid consultants.[24] These people are in favor of testing pesticides on people so as to eventually increase the allowable levels of exposure to humans and the environment.[24] This directly violates the congressional mandate under which the FIFRA had passed. Even though the EPA has shown the risks to workers, and surrounding communities, it rarely bans or imposes restrictions that adequately prevent harm to the environment of people from occurring.[24] The EPA’s inconsistent definition of "reasonable" risk varies. As an example the risk of cancer, can range from of one in a million to one in 10,000.[24] The EPA has continually ignored epidemiological studies of cancer risk when exposed to Atrazine and Captan, two of the most widely used pesticides in the US.[24]
In California, after realizing that children are more sensitive to pesticides in general and the health concerns regarding the side effects of many pesticides are likely to be life altering, action was taken to create the Integrated Pest Management (IPM) program.[20] The IPM regulates the use of pesticides around areas inhabited by children.[20] IPM was brought into effect with the understanding that pesticides may cause adverse health effects in humans such as cancer, neurological disruption, birth defects, genetic alteration, reproductive harm, immune system dysfunction, endocrine disruption, and acute poisoning. The IPM’s goal is to provide the safest, lowest risk approach to control pest problems while protecting people, the environment, and property. Regulatory practices, such as IPM, have become the standard for school districts and communities nationwide.[30]
New programs are continually being invented or adopted from other countries in order to reduce the amount of chemical pollutant exposure to all Earth’s creatures. Environmental activists claim even though there are less or non-toxic methods or products available to control pests and weeds, the EPA ignores these strategies because the current system assumes that if a pesticide meets an "acceptable" risk threshold, it has value or benefit.[24] Many studies have provided evidence that pesticides do in fact cause harm to amphibian species such as frogs and toads. For this reason alone, above all, is why more organics need to be used in order to replace the pollutants that are entering this environment.
There are a multitude of different products that can be substituted for pesticides. One of the current trends suggests using organic methods. This includes new farming methods, biological controls, and organic materials used to bring back soil fertility. The purpose of using organic materials is to repair degraded soil. This can be done by adding soil amendments that restore the quality of the soil. Poor quality soil can be due to inadequate surface soil aggregation, low porosity, and slow infiltration. All of these problems cause decreased crop yields and can lead to nonpoint source pollution from agricultural runoff to become amplified.[31]
Organic farming is a method that uses manures and compost to stabilize the levels of nitrogen in the soil.[31] This style of farming takes into account what type of soil nutrients are needed for specific crops to grow. The fertility of soil is tested to determine which nutrients are missing so as to not over fertilize particular crops. Together they help to manage nutrients in the soil, making it more fertile.[32] Some studies have shown that using organic instead of synthetic fertilizers improved all attributes of the soil as well as the crop yields. The use of compost helps to reduce “mineralization rates” which decrease the “potential for nitrate” to leach.[31] By using these organic materials to help mend the soil, they will also help to prevent pollution from entering waterways and poisoning amphibian life.
Other methods deal with planting techniques and include the use of biological defenses to help maintain and sustain crops. By understanding the different components of soil, such as pH, nutrients, and water retention, one can plant the correct crop and get the most output.[33] Intercropping and crop rotation are two techniques that can be used to boost soil fertility.[32] Intercropping enables multiple crops to be planted on the same plot of land. It has many benefits, including reduction of pest populations, plant diseases, and erosion.[33] Crop rotation plans for the specific crops to be planted one growing season after another. Each crop planted helps the following crop by maintaining soil nutrient levels. This practice has numerous benefits including the prevention of soil depletion. Other benefits include the reduction of soil erosion, as well as a decreased reliance on synthetic pesticides and fewer pests. In addition to these benefits there is also weed control and disease prevention.[33] Biological defenses can be used as well. This includes using ladybugs to get rid of aphids and praying mantises to get rid of other small insects. Collectively, the use of organic fertilizers, composting, and crop planting methods all help to minimize the use of chemical pesticides, thereby helping to sustain Anurans and other wildlife.
Data related to Rana muscosa at Wikispecies