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Golden toad

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| name = Golden Toad | image = Bufo periglenes2.jpg | image_caption = Male golden toad | status = EX | extinct = 1989 | status_system = iucn3.1 | status_ref = [1] | fossil_range = | regnum = Animalia | phylum = Chordata | classis = Amphibia | ordo = Anura | familia = Bufonidae | genus = Bufo | species = †B. periglenes | binomial = Bufo periglenes | binomial_authority = Savage, 1966 | range_map = | range_map_width = | range_map_caption = | synonyms = Cranopsis periglenes
Ollotis periglenes
Incilius periglenes }}

The golden toad (Bufo periglenes) was a small, shiny, bright true toad that was once abundant in a small region of high-altitude cloud-covered tropical forests, about 10 square kilometres (3.9 sq mi) in area, north of the city of Monteverde, Costa Rica. For this reason, it is sometimes also called The Golden Toad of Monteverde (Cranopsis periglenes) or the Monte Verde toad and is commonly known as the "poster child" for the Amphibian decline crisis.[2] Other common English names include Alajuela toad and orange toad. They were first described in 1966 by the herpetologist Jay Savage.[3] On 15 May 1989, a single male was found, and not a single B. periglenes is reported to have been seen anywhere in the world since, and it is classified by the International Union for Conservation of Nature (IUCN) as an extinct species.[1] Its sudden extinction might have been caused by chytrid fungus and extensive habitat loss.

Description

The golden toad was one of more than 500 species in the family Bufonidae—the "true toads". B. periglenes inhabited northern Costa Rica’s Monteverde Cloud Forest Reserve, distributed over an area of roughly 10 square kilometres (3.9 sq mi) at an average elevation of 1,500 metres (4,900 ft).[4] In the geographic ranges that the toads lived in, the areas tend to decrease in size with increasing elevation. So the higher up you travel on mountain tops and other areas with high geographic range, the less likely you were to find a golden toad.[5]

"Amphibian" is a Greek construction meaning "double life"-a reference to the fact that the typical amphibian life cycle is partly aquatic and partly terrestrial. At some 350 million years of age, Amphibia is the world's oldest terrestrial vertebrate class and there are more amphibians than there are mammals.[6] Amphibians' collective domain includes every continent except Antarctica, and probably most of the world's major islands. They achieve their greatest variety in tropical and warm temperate forests, but they also live in deserts, grasslands and northern bogs.[6]

Morphology

Adult males measured just barely 5 centimetres (2.0 in) long. Males have been described as being "Day-Glo golden orange",[7] and unlike most toads their skin was shiny and bright. Jay Savage was so surprised upon first seeing them that he did not believe they could be real; he is quoted as saying: "I must confess that my initial response when I saw them was one of disbelief and suspicion that someone had dipped the examples in enamel paint."[8] Exhibiting sexual dimorphism, female toads were slightly larger than the males, and looked very different. Instead of being bright orange, females were colored dark olive to black with scarlet spots encircled by yellow.

Reproduction

The Golden toad's main habitat was on one cold, wet ridges called Brillante, where it would emerge in the spring time for five to ten days at a time to mate in rainwater that pooled against the roots of the trees.[6] The most recent documented breeding episode occurred from April–May 1987, before the species became extinct.[9]

The toad is known for its particular breeding habits, known as gastric breeding. Once the male and the female toad creates a fertilized egg, the female swallows the eggs and keeps them in her stomach until they become young. For about a six-week span, the golden toad turns off its digestive system and it does not eat until the young toad offspring comes forth from the female toad’s mouth. Here, the young tadpoles go through their early stages of life in the comfortable and safe environment of their own mother’s stomach. Each toad couple produces a massive amount of eggs; the pairs have been known to produce anywhere from 200-400 eggs each week for the six week period, each with a diameter of about 3 mm. The remaining larva stays in the pool for about five weeks until it reaches a level of maturity where it can leave the pool.[10]

For a few weeks in April, after the dry season ended and the forest became wetter, males would gather in large numbers near ground puddles and wait for the females. The males would fight with each other for opportunities to mate until the end of their short mating season, after which the toads retreated to their burrows.[11] The most recent documented breeding episode occurred from April–May 1987, before the species became extinct.[9] For a few weeks in April, after the dry season ended and the forest became wetter, males would gather in large numbers near ground puddles and wait for the females. The males would fight with each other for opportunities to mate until the end of their short mating season, after which the toads retreated to their burrows.[11]

Males outnumbered females, in some years by as much as ten to one, a situation that often led bachelors to attack amplectant pairs and form what Savage once described as "writhing masses of toad balls". The eggs of the golden toad, black and tan spheres, were deposited in small pools—puddles—often no more than one inch deep. Tadpoles emerged in a matter of days, but required another four or five weeks for metamorphosis. During this period, they were highly dependent on the weather; too much rain and they would be washed down the steep hillsides, too little and their puddles would dry up. Golden toads were always found at an altitude of between 1490m and 1700m.

SK Jacobson and JJ Vandenberg conducted a study in 1991 in the Cordillera de Tilaran, Costa Rica. They discovered that golden toads bred explosively when it rained heavily from March to June. During the 1977 and 1982 seasons, males outnumbered females by over 8 to 1 at breeding pools. Single males attacked pairs twice as often as they attacked individual males, but no males were displaced. Male body size was not linked with mating success but size assortative mating occurred in 1977, according to Jacobson and Vandenberg. Life history characteristics like clutch size and large egg size were similar to other tropical montane toads. Yearly breeding activity was observed in B. periglenes since at least 1977 until cessation during 1988-1990. Their limited distribution and slow rate to reach maturity exacerbated their recent population decline.

The golden toad, like most frog species, is very dependent on water for breeding. Their porous, permeable skin makes them very sensitive to moisture and temperature. Thus, when 1987 hit, known as the “dry year” the frogs had a very difficult time breeding due to the climate changes the region was experiencing.[9] The increase in the temperature caused the mist frequency in the ecology of the highland forests of Monteverde to decline. The decline began to dramatically change in the mid-1970s because of the warming of the oceans and the atmosphere. The cloud formations in Costa Rica began to form at higher altitudes than before and researchers believe that changes of this sort lead to disease outbreaks.[12] The air could only become saturated and create mist through the cooling of the air to its dew point temperature or evaporating moisture into the air and increasing the water vapor content. [13] This did not occur because of the great increase in temperature of the surrounding environments.The dew point temperature is the temperature at which a parcel of air must be cooled at constant pressure and humidity mixing ratio until it reaches saturation and at which condensation of water vapor forms either as dew, cloud droplets, ice crystals, mist, or fog. In the case of the golden toads, the mist levels decreased, so with the warmer air more water vapor is retained and there is less mist where the golden toads can continue with their reproduction process. [14] In addition, El Niño and the Southern Oscillation left behind warm breeding pools which led to unsuitable conditions for reproduction, as well as heavy rainfall and a high pH balance in the water, all which disturbed the toads’ breeding patterns. After the storm hit, many breeding pools dried up and thousands of eggs and tadpoles were subsequently left to die.[10]

In 1987, an American ecologist and herpetologist, Martha Crump, was fortunate enough to see the toad's mating rituals. In her book, In Search of the Golden Frog [sic], she described it as "one of the most incredible sights I've ever seen", and said they looked like "statues, dazzling jewels on the forest floor".[7] On April 15, 1987, Crump recorded in her field diary that she counted 133 toads mating in one "kitchen sink-sized pool"[7] that she was observing. Five days later, she witnessed the pools in the area drying, which she attributed to the effects of El Niño-Southern Oscillation, "leaving behind desiccated eggs already covered in mold".[7] The toads attempted to mate again that May. Of the 43,500 eggs that Crump found, only twenty-nine tadpoles survived the drying of the forest's ground.[7]

Conservation history

The Monteverde Cloud Forest Preserve, the golden toad's previous habitat

Jay Savage first discovered the toads in 1966.[3] From their discovery in 1966 for about 17 years, and from April to July in 1987, over 1500 adult toads were seen.[4] Only ten[1] or eleven toads were seen in 1988,[4] including one seen by Crump, and none has been seen since May 15, 1989, when Crump last saw the same solitary male toad that she had seen the year before.[11]

In the period between discovery and disappearance, the golden toad was commonly featured on posters promoting the biodiversity of Costa Rica.[15] There is a single anecdotal report from the 1970s of a golden toad in the mountains of Guatemala near the village of Chichicastenango,[citation needed] but this sighting has not been confirmed. Holdridge's Toad, which was declared extinct in 2008 but has since been rediscovered, lives in the same forest in Costa Rica.

Extinction

See also: Gastric-brooding frog and Extinction risk from global warming

In the spring of 1987, an American biologist who had come to the cloud forest specifically to study the toads counted fifteen hundred of them in temporary breeding pools. That spring was unusually warm and dry and most of the pools evaporated before the tadpoles in them had time to mature. The following year, only one male was seen at what previously had been the major breeding site. Seven males and two females were seen at a second site a few miles away. The year after, on May 15, 1989, the last sighting of only one male occurred.[16] No golden toad has been seen since then. The Global Amphibian Assessment (GAA) lists 427 species as “critically endangered”, including 122 species that are “possibly extinct”. A majority of the former, and nearly all of the latter, have declined even in seemingly undisturbed environments.[5] As late as 1994, five years after the last sighting, researchers still hoped that B. periglenes continued to live in underground burrows, as similar toad species have lifespans of up to twelve years.[4] By 2004 IUCN listed the species as extinct, after an evaluation involving Savage (who had first discovered them 38 years earlier). IUCN's extinction was based on the lack of sightings since 1989 and the "extensive search[ing]" that had been done since without result.[1] In August 2010 a search organised by the Amphibian Specialist Group of the International Union for Conservation of Nature set out to look for various species of frogs thought to be extinct in the wild, including the golden toad.[17] In Costa Rica’s Monteverde cloud forest, frequency of mist in warm years and the fungi is associated with the disappearance of the golden toad. Cloudiness favours the chytrids which grows best at 17 to 25°C, peaking at 23° Celsius. They stop growing at 28°C and die at 30°C. These temperatures Shield from excessive warmth and welcome moist conditions, This chytrid grows on amphibian skin and produces aquatic zoospores, If amphibians seek warmth to combat the infection, increasing cloudiness might hamper their defences. In any case, local or microscale cooling should often benefit the chytrids.[5]

Jennifer Neville has examined the different hypotheses explaining the extinction of the golden toad in her article "The Case of the Golden Toad: Weather Patterns Lead to Decline". Neville comes to the conclusion that Crump's El Niño hypothesis is "clearly support[ed]" by the available data.[4] IUCN gives numerous possible reasons in its description of the past threats to the species, including "[the golden toad's] restricted range, global warming, chytridiomycosis and airborne pollution".[1] Neville also mentions arguments that an increase in UV-B radiation, fungus or parasites, or lowered pH levels contributed to the Golden Toad's extirpation.[4] However, Crump et al. (1992) concluded that conditions after 1987 were warmer than in 1987 after studying the temperatures of the golden toad breeding pools. “ Crump et al. (1992) based their conclusion on low pool temperatures recorded during the early-April cold front in 1987, when air temperatures briefly departed from the general pattern of positive anomalies.”.[5] J. Alan Pounds and Martha L. Crump’s data proves that 1987 conditions were in fact warmer than conditions after 1987 using Anomalies of daytime air temperatures at Monteverde.[10]

In 1991, ML Crump, FR Hensley and KL Clark attempted to understand whether the decline of the golden toad in Costa Rica meant that the species was underground or extinct. They found that each year from the early 1970s -1987 golden toads emerged from retreats to breed during April–June. During the time of the study in 1991, the most recent known breeding episode occurred during April/May 1987. Over1500 adults were observed at five breeding pools, but a maximum of 29 tadpoles metamorphosed from these sites. During April–June 1988-90, Crump et. al. found only 11 toads during surveys of the breeding habitat. To study the species' decline, they analyzed rainfall, water temperature, and pH of the breeding pools. The data on weather patterns and characteristics of the breeding habitat unveiled that warmer water temperatures and less precipitation during dry season after1987 could have caused adverse breeding conditions. The toads may have actually been alive and hiding in retreats, waiting for appropriate weather conditions. The scarcity of toads could have been a normal population response to an unpredictable environment.[18]

A more recent study supports the El Niño hypothesis (El Niño is the warm oceanic phase in the Eastern Pacific along with high air surface pressure in the Western Pacific that periodically occurs. It is said to cause climate change)[10] in conjunction with the chytrid fungus, stating that "...Monteverde was the driest it's been in a hundred years following the 1986–1987 El Niño, but that those dry conditions were still within the range of normal climate variability". The new study has shown that the chytrid fungus has spread due to the dry conditions caused by El Niño.[19] An estimated 67% of the 110 or so species of amphibians, endemic to the American tropics, have become extinct or endangered, and a pathogenic chytrid fungus (Batrachochytrium dendrobatidis) is implicated.[5]

Three hypotheses of how the chytrid fungus, Batrachochytrium dendrobatidis (Bd) could have caused the Golden Toad to go extinct is presented in the study "Evaluating the links between climate, disease spread, and amphibian declines" by Jason R. Rohr et al. They include the spatiotemporal-spread hypothesis, the climate-linked-epidemic hypothesis, and the chytrid-thermal-optimum hypothesis. The chytrid-thermal-optimum hypothesis proposes that global warming increased cloud cover in warm years resulting in the concurrence of daytime cooling and nighttime warming, temperatures that are the optimal thermal temperature for Bd growth.[20]

Kevin J. Anchukaitis and Michael N. Evans, authors of “Tropical cloud forest climate variability and the demise of the Monteverde golden toad”, also proposed the chytrid thermal optimum hypothesis. They presented the earlier study by Pounds and Crump based on the El Niño event in 1986-1987. After observing the dry conditions from higher temperatures and lower seasonal rainfall, they concluded that this could potentially be the cause for the Monteverde Golden Toad extinction. From there Chytridiomycosis caused by Bd was eventually identified as a major cause of the amphbian extinction throughout the world.[21]

To test it, they used Radiocarbon and Chronology Validation to test the amount of δ18O or (delta-O-18) which is commonly used as a measure of the temperature of precipitation. They found “El Niño Southern Oscillation (ENSO) years in the δ18O chronology show a isotopic cycle enrichment 0.8‰ (greater than 1σ) above the with a strong mean positive anomaly of 2.0‰ for 1983, 1987, and 1998 alone (greater than 2σ above the mean). These years of discernible strong positive anomalies in the monthly δ18O chronology correspond to periods of dry season drought.”[21]

In conjunction with the chytrid-thermal-optimum hypothesis, the climate-linked-epidemic hypothesis also suggests the correlation between climate change and the amphibian pathogen. Unlike the chytrid-thermal-optimum hypothesis, the climate-linked-epidemic hypothesis does not assume a direct chain of events between warmer weather and disease outbreak. In "Widespread amphibian extinctions from epidemic disease driven by global warming" J. Alan Pounds et al. established that global climate change is a direct link to species extinctions. Taking the results and recent findings that tie to the Golden Toad's population crash due to disease, Pounds concluded that climate-driven epidemics are an immediate threat to biodiversity. It also points to a chain of events whereby this warming may accelerate disease development by translating into local or microscale temperature shifts—increases and decreases—favourable to Bd.[5] There is then the case of the "climate-chytrid" paradox. Chytridiomycosis, caused by Batrachochytrium, grows on amphibian skin and produces aquatic zoospores. The chytrid becomes increasingly malignant under cold and moist conditions. Hence, the idea that the pathogen spreads in warmer climates is paradoxical. It is possible that the warmer climate made the species more susceptible to disease, or that warm years could have favored Batrachochytrium directly.[5]

In contrast to both chytrid-thermal-optimum hypothesis and the climate-linked-epidemic hypothesis, the spatiotemporal-spread hypothesis suggests that population declining due to Bd is caused by the introduction and spread of Bd from a finite amount of introduction sites instead of a link between Bd and climate change. They used a Mantel tests of all the possible hot spots Bd could have came from to see if their hypothesis was correct. They did see positive correlations between spatial distance and distance in timing of declass and the lat year observed. "Coincident mass extirpation of neotropical amphibians with the emergence of the infectious fungal pathogen Batrachochytrium dendrobatidis" by Tina L. Cheng et al., also parallels with the spatiotemporal-spread hypothesis by tracking the origins of Bd and tracking it from Mexico to Costa Rica.[22]

However, the last three collected and preserved specimens of the C. periglenes species and oddly enough were found negative for B. dendrobatidis. It is possible that either the testing methods weren't robust enough to detect the nascent infection, or that the specimens were too damaged to be tested. The more likely explanation is that the specimens were collected prior to the presumptive emergence and documentation of Bd in Monteverde. It is very likely that Bd played a role in the extinction of The Golden Toad, but there still isn't enough data to conclusively tie the pathogen with the now extinct species.[2]

See also

References

<div class="reflist reflist-columns references-column-width " style="column-width: 30e</ref></ref>m;">

  1. ^ a b c d e Template:IUCN
  2. ^ a b Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1670/11-243, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1670/11-243 instead.
  3. ^ a b Jay Savage (1966). "An extraordinary new toad from Costa Rica". Revista de Biología Tropical. 14: 153–167.
  4. ^ a b c d e f Jennifer J. Neville (2003). "The Case of the Golden Toad: Weather Patterns Lead to Decline". North Ohio Association of Herpetologists. Archived from the original on October 10, 2004. Retrieved July 27, 2006. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  5. ^ a b c d e f g Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1038/nature04246, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1038/nature04246 instead.
  6. ^ a b c Mattoon, Ashley (July/August 2000). "Amphibia fading". World Watch. 13 (4): 12–23. {{cite journal}}: Check date values in: |date= (help)
  7. ^ a b c d e Crump, Marty. In Search of the Golden Frog [sic] (1998) quoted in Flannery.
  8. ^ Savage, Jay quoted in Jennifer J. Neville (2003). "The Case of the Golden Toad: Weather Patterns Lead to Decline". North Ohio Association of Herpetologists. Archived from the original on October 10, 2004. Retrieved July 27, 2006. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  9. ^ a b c Sarkar, Sahotra (March 1996). "Ecological Theory and Anuran Declines". Bioscience: 199–207. JSTOR 1312741. Retrieved October 22, 2013.
  10. ^ a b c d Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1046/j.1523-1739.1994.08010072.x, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1046/j.1523-1739.1994.08010072.x instead.
  11. ^ a b c Flannery, Tim (2005). The Weather Makers. Toronto, Ontario: HarperCollins. pp. 114–119. ISBN 0-87113-935-9.
  12. ^ Kirby, Alex. "Sci/Tech Climate claims the golden toad". BBC. Retrieved 25 October 2013.
  13. ^ Eden, Phillip (1999-2013 WeatherOnline Ltd.). "Fog and Mist". Weather Online. Retrieved 25 October 2013. {{cite news}}: Check date values in: |date= (help)
  14. ^ Eden, Phillip (1999-2013 WeatherOnline Ltd.). "Dew Point". WeatherOnline. Retrieved 25 October 2013. {{cite news}}: Check date values in: |date= (help)
  15. ^ Phillips, K. 1994. Tracking the vanishing frogs. New York: Penguin. 244 p. Cited in Neville.
  16. ^ "Big Question for 2012 - What Animals Could Go Extinct?". Discovery News. Retrieved 2011-12-18.
  17. ^ Black, Richard (2010-08-09). "Global hunt begins for 'extinct' species of frogs". BBC News. Retrieved 2010-08-09.
  18. ^ Crump, M. L.; Hensley, F. R.; Clark, K. L. (1992). "Apparent Decline of the Golden Toad: Underground or Extinct?". Copeia. 1992 (2): 413–420. JSTOR 1446201.
  19. ^ "El Niño and a Pathogen Killed Costa Rican Toad, Study Finds". The Earth Institute - Columbia University. 2010-03-01. Retrieved 2012-08-16.
  20. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1073/pnas.0806368105 , please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1073/pnas.0806368105 instead.
  21. ^ a b Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1073/pnas.0908572107 , please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1073/pnas.0908572107 instead.
  22. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi: 10.1073/pnas.1105538108, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi= 10.1073/pnas.1105538108 instead.

Further reading

Wikispecies has information related to Incilius periglenes.
Wikimedia Commons has media related to Bufo periglenes.
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