• Hugo

Chile and Darwin’s frog: another continent, same threats

Between the Pacific Ocean to the West and the Andean Cordillera to the East, Chile is a long and narrow country isolated from the rest of South America. But this isolation makes it a place with an astonishing, sometimes pristine, wilderness. Extending from North to South over 4,000 km, the variety of climates and habitats gave rise to many endemic plants and animals. Charles Darwin, during its famous journey aboard the H.M.S Beagle, witnessed this unique wildlife and, as usual, collected specimens of various species including a peculiar tiny frog (<4cm) looking strangely like a leaf. These same specimens were ultimately sent to France in 1841, where zoologists André Marie Constant Duméril et Gabriel Bibron named the species in honour of its famous collector: the Darwin’s frog appellation was born.

There are two species of Darwin’s frogs: the Northern Darwin’s frog -Rhinoderma rufum- and the Southern Darwin’s frog -Rhinoderma darwinii-. Actually, they were. The former is thought to be extinct (not observed since the 1980’s) and the latter is declining and threatened with extinction... The reasons why? More or less the same threats faced elsewhere in the world and notably in the Pyrenees! Habitat loss, degradation and fragmentation, infection diseases (especially amphibian chytridiomycosis due to the chytrid fungus Batrachochytrium dendrobatidis -or Bd), pollution and climate change all jeopardize the existence of R.darwinii and have likely led to the extinction of R. rufum.

Range of Darwin’s frog in Chile (Red: Southern Darwin’s frog; blue: Northern Darwin’s frog); © Soto-Azat et al. 2013

Native forest of the Reserva Huilo Huilo (Region de los Rios near Valdivia). This is the type of habitat (austral temperate Nothofagus forests) that the Southern Darwin’s frog -Rhinoderma darwinii- inhabits. Note that this species doesn’t need bodies of water for its tadpoles. ©Pinterest

All amphibians are unique, and important to ecosystem functioning and for the human society (who else can predate on mosquitoes, clean our waters from algae, and serve as food for many other animals -reptiles, birds and mammals, including us?!!). They are all valuable. But the Southern Darwin’s frog is probably even more worth saving, not only for its cuteness but also for its extraordinary form of parental care, called neomelia. After the female lays eggs on the humid floor of the austral temperate forests, the male keeps them under close surveillance until he decides to ingest them all (up to 20)! Eggs and then tadpoles develop and metamorphose in the vocal sacs of their father. When they are ready after 6 to 8 weeks, the male literally spits them up on the forest floor.

Darwin’s frog achieving neomelia: A) four eggs were laid by a female on the floor; B) this is a male Darwin’s frog just after having ingested 3 of those eggs; C) another male having ingested a lot of eggs, giving it the appearance of a ‘pregnant’ male; ©ONG Ranita de Darwin

Rhinoderma darwinii is the last mouth-brooding frog after the loss of R. rufum. The gastric-brooding frogs (genus Rheobatrachus) were already lost in Australia probably because of the amphibian chytridiomycosis. It is basically the worst disease ever witnessed as it is responsible for the greatest loss of biodiversity attributable to an infectious disease (i.e. extinction of 91 species and ongoing declines of over 500 more -of which we are aware, this is probably worse). The causative agent, Bd, is present in every continent where amphibians occur (all except Antarctic), affecting over 1000 species. Please imagine what it would be like if it were a fungus affecting over 1000 species of mammals (including us); just think about how much we would hear about it. However, very few people know this disease… Why is that? Is it because no one cares about amphibians?

Yet, a disease causing so much damage in ecosystems should be of utmost concern. It probably disturbs ecosystem functioning. How else can it be when it simply wipes out species from ecosystems? Don’t think this is something natural and we should let it be. Although we haven’t created this pathogen -Bd-, the pandemic disease would likely not exist without us. We now know that Bd originates from Asia (where it is harmless to native amphibians), and that it was spread all over the world by human movements for food, pet and science trade. Some species (e.g. those we eat) are asymptomatic carriers and when they escaped or were released into new environments, they introduced the pathogen, infecting species that have no evolutionary history with this fungus, and therefore, no proper immune defense. It is a bit like European colonists that introduced Old-Word diseases (e.g. measles, smallpox) into the New World, where their impact was much more devastating. In conclusion, the amphibian chytridiomycosis pandemic is also our fault and we must do something about it.

Last June I had the opportunity to go to Chile and take part in a project dealing with Bd on Darwin’s frog. Unfortunately, I couldn’t get the chance to see a Darwin’s frog in its natural habitat because it was winter in the Southern Hemisphere and frogs are hiding in the ground. Nonetheless, just contributing to improve knowledge to inform conservation practice was an invaluable experience. I could also discover this wonderful country, stuck between mountains and seas, and its people, quite close to nature.

Some amphibians of Chile: top and bottom left: the southern Darwin’s frog (Rhinoderma darwinii, two different morphotypes). Top right: the Chilean four-eyed frog (Pleurodema thaul, you’re looking at its back); bottom-center: The Emerald forest frog (Hylorina selvatica), and bottom right, the rosy-ground frog (Eupsophus roseus). There are 55 species of amphibians in Chile (all anurans, versus 35 in France with Urodeles), of which 37 are endemic to this country. More than half of the 55 species are at risk of extinction. ©ONG Ranita de Darwin

The natural heritage is very important for Chilean people, and despite the social crisis the country is currently facing, still lots of efforts and money are going towards evidence-based conservation. Concerning the charismatic Darwin’s frogs, a conservation strategy between Chile and Argentina was developed. That comprises the NGO Ranita de Darwin which strives to conserve not only R.darwinii and also all Chilean amphibians and their habitats, relying on scientific evidence and including community development. It is somewhat funny (actually not so much) that now I am working in the French Pyrenees on the very same disease, where chytridiomycosis contributes to the decline of the common midwife toad (Alytes obstetricans). As one can guess, this is very complex, Nature was not built so that we could understand it easily. But the least we can do is to try! And with something that complex, the best is to work together, in an international collaboration. I hope what my colleagues and I are doing here in the Pyrenees will help the Darwin’s frog in the Andeans valleys as well.

#Darwinfrog #Amphibianchytrid #Chile #Mountains

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