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Anurans of Costa Rica: Focus on the Golden Toad
Within a 22 year time period, the golden toad had been discovered, fascinating many people, including scientists, and then disappeared. This toad was discovered in 1967, the last one seen was in 1988, and was declared extinct in 1992. Scientists barely had any time at all to study this brilliant creature as it was the only known toad not to display the color grey or brown. Before its recent extinction, the golden toad had become the “poster frog” for Costa Rica’s endangered biodiversity. The golden toad vanished without a notice and people still wonder about it today.
I. Life History
The golden toad is a poorly known species and is assumed to share many characteristics and phylogenetic history with Bufo holdridgei since they live in the same habitat with intense conditions. The golden toad lived in a small area with elevation levels ranging between 2000-2100 m in the Monteverde Cloud Rainforest. This picky toad had a preferred habitat that occupied a wet, montane area in the forest. Judging by the size of the toad, it is assumed that they fed on small invertebrates that shared the same habitat.
The golden toad was an “explosive breeder” during heavy rain season for a few weeks in April gathering in small temporary bodies of water. The male competition was high and intense with a male-female ratio of 8:1. The males would get the females attention by a vibration signal that would also disengage the other males. “Males also exhibited a behavior known as ‘toad balls’ in which 4-10 males would clasp each other” (DeGroot 2000). A female would lay a string of 200-400 eggs that would remain in the temporary pool for the 5 week metamorphosis. The breeding period would be the only time that the secretive golden toad was seen. This gives scientists the hypothesis that they lived underground like its probable relative Bufo holdridgei. This colorful toad would be hard to miss if not underground for its striking orange coloration. “Discoverer, [Jay] Savage ‘confess[ed] that [his] initial response…was one of disbelief and suspicion that someone had dipped the examples in enamel paint’” (Sarkar and Sahotra 1996). Exhibiting strong sexual dimorphism, the females are black or yellow with red blotches edged in yellow and are significantly larger than the males in size. Again, it is hard to state their natural history since they were sighted only during the breeding season of 22 years. Most of their natural history is assumed from what is known about closely-related, sympatric toads.
II. Importance to the Ecosystem
Since there's so little known about Bufo periglenes, it's difficult to make any definitive statements about its position in an ecosystem. Furthermore, their range was so restricted; their importance in an ecosystem was probably negligible. They were once abundant in their very narrow habitat and probably consumed many small arthropods. Their contribution to upper trophic levels is unknown since observations of predation on them are very rare and almost completely unknown.
The anurans of Costa Rica are accountable for the striking species diversity. Species lost turns into a decrease of species diversity for the ecosystems of the rainforest. Species diversity is important in that it encourages evolutionary adaptation, ecological succession, competition, keeps populations healthy, creates more broad food webs, etc. “Amphibians are extremely sensitive indicators of environmental changes- uptake of oxygen and water through their skin can increase concentrations of pollutants, and the life cycle of frogs and toads exposes them to water and airborne contaminants” (Windeler 2005). Anurans are indicators of approaching environmental problems because of the extraordinary exposure to environmental factors and dissolved substances by their permeable skin, larvae and unshelled eggs, and greatly because of their life cycle involving both water and land. The disappearance of the golden toad is of particular significance since its habitat is in a national preserve.
III. Extinction Theories
There are various theories as to why the golden toad suddenly disappeared in the late 1980s. The theories include global warming, El NiĖo, the golden toad’s restricted range, climatic change, desiccation, a fungal disease called chytridiomycosis, airborne pollution, parasites, UV-B radiation, and lowered pH levels. Some experts believe that the toad’s extinction is due to a combination of these factors as some of these environmental issues are directly correlated. These frogs are considered to be a “reproductively vulnerable species” due to the narrow window of time and climatic preferences to breed.
There was a 1986-1987 El NiĖo which resulted in the lowest rainfall and highest temperatures on record. “Because of their dependence of water for breeding and their moist, permeable skins, anurans are unusually sensitive to moisture and temperature” (Sarkar and Sahotra 1996). It is believed that the low rainfall and high temperatures could have reduced the breeding ranges for the toad since their breeding pools were so small. A few days without rain could also result in desiccation of the developing eggs/tadpoles under metamorphosis that depend on water. Another hypothesis is that when temperature increases and moisture decreases, the contaminants in the air “reach critical concentrations” (Windeler 2005) and increases the susceptibility of disease to anurans. The habitat of the golden toad recurrently form clouds and mist which has declined dramatically since the mid 1970s due to the warming of the oceans and atmosphere (Kirby 1999).
The fungal disease called chytridiomycosis attacks the skin leading to eventual suffocation/dehydration. This is thought to affect the golden toad’s population because of their lowered immunity to the disease in the time that El NiĖo hit Costa Rica. It is also believed that the decreased moisture had decreased the golden toad’s habitat which increased crowding, and lead to the spread in disease.
Ultraviolet Radiation and Pollution
Large amounts of pesticides are used for agricultural uses in Costa Rica; including atrazine which is the most commonly used pesticide. Atrazine is known to have serious effects on the sexual development of anurans through airborne contact and evaporation. Ultimately, these environmentally sensitive toads rehydrated their dehydrated selves with highly toxic evaporative moisture when climatic changes occurred possibly from El NiĖo.
High levels of UV exposure is said to lower resistance to the common lake/pond fungus, Saprolegnia. UV levels were not so significant as to cause a whole population to plummet, but is considered an added stress to the golden toad population at that time.
Most of the theories on the extinction of the golden toad, such as El NiĖo, are natural causing which are beyond human control. There is still the possibility that the golden toad could still be alive, hiding out until conditions are right for reproduction. These types of mysteries are what make conservation biology so important today.
DeGroot, Jason. 2000. "Bufo periglenes” (On-Line), Animal Diversity Web.
Kirby, Alex. 1999. Climate Claims the Golden Toad.
Lips, Karen, Green, Earl, and Papendick, Rebecca. 2003. Chytridiomycosis in Wild
Frogs from Southern Costa Rica. Journal of Herpetology. 37: 215-218.
Perlman, David. 2006. Extinction Crisis for Amphibians: Frogs, toads and other species
Dying off—new fungus magnifies environmental problems. San Francisco
Sarkar, Sahotra. 1996. Ecological Theory and anuran declines. Bioscience. 46: 199-215.
Windeler, Britton. 2005. The Extinction of the Golden Toad (Bufo periglenes) –
Symptom of a Worldwide Crisis. http://jrscience.wcp.miamioh.edu/fieldcourses05/PapersCostaRicaArticles/TheExtinctionoftheGoldenT.html.
Young, Lips, Reaser, Ibanez, Salas, Ceneno, Coloma, Ron, Lamarca, Meyer, Munoz
Bolanos, Chavez, and Romo. 2001. Population Declines and priorities for
Amphibian conservation in Latin America. Conservation Biology. 15: 1213-1223.
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