Frogs No More Than a Memory?
Text and Photos: Javier Pinzón
I remember a camping trip to Cerro Azul (Panama) in the already distant year 2008, when I was a biology student. A twilight chorus of frogs lulled us to sleep. The memory is pure nostalgia, given that there is little chance of enjoying such a chorus nowadays. The frog population has dipped dramatically over the last thirty years.
It all began in the late 1970s, with some of the most alarming drops in amphibian numbers recorded in the remote, protected mountainous regions of Australia and Central America. It took nearly a decade for the global catastrophe to capture the world’s attention. Figuring out why amphibians were disappearing became an urgent conservation task. To discover what was happening to frog populations, researchers tested several hypotheses: pollution, increased UVB radiation, natural predators, and climate change. Meanwhile, the frog population continued to fall in many places around the world, even in untouched and protected areas.
The essential question comes down to: “How and where did this begin and what is being done to mitigate this serious problem?” Angie Estrada, a biologist at the University of Panama and a third-year doctoral student at Virginia Tech, notes that this is not a localized phenomenon, since it has been detected on every continent except Antarctica. The fungus has been reported in some 350 species of amphibians and the effects have been more devastating than similar epidemics in mammals or birds.
In 1996 and 1997 two groups of scientists, one in Australia and another in Panama, simultaneously detected a connection between the fungus and the frog mortality rate. At the same time, the National Zoo in Washington D.C. (United States) recorded the death of several South American poisonous dart frogs, apparently from a fungus.
After being isolated and cultivated for study, the fungus was found to represent a new genus and species. It was dubbed Batrachochytrium dendrobatidis (Bd) (chytrid) and, after experiments, studies, and field follow-up on the spread of the fungus, the hypothesis that Bd caused the worldwide decline in the number of frogs was accepted in 2007. The fungus lives in water, but it migrates to the frogs’ skin, where it reproduces, causing a disease known as chytridiomycosis. Since amphibians breathe through their skin, they die of suffocation when the fungus coats the skin.
How does the fungus spread? Estrada notes that the scientific community largely agrees that the fungus was found in Africa in Xenopus laevis, a species of frog that was used for pregnancy tests from the 1930s to the 1960s. After being sent around the world for these tests, the frogs were eventually released into streams, rivers, and lakes near the testing labs. The fungus would have sloughed off into the water and started to disperse, giving rise to an infestation in local frogs, which had no immunity against the pathogen.
Anurans (frogs and toads) belong to the group of vertebrates called “amphibians¬” —from the Greek amphi (dual) and bio (life), referring to the creature’s double life (a juvenile stage as an aquatic larva or tadpole and a land-based adult stage)— which makes them very susceptible to this fungus.
Efforts to conserve this group began rather late and some populations of amphibians have disappeared. A worldwide campaign was organized in 2006 to save populations not yet infected by the fungus or just beginning to feel its effects. One of the first Latin American centers for the rescue and conservation of amphibians was set up in Panama’s Valle de Antón.
Valle de Antón, a town about ninety-three miles from Panama City, sits inside a volcanic crater nearly 2,000 feet above sea level. The town’s large variety of frogs draws tourists and environmentalists alike. Its symbol is the golden frog (Atelopus zeteki), a species native to Panama.
Heidi Ross, director of the El Valle Rescue and Conservation Center, explains how the battle against this fungus began. She and her husband, scientist Edgardo Griffith, spotted the fungus in El Valle in 2006. Noticing that the number of frogs was rapidly declining, they decided not to wait for a conservation center to be established. The duo began collecting frog specimens, starting with fifteen species, housing them in two rooms of the Hotel Campestre. This measure allowed them to save many frogs in El Valle and keep alive some of the last specimens of the golden frog, which has not been seen in the wild since 2009.
The Panama Amphibian Rescue and Conservation Project (PARC) started in 2006 in Summit Municipal Park; it moved to Gamboa in 2015. Like latter-day Noah’s Arks, four containers served as “life capsules,” housing the remaining individuals of species extinct in the wild. Created by Dr. Roberto Ibáñez, this amphibian utopia was intended for ex situ conservation of species not likely to survive in their natural environment. The center has the support of the Smithsonian Tropical Research Institute (STRI) and a series of zoos and international organizations interested in the issue.
Ibáñez notes that keeping and caring for these frogs has been a challenge, given that there is little knowledge of their behavior, ecology, diet, and reproductive habits. It was necessary to begin research on all of these aspects to determine how to best help the frogs. Scientists need to figure out how to encourage animals never held in captivity to reproduce, how to recreate their natural habitat in 20-gallon glass tanks, and most importantly, how to feed them, which entails breeding crickets, flies, springtails (Collembola), cockroaches, moths, and beetles, which in turn need to be fed. To avoid inbreeding that could cause genetic defects over time, researchers have also developed a complex system of monitoring the offspring of each pair.
And what about the fungus? A group of scientists is searching for ways to combat it. Angie Estrada’s lab, associated with labs in Virginia and Washington D.C., is working with bacteria that protect frogs from the fungus. The first order of business was to establish which bacteria could live on the skin of frogs; scientists now understand that this varies across species and even within the same species. It has been learned that certain bacteria produce metabolites that provide protection against the fungus.
Some labs are experimenting with peptides in frog venom; certain frogs may produce them naturally as protection against the deadly fungus. Still other labs are looking into tolerance and resistance: if an infected frog manages to resist the fungus and survive, it may be selected to reproduce. Its genes may somehow make it resistant to the fungus, thus breeding a generation of more resistant frogs. The matter is complicated by the fact that the fungus has left few populations from which to choose breeder frogs.
Humans might be able to survive without amphibians, but we do not really know everything about the ecology of amphibians or how their absence could affect us. In addition to feeding on insects that bother us, frogs enliven our evening walks in the forest with their calls, and they are biological “canaries in the coal mine”: healthy frog populations indicate a healthy environment fit for many other species. These little amphibians are not the only creatures that are suffering; other fungal diseases are beginning to appear. For example, the biodiversity of bats in North America is being devastated by white-nose syndrome, caused by Pseudogymnoascus destructans; snake fungal disease, caused by Ophidiomyces ophiodiicola, is taking a toll; and salamanders are being attacked by Batrachochytrium salamandrivorans. The list of cases further includes fungal diseases that are sickening corals, bees, and the duck-billed platypus. The planet is telling us that it is ill and suffering. We need to listen and take urgent action to reverse this catastrophe.
