The Golden Toad of Monteverde, Costa Rica was among the first casualties of amphibian declines. Formerly abundant, it was last seen in 1989.

Dramatic declines in amphibian populations, including population crashes and mass localized extinction, have been noted since the 1980s from locations all over the world. These declines are perceived as one of the most critical threats to global biodiversity, and several of causes are believed to be involved, including habitat destruction and modification, over-exploitation, pollution, pesticide use, introduced species, climate change, increased ultraviolet-B radiation (UV-B) and disease. However, many of the causes of amphibian declines are still poorly understood, and the topic is currently a topic of much ongoing research. Download high resolution version (3593x2400, 1410 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (3593x2400, 1410 KB) Wikipedia does not have an article with this exact name. ... Binomial name Bufo periglenes Savage, 1967 The Golden Toad or Monte Verde Toad (Bufo periglenes) lived in handfulls of places in the Monteverde forest located in Costa Rica, a country in Central America. ... For other uses, see Monteverde (disambiguation). ... Year 1989 (MCMLXXXIX) was a common year starting on Sunday (link displays 1989 Gregorian calendar). ... For other uses, see Extinction (disambiguation). ... The 1980s refers to the years from 1980 to 1989. ... Rainforests are among the most biodiverse ecosystems on earth Biodiversity is the variation of taxonomic life forms within a given ecosystem, biome or for the entire Earth. ... Habitat destruction is a process of land use change in which one habitat-type is removed and replaced with some other habitat-type. ... It has been suggested that Pollutant be merged into this article or section. ... A cropduster spreading pesticide. ... Sweet clover (), introduced and naturalized to the U.S. from Eurasia as a forage and cover crop. ... Variations in CO2, temperature and dust from the Vostok ice core over the last 450,000 years For current global climate change, see Global warming. ... UV redirects here. ... This article is about the medical term. ...

Background

In the past three decades, declines in populations of amphibians (the group of organisms that includes frogs, toads, salamanders, newts, and caecilians) have occurred worldwide. In 2004, an international convention of amphibian biologists announced that 32 percent of species are currently threatened, 43 percent were declining in population,^[1] and that 120 species are likely to have become extinct since the 1980s.^[2] Genera See text. ... Genera Ansonia Atelopus Bufo Capensibufo Crepidophryne Dendrophryniscus Didynamipus Frostius Laurentophryne Leptophryne Melanophryniscus Mertensophryne Nectophryne Nectophrynoides Nimbaphrynoides Oreophrynella Osornophryne Pedostibes Pelophryne Peltophryne Pseudobufo Rhamphophryne Werneria Wolterstorffina The true toads are amphibians in the Bufonidae family. ... Families Salamander is the common name applied to approximately 500 amphibian vertebrates with slender bodies, short legs, and long tails (order Caudata or Urodela). ... smooth newt Newts are small, usually bright-coloured semiaquatic salamanders of North America, Europe and North Asia. ... See also: Caecilian, bishop of Carthage, 312 C.E. Families Rhinatrematidae Ichthyophiidae Uraeotyphlidae Scolecomorphidae Caeciliidae The Caecilians are an order (Gymnophiona or Apoda) of amphibians which resemble worms or snakes. ...

Declines have been particularly intense in the western United States, Central America, South America, eastern Australia and Fiji (although cases of amphibian extinctions have appeared worldwide). While human activities are causing a loss of much of the world’s biodiversity, amphibians appear to be suffering much greater effects than other species of organisms. Because amphibians generally have a two-staged life cycle consisting of both aquatic (larvae) and terrestrial (adult) phases, they are sensitive to both terrestrial and aquatic environmental effects. Because their skins are highly permeable, they may be more susceptible to toxins in the environment than other organisms such as birds or mammals.^[3] Many scientists believe that amphibians serve as "canaries in a coal mine," and that declines in amphibian populations and species indicate that other groups of animals and plants will soon be at risk.^[3] For other uses, see Central America (disambiguation). ... South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ... Animal environments are classified as either aquatic (water), terrestrial (land), or amphibious (water and land). ... Larvae are the plural of larva, juvenile form of animals with indirect development. ... Terrestrial animals are animals that live predominantly or entirely on land, as compared with aquatic animals, which live predominantly or entirely in the water (e. ... For the adult insect stage, see Imago. ... An estuary mouth and coastal waters, part of an aquatic ecosystem. ... For a list of biologically injurious substances, including toxins and other materials, as well as their effects, see poison. ...

Declines in amphibian populations were first widely recognized in the late 1980s, when a large gathering of herpetologists reported noticing declines in populations in amphibians across the globe.^[4] Among these species, the Golden toad of Monteverde, Costa Rica featured prominently. The Golden Toad, Bufo periglenes, was the subject of scientific investigation until populations suddenly crashed in 1987 and disappeared completely by 1989.^[5] Other species at Monteverde, including the Monteverde Harlequin Frog (Atelopus varius), also disappeared at the same time. Because these species were located in the pristine Monteverde Cloud Forest Reserve, and these extinctions could not be related to local human activities, they raised particular concern among biologists. Herpetology (Greek herpeton = to creep, to ramp and logos = in this context explanation or reason) is the branch of zoology concerned with the study of reptiles and amphibians. ... Binomial name Bufo periglenes Savage, 1967 The Golden Toad or Monte Verde Toad (Bufo periglenes) lived in handfulls of places in the Monteverde forest located in Costa Rica, a country in Central America. ... For other uses, see Monteverde (disambiguation). ...

Initial skepticism

When amphibian declines were first presented as a conservation issue in the late 1980s, some scientists remained unconvinced of the reality and gravity of the conservation issue.^[6] Some biologists argued that populations of most organisms, amphibians included, naturally vary through time. They argued that the lack of long-term data on amphibian populations made it difficult to determine whether the anecdotal declines reported by biologists were worth the (often limited) time and money of conservation efforts.

However, since this initial skepticism, biologists have come to a consensus that declines in amphibian populations are a real and severe threat to biodiversity.^[2] This consensus emerged with an increase in the number of studies that monitored amphibian populations, direct observation of mass mortality in pristine sites that lacked apparent cause, and an awareness that declines in amphibian populations are truly global in nature.^[7]

Potential causes

Numerous potential explanations for amphibian declines have been proposed. Most or all of these causes have been associated with some population declines, so each cause is likely to affect in certain circumstances but not others. Many of the causes of amphibian declines are well-understood, and appear to affect other groups of organisms as well as amphibians. These causes include habitat modification and fragmentation, introduced predators or competitors, introduced species, pollution, pesticide use, or over-harvesting. However, many amphibian declines or extinctions have occurred in pristine habitats where the above effects are not likely to occur. The causes of these declines are complex, but many can be attributed to emerging diseases, climate change, increased ultraviolet-B radiation, or long-distance transmission of chemical contaminants by wind.

Habitat modification

Main article: Habitat destruction

Habitat modification or destruction is one of the most dramatic issues affecting amphibian species worldwide. As amphibians generally need aquatic and terrestrial habitats to survive, threats to either habitat can affect populations. Hence, amphibians may be more vulnerable to habitat modification than organisms that only require one habitat type. Habitat destruction is a process of land use change in which one habitat-type is removed and replaced with some other habitat-type. ...

Habitat fragmentation

Main article: Habitat fragmentation

Habitat fragmentation occurs when habitats are isolated by habitat modification, such as when a small area of forest is completely surrounded by agricultural fields. Small populations that survive within such fragments are often susceptible to inbreeding, genetic drift, or extinction due to small fluctuations in the environment. Habitat fragmentation is a process of environmental change important in evolution and conservation biology. ... It has been suggested that inbreeding depression be merged into this article or section. ... In population genetics, genetic drift is the statistical effect that results from the influence that chance has on the success of alleles (variants of a gene). ...

Introduced species

Main article: Introduced species

Non-native predators and competitors have also been found to affect the viability of frogs in their habitats. The mountain yellow-legged frog which typically inhabits the Sierra Nevada lakes have seen a decline in numbers due to stocking of non-native fish (trout) for recreational fishing. The developing tadpoles and froglets fall prey to the fish in large numbers. This interference in the frog's three year metamorphosis is causing a decline that is manifest throughout their ecosystem.^[8] Sweet clover (), introduced and naturalized to the U.S. from Eurasia as a forage and cover crop. ... Binomial name Rana muscosa The Mountain yellow-legged frog (Rana muscosa) is a small (5-7. ... This article is about the mountain range in the Western United States. ... Rainbow trout, Oncorhynchus mykiss Biwa trout (or Biwa salmon), Oncorhynchus masou rhodurus Trout is the common name given to a number of species of freshwater fish belonging to the salmon family, Salmonidae. ... Fishing is the activity of hunting for fish by hooking, trapping, or gathering. ... A Pieris rapae larva An older Pieris rapae larva A Pieris rapae pupa A Pieris rapae adult Metamorphosis is a process in biology by which an individual physically develops after birth or hatching, and involves significant change in form as well as growth and differentiation. ...

Chemical contaminants

There is clear evidence that chemical pollutants are causing frog developmental deformities (extra limbs, or malformed eyes). Pollutants have varying effects on frogs. Some alter the central nervous system; others like atrazine cause a disruption in the production and secretion of hormones. Experimental studies have also shown that exposure to commonly used herbicides such as glyphosate (Tradename Roundup) or insecticides such as malathion or carbaryl greatly increase mortality of tadpoles.^[9] Additional studies have indicated that terrestrial adult stages of amphibians are also susceptible to non-active ingredients in Roundup, particularly POEA, which is a surfactant.^[10] Atrazine has been shown to cause male tadpoles of African clawed frogs to become hermaphroditic with development of both male and female organs. Such feminization has been reported in many parts of the world.^[11] In a study conducted in a laboratory at Uppsala University in Sweden, more than 50% of frogs exposed to levels of estrogen-like pollutants existing in natural bodies of water in Europe and the United States became females. Tadpoles exposed even to the weakest concentration of estrogen were twice as likely to become females while almost all of the control group given the heaviest dose became female.^[12] Many of the compounds which are dangerous to the environment can also be harmful to humans in the long-term range and come from mineral and fossil sources or are produced by humans themselves. ... A diagram showing the CNS: 1. ... Atrazine, 2-chloro-4-(ethylamine)-6-(isopropylamine)-s-triazine, is an s-triazine-ring herbicide that is used globally to stop pre- and post-emergence broadleaf and grassy weeds in major crops. ... It has been suggested that Roundup be merged into this article or section. ... Roundup is the brand name of a systemic, broad-spectrum herbicide produced by the U.S. life sciences giant Monsanto. ... Malathion is a organophosphate parasympathomimetic which binds irreversibly to cholinesterase. ... Carbaryl is a chemical in the carbamate family used chiefly as an insecticide. ... Surfactants, also known as tensides, are wetting agents that lower the surface tension of a liquid, allowing easier spreading, and lower the interfacial tension between two liquids. ...

A study published in the September 24, 2007 issue of Proceedings of the National Academy of Sciences shows that high levels of nutrients used in farming and ranching activities fuel parasite infections that have caused frog deformities in ponds and lakes across North America. The study showed increased levels of nitrogen and phosphorus cause sharp hikes in the abundance of trematodes, and that the parasites subsequently form cysts in the developing limbs of tadpoles causing missing limbs, extra limbs and other severe malformations.^[1] According to Pieter Johnson, an ecologist and evolutionary biologist at the University of Colorado at Boulder who led the study, "You can get five or six extra limbs. You can get no hind limbs. You can get all kinds of really bizarre, sick and twisted stuff." ^[13] is the 267th day of the year (268th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st Century. ... The Proceedings of the National Academy of Sciences of the United States of America, usually referred to as PNAS, is the official journal of the United States National Academy of Sciences. ... The University of Colorado at Boulder (CU-Boulder, UCB officially[3]; Colorado and CU colloquially) is the flagship university of the University of Colorado System in Boulder, Colorado. ...

While most pesticide effects are likely to be local and restricted to areas near agriculture, there is evidence from the Sierra Nevada mountains of the western United States that pesticides are traveling long distances into pristine areas, including Yosemite National Park in California. This article is about the mountain range in the Western United States. ... Yosemite National Park (pronounced Yo-SEM-it-ee, IPA: ) is a national park located largely in Mariposa and Tuolumne Counties, California, United States. ... Official language(s) English Capital Sacramento Largest city Los Angeles Largest metro area Greater Los Angeles Area  Ranked 3rd  - Total 158,302 sq mi (410,000 km²)  - Width 250 miles (400 km)  - Length 770 miles (1,240 km)  - % water 4. ...

Some recent evidence points to ozone as a possible contributing factor to the worldwide decline of amphibian.^[14] It has been suggested that Ozone generator be merged into this article or section. ...

Disease

A number of diseases have been related to mass die-offs or declines in populations of amphibians, including "red-leg" disease (Aeromonas hydrophila), Ranavirus (Family: Iridiviridae), Anuraperkinsus, and chytridiomycosis. It is not entirely clear why diseases have suddenly begun to affect amphibian populations, but some evidence suggests^[15] that these diseases may have been spread by humans, or may be more virulent when combined with other environmental factors. Binomial name Aeromonas hydrophila (Chester, 1901) Stanier, 1943 Aeromonas hydrophila is a heterotrophic, gram-negative bacterium, mainly found in areas where the climate is really warm. ... Chytridiomycosis in Atelopus varius - two sporangia containing numerous zoospores are visible Chytridiomycosis is a fatal infectious disease that affects amphibians, caused by the chytrid - Batrachochytrium dendrobatidis . ...

Trematodes

There is considerable evidence that parasitic trematode platyhelminths (a type of fluke) have contributed to developmental abnormalities and population declines of amphibians in some regions.^[16] These trematodes of the genus Ribeiroia have a complex life cycle with three host species. The first host includes a number of species of aquatic snails. The early larval stages of the trematodes then are transmitted into aquatic tadpoles, where the metacercariae (larvae) encyst in developing limb buds. These encysted life stages produce developmental abnormalities in post-metamorphic frogs, including additional or missing limbs.^[4] These abnormalities increase frog predation by aquatic birds, the final host of the trematode. Subclasses Aspidogastrea Digenea The Trematoda is a class within the phylum Platyhelminthes, which contains two groups of parasitic worms. ... Ribeiroia is a genus of parasite in the class Trematoda, phylum Platyhelminthes. ...

Chytridiomycosis

Main article: Chytridiomycosis

In 1998, following large-scale frog deaths in Australia and Central America, research teams in both areas came up with identical results: a previously undescribed species of pathogenic fungus, Batrachochytrium dendrobatidis. It is now clear that many recent extinctions of amphibians in Australia and the Americas are linked to this fungus. This fungus belongs to a family of saprobes known as chytrids that are not generally pathogenic. Chytridiomycosis in Atelopus varius - two sporangia containing numerous zoospores are visible Chytridiomycosis is a fatal infectious disease that affects amphibians, caused by the chytrid - Batrachochytrium dendrobatidis . ... A pathogen (literally birth of pain from the Greek παθογένεια) is a biological agent that can cause disease to its host. ... Batrachochytrium dendrobatidis is a recently discovered chytrid fungus that causes the amphibian disease chytridiomycosis. ... Orders Chytridiales Spizellomycetales Monoblepharidales Blastocladiales Neocallimasticales Chytridiomycota is a division of the Fungi kingdom and contains only one class, Chytridiomycetes. ...

The disease caused by Batrachochytrium dendrobatidis is called chytridiomycosis. Frogs infected by this disease generally show skin lesions and hyperkeratosis, and it is believed that death occurs because the fungus makes it impossible for the amphibian to respire across the skin. The time from infection to death has been found to be 1–2 weeks in experimental tests.

Subsequent research has established that the fungus has been present in Australia since at least 1978, and present in North America since at least the 1970s. The first known record of chytrid infection in frogs is in the African Clawed Frog, Xenopus laevis. Because Xenopus are sold in pet stores and used in laboratories around the world, it is possible that the chytrid fungus may have been exported from Africa. Binomial name Xenopus laevis Daudin, 1802 The African clawed frog (Xenopus laevis, also known as platanna) is a species of South African aquatic frog of the genus Xenopus. ...

Climate change

Main article: Climate change

Large stands of ecosystem such as rainforests are being destroyed at a phenomenal rate decreasing available habitat. Also pollutants indirectly affect frogs by way of ozone depletion causing sun burn damage to the delicate moist skins of frogs, and further affecting their immune systems. Variations in CO2, temperature and dust from the Vostok ice core over the last 450,000 years For current global climate change, see Global warming. ... A coral reef near the Hawaiian islands is an example of a complex marine ecosystem. ... The Daintree Rainforest in Queensland, Australia. ... Global monthly average total ozone amount Ozone depletion describes two distinct, but related observations: a slow, steady decline of about 4 percent per decade in the total amount of ozone in Earths stratosphere since around 1980; and a much larger, but seasonal, decrease in stratospheric ozone over Earths... A scanning electron microscope image of a single neutrophil (yellow), engulfing anthrax bacteria (orange). ...

Increased ultraviolet-B radiation

Like many other organisms, increasing ultraviolet-B (UVB) radiation due to stratospheric ozone depletion and other factors may harm amphibians. The amount of damage depends upon the life stage, the species and other environmental parameters. Thus, for some species, UVB may harm early stages such as egg or larval stages whereas for other species it may be harmful to adult stages (e.g. eye damage). Exposure to UVB radiation may not kill a particular species or life stage but may cause sublethal damage. UVB radiation may act synergistically with climate change, contaminants and diseases. However, these speculations are not supported by experimental evidence.

Recent reviews of published studies done to test effects of UVB on amphibians showed that most studies found significant mortality on embryos and increases in deformities when exposed to natural levels of UVB. This emphasizes the fact that UVB radiation is important to consider in amphibian population declines.

Over millions of years, amphibians have evolved inefficient protection against damage from UVB when faced with the recent unprecedented levels of UVB reaching the earth's surface due to human-induced destruction of the earth's protective ozone layer. More than three dozen species of amphibians have been studied with severe effects reported in more than 40 publications in peer-reviewed journals representing authors from North America, Europe and Australia.

Increased noise levels

Frogs and toads are highly vocal, and their reproductive behaviour often involves the use of vocalizations. There have been suggestions that increased noise levels caused by human activities may be contributing to their declines. In a study in Thailand, increased ambient noise levels were shown to decrease calling in some species and to cause an increase in others. This has, however, not been shown to be a cause for the widespread decline. ^[17]

Amphibian Ark project

Such is the seriousness of the case, on February 16th 2007, scientists worldwide met in Atlanta, US to form a group called the Amphibian Ark to save more than 6,000 species of amphibians including frogs, salamanders and wormlike caecilians from disappearing due to the Chytridiomycosis fungus and other issues affecting the amphibian population.^[18] Amphibian Ark (or AArk) coordinates captive breeding programs for threatened amphibians species, implemented by partners around the world. ... Families Rhinatrematidae Ichthyophiidae Uraeotyphlidae Scolecomorphidae Typhlonectidae Caeciliidae The Caecilians are an order (Gymnophiona or Apoda) of amphibians which resemble earthworms or snakes. ... Chytridiomycosis in Atelopus varius - two sporangia containing numerous zoospores are visible Chytridiomycosis is a fatal infectious disease that affects amphibians, caused by the chytrid - Batrachochytrium dendrobatidis . ...

References

19. McCallum, M.L. 2007. Amphibian decline or extinction? Current declines dwarf background rates. Journal of Herpetology 41: 483-491. is the 261st day of the year (262nd in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st Century. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st Century. ... is the 60th day of the year (61st in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st Century. ... is the 53rd day of the year in the Gregorian calendar. ...

External links

• FrogWeb: Amphibian Declines & Malformations
• Global Amphibian Assessment which reviews the current status of amphibian species worldwide
• AmphibiaWeb provides background information on amphibian declines.
• Reptile Amphibian & Pesticide (RAP) Database
• Weedicide induced feminization
• Herpetological Conservation and Biology Journal dedicated to herp conservation