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article imageDarwin’s tiny frogs could be saved from extinction Special

By Igor I. Solar     Apr 18, 2010 in Environment
Santiago - Researchers in Concepción, Chile, have succeeded in ex-situ breeding of threatened Darwin’s little frog. Good news, as scientists commemorate the anniversary of Charles Darwin’s death, which occurred on April 19, 1882.
While exploring wetlands in dense rain-forests in Lemuy (42’ 36” S - 74’ 40’” W), a small island located next to Chiloé, a large island in southern Chile on December 3, 1834, Charles Darwin came across a “pretty and curious” tiny green frog. Being a true naturalist, he made notes describing the creature, drew sketches, and collected a few specimens for later study. It turned out to be a new amphibian genus and species which was formally described in 1841 by French zoologists Duméril and Bibron and named Rhinoderma darwinii, thus honouring its discoverer.
In Darwin’s time, this may have been a rather routine encounter, probably “just another frog”, since it did not merit allusion in the text of his book “The Voyage of the Beagle”, first published in 1890. By then, the marshes of southern Chile teemed with frogs and other aquatic life.
Since they evolved about 340 million years ago until the first half of the 20th century, amphibians were very abundant worldwide. Not anymore. During the last two decades nearly 43% of the amphibian species known to science (about 6,300) have shown declining populations or are already extinct (about 168 species).
Declines in amphibian populations have been reported worldwide. They are perceived as one of the most critical threats to global biodiversity. The impact has been more severe in areas of Central America, the Caribbean and Australia. The causes of the problem are varied and include habitat destruction and fragmentation, the introduction of non-native species, climate change and increase of ultraviolet radiation (mostly B type), chemical contaminants and water acidification. A chytrid fungus (Batrachochytrium dendrobatidis) is also known to infect both wild and captive amphibians causing a fatal skin disease.
Bufo periglenes  the Golden Toad of Monteverde  Costa Rica  another casualty of amphibian declines  ...
Bufo periglenes, the Golden Toad of Monteverde, Costa Rica, another casualty of amphibian declines, is considered extinct. Formerly abundant, it was last seen in 1989.
US Fish & Wildlife Service
Two species of frogs of the genus Rhinoderma have been described as endemic to the central-south region of Chile. These are R. rufum and R. darwinii. Because they are very similar in appearance, both are commonly known as “Darwin’s frog” (in Spanish: Ranita de Darwin). Wild specimens of R. rufum were last seen around 1980. Since 2004, this frog, assessed as critically endangered, is included in the Red List of threatened species of the International Union for Conservation of Nature’s (UICN).
Dr. Klaus Busse, a Chilean-born scientist, formerly the curator of the Fish Section of the Museum Alexander Koenig in Bonn, Germany, has done extensive work in Chile and Germany to study this frog.
Dr. Klaus Busse  Darwin s frog advocate and amateur gardener.
Dr. Klaus Busse, Darwin's frog advocate and amateur gardener.
Dr. Busse collected and preserved some of the few specimens of R. rufum currently available. He is also known for developing a machine to artificially reproduce the singing of males of this frog to lure females from their hiding places in the wild. His efforts, though, were unsuccessful. There is a real possibility that R. rufum may be already extinct.
Rhinoderma rufum. There are no known photos of this living Chilean Darwin’s frog – only images o...
Rhinoderma rufum. There are no known photos of this living Chilean Darwin’s frog – only images of preserved specimens are available.
Klaus Busse
The second species, Rhinoderma darwinii, however, although rare and listed by UICN as vulnerable, is still around and can be found in forests of Southern Chile and neighbouring areas in Argentina.
Darwin s frog (R. darwinii) in its most frequent colors: bright green on top; black ventral area.
Darwin's frog (R. darwinii) in its most frequent colors: bright green on top; black ventral area.
Jaime Bosch
Scientists from the University of Concepción, Chile and the Leipzig Zoo, Germany, have recently succeeded in breeding this frog in captivity. The project, technically assisted by Dr. K. Busse, but mostly funded by the Leipzig Zoo, started in 2009 with very few individuals captured near Coñaripe, a southern location in the Chilean Lake District. The original captive broodstock was composed of 7 males and 4 females. (To see a slideshow and videos showing R. darwinii click here).
Dr. Juan C. Ortiz, Department of Zoology, University of Concepción who leads the project in Chile said to the daily newspaper “El Sur” de Concepción:
“In October (2009), the males began singing which revealed that they were reproductively active and that attracted the females." (My translation from Spanish)
Later on, courtship activities started; the frogs mated, and beginning on Christmas eve, December 24, ending December 31, thirteen tiny froglets were added to the original captive population. By February 21, they had grown to 17 mm long (head picture).
A few days ago, I contacted Dr. Ortiz to obtain an update on the status of the project. He told me:
“The results of the project, so far, have been very successful. The progeny is showing 90% survival rate. We expect to continue the project this year by breeding again the original frogs, adding further 10 adults, and, hopefully, also breeding the young frogs born in captivity.” (My translation from Spanish).
Consulted about next steps in the development of the research, Ortiz added:
“From the point of view of conservation, our objective in the third year is to reintroduce the frogs in the same places where we obtained the initial adults. Later on, we want to re-populate places where the habitat remains intact but, because anthropic factors, the local frog population became extinct.” (My translation from Spanish).
The concern about the fate of Darwin’s frog in Chile is shared by a second research team. Scientists from the Atlanta Botanical Garden (USA) are collaborating with staff of the National Zoo in Santiago (Chile) in a project to provide adequate artificial environment and breeding opportunities to captive frogs of this species.
Ex-situ breeding and captive breeding programs (also known as live gene banks) are techniques currently used to conserve and restore threatened plant and animal species. The concept focuses on captive rearing and breeding of critically endangered stocks in protected environments and requires the maintenance of multiple year classes. Frequently, a captive breeding program will take care of all of the remaining population, or a large proportion of it, for extended periods lasting several generations until the population effective breeding numbers become sufficiently large to ensure self-sustaining survival. Of course, this must be conducted in conjunction with the removal of the conditions that caused the decline of the wild population. Unfortunately, long-term ex-situ breeding may lead to problems such a decrease in genetic variation, inbreeding resulting in increased frequency of deleterious alleles and adaptation to captive conditions. Hence, conservation biologists must keep in mind the genetic constraints of working with small breeding populations and apply the necessary measures to mitigate those limitations.
Captive breeding programmes are complex, costly and labour intensive. As such, these efforts are seen as a ‘last resort’ and a proactive alternative between allowing a genetic resource to disappear and doing something to preserve it.(For additional information on threatened species and captive breeding programs for frogs click here)
Darwin’s frogs are very small. The adult male measures about 2.8 cm, while the female is a bit larger, about 3.1 cm. However, even smaller frogs exist. Among them, the “Brazilian Gold Frog” (Brachycephalus didactylus) and the “Monte Iberia Eleuth” (Eleutherodactylus iberia), from Cuba. Fully grown adults of these species measure less than 1 cm. The conservation status of these diminutive amphibians is diverse. The gold frog is considered a relatively common dweller of forests near Río de Janeiro, Brazil, while the Monte Iberia frog, the smallest tetrapod alive, is listed as “Critically endangered” (UICN) because the species distribution is very restricted, being found only in a few locations in Holguin Province in eastern Cuba, where the local fauna is threatened by continuous deforestation.
From the reproductive point of view, Darwin’s frog is very special. This species has a very unusual form of parental care. The female lays about 30-40 large (4 mm) clear eggs. The male fertilizes de eggs and looks after them by staying in close proximity. When the larvae develop enough to start wriggling inside the eggs (about 20 days post-fertilization), the male takes the embryos up into his vocal sac. Within about 3 days the tadpoles hatch, but larval development and metamorphosis continues within the vocal sac of the male. The parent shelters the tadpoles and nourishes them with viscous secretions within the vocal sac. At the end of metamorphosis the froglets move from the male's vocal sac into the mouth. A few days later, the tiny frogs emerge from their father’s mouth and start independent life. The only other species of amphibian that carries out a similar reproductive process is the probably extinct R. rufum.
The video at the top of this article shows the environment where “Ranita de Darwin” lives, associated creatures in their ecosystem, variation in coloration, ability to mimic their surroundings, and tadpole activity seen through the vocal pouches of the male.
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