A Battle Won in the War to Protect Amphibians

Being led to my grandfather’s pond, bleary-eyed from bed, I wondered why we were going outside with a pickle jar. He stooped over and submerged it under the water. What was brought up in the jar captivated and mesmerised me. “Frogspawn. They will be tadpoles soon.”

Amphibians – frogs, newts and salamanders – are facing hard times. Disease is causing their populations to decline the world over. If you are someone like me who has an affinity for amphibians, it can be difficult to read about case after case of mass die-offs. That is why many conservationists are very pleased about a recent success story in Spain.

A Fungal Disease

Before we come to the success story, we must step back a bit. Chytridiomycosis is a skin disease of amphibians caused by the fungus  Batrachochytrium dendrobatidis, which is often shortened to Bd. It is thought that Bd interferes with body functions carried out by the skin1, which causes the disease and kills the animal (Fig. 1). This is why chytridiomycosis is one of the major culprits causing the population declines in many amphibian species on every continent except Antarctica.

Upon the widespread discovery of Bd, the question begged for conservationists – what was causing the worldwide emergence of Bd, and more importantly, could we do anything about it?

Midwive-toads-Alytes-obstetricans-suffering-from-chytridiomycosis-in-the-French-Pyrenees.-Credit-MC-Fisher_0

Figure 1. Mallorcan Midwife Toads infected with Bd © Mattew Fisher/Imperial College London.

The How and Whys

There is debate over the issue of how Bd emerged and spread globally, but one school of thought is that climate change is to blame2. Others suggest that humans are responsible by introducing Bd to sites of the disease’s emergence through the trade of amphibians for pets, or between scientific laboratories3.

Human activity certainly does pose a threat through animal trade, however. At least one instance of Bd emergence, in a previously infection-free frog population on the Spanish island of Mallorca, was due to human activity3. Unfortunately, this happened with the best of intentions through a conservation initiative.

When Mallorcan Midwife Toads (Alytes muletensis) (Fig. 2) were found to be suffering from chytridiomycosis, conservationists Susan Walker and colleagues3 investigated. By looking at the DNA of both the frogs and the Bd infecting them, they managed to trace the source of the infection back to a captive breeding centre. The centre was running a breeding programme to help the threatened toads. The DNA also showed that the type of Bd was not like the type found in the rest of Europe. This meant that the Bd outbreak in Mallorca came from somewhere exotic. It was discovered that an endangered frog from South Africa, Xenopus gilli, was brought to the breeding centre, and with it came Bd3. The diseased South African frog unfortunately infected some Mallorcan Midwife Toads ready to be released into the wild.

Male-Mallorcan-midwife-toad-carrying-eggs

Figure 2. Ironically the male Mallorcan Midwife Toad carries the eggs, giving the species its name.

The Spanish Success

Luckily the outbreak of chytridiomycosis in the Mallorcan Midwife Toads was contained to just a few ponds. Furthermore, scientists were at the scene from the beginning, allowing action to be taken fast. This created the potential opportunity to eliminate Bd in Mallorca. However, no attempt to do so in the wild had ever been successful in the past, so how to go about it this time?

To tackle Bd in Mallorca, a team of conservationists undertook a combined approach4. The idea was to clear the animals of Bd, and then cleanse their ponds of any environmentally lingering Bd. So after the breeding seasons in 2009 and 2013, the team captured all the tadpoles they could from ponds that contained Bd, then quickly ran them to a laboratory where they were kept and treated with fungicides to kill the fungus. During this time, quite a radicle and perhaps controversial attempt was made to clean up the ponds. The team used the industry-standard disinfectant chemical Virkon S – to wash the rocks, crevices and everything else around the ponds. Afterwards, the treated tadpoles were returned to their ponds.

Two years later and the frogs are still Bd-free (Fig. 3). Although at one site the disease unfortunately returned. Nevertheless, this is a true victory for conservation. Not only has a frog population been saved, but the effort also serves as a proof of principle that chytridiomycosis can be eliminated in the wild.

BD_Decline

Figure 3. Mallorca Infection intensity of Bd, based on the average amount of fungus (Bd load) found at 2 ponds at Coco de sa Bova (top), and 3 ponds at Torrent des Ferrerets (bottom). The green points are samples taken during summer, and the blue points are samples taken during the spring. Adapted from (4).

A New Weapon

Despite the success in Mallorca, this is not the end of the story for amphibians. Chytridiomycosis-causing Bd is only one of many threats facing amphibians right now. A much larger effort is required to identify and help amphibian populations in trouble. Luckily we have another trick up our sleeve to aid amphibian conservation – citizen science.

Citizen science is the generation of data by the public. This can be used as a tool to alert conservationists to new outbreaks of amphibian disease and rapidly respond to curtail further widespread infections.

When asked if citizen science could be used as an effective tool in amphibian conservation, researcher Trenton Garner – a member of the team in the Mallorca success – had this to say: “[It is] a no-brainer. Citizen science can generate far more data than any researcher-only project, it raises awareness like crazy, it reinforces the importance of biodiversity to a wide swathe of the public and it trains new conservationists5.”

The success in Mallorca proves conservation to be a force in the fight against the threats facing amphibians. And with worldwide help from citizen scientists, long may amphibians live on in all of our ponds, and remain a source of biological wonder and amazement for generations to come.

References

  1. Voyles, J., Berger, L., Young, S., Speare, R., Webb, R., Warner, J., Rudd, D., Campbell, R. & Skerratt, L. F. (2007) Electrolyte depletion and osmotic imbalance in amphibians with chytridiomycosis. Dis. Aquat. Org. 77, 113–118.
  1. Pounds, J. A., Bustamante, M. R., Coloma, L. A., Consuegra, J. A., Fogden, M. P. L., Foster, P. N., La Marca, E., Masters, K. L., Merino-Viteri, A., Puschendorf, R., Ron, S. R., Sanchez-Azofeifa, G. A., Still, C. J. & Young, B. E. (2006) Widespread amphibian extinctions from epidemic disease driven by global warming. Nature 439, 161–167.
  1. Walker, S. F., Bosch, J., James, T. Y., Litvintseva, A. P., Antonio, J., Valls, O., Piña, S., García, G., Rosa, G. A., Cunningham, A. A., Hole, S., Griffiths, R. & Fisher, M. C. (2008) Invasive pathogens threaten species recovery programs. Curr. Biol. 18, R853–R854.
  1. Bosch, J., Sanchez-tome, E., Fisher, M. C., Fernandez-Loras, A., Oliver, J. A., Fisher, M. C. & Garner, T. W. J. (2015) Successful elimination of a lethal wildlife infectious disease in nature. Biol. Lett. 11.
  1. Garner, T. W. J. (2015) Email interview.
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