A global amphibian ark
When I first stepped behind the scenes of a zoo’s herpetology department, as a student keeper, I knew that I would meet animals facing threats like pollution, habitat destruction, and a voracious pet trade. I wasn’t expecting to see amphibian after amphibian, tank after tank, being kept solely out of sheer, fierce hope. Safely cocooned in miniature, curated forests and streams are little communities, upon whose existence entire species depend. Members of The Amphibian Survival Alliance, a partner of Synchronicity Earth, are helping these families ride out the waves of a mass extinction event beyond their doors, hoping that one day their descendants will be safe outside the confines of these arks. The problem is that these animals are threatened by disease. That disease, chytridiomycosis, lives on in the soil of the forests and the waters of the streams long after its victims have gone; once it’s arrived – likely hitchhiking on a pet, a frog destined for a laboratory, or in some undisinfected water discarded down a drain – it is nearly impossible to eliminate. Their habitats may look pristine, but they cannot be made safe.
Chytridiomycosis is caused by two species of microscopic fungi. Batrachochytrium dendrobatidis (Bd) was isolated in 1998 from the skin of a Blue Poison Dart Frog that died mysteriously in a zoo. Then, in 2014, Batrachochytrium salamandrivorans (Bsal), literally the salamander-devourer, was identified in the Netherlands. The arrival triggered collapses of fire salamanders, killing around 96% of the country’s population.
Fire Salamander Bsal mortality © Jaime Bosch
The scale and speed of declines these fungi inflict are unprecedented and, in the wild, unmanageable. Most people think of fungal pathogens as ringworm, or athlete’s foot but certain characteristics of fungi can make them perfect pathogens. They don’t need their host to survive, it’s no problem for them to hang around, maybe even for months, waiting for another victim to walk by; their genomes are large and flexible – individuals can swap genetic material with relative ease; and some of them are staggeringly unspecific in their infection targets.
For a complex problem, creative solutions are needed
This year, humans have discovered what facing the rapid, global spread of a largely untreatable infectious disease feels like, and researchers have delivered the truly stunning achievement of creating a vaccine in less than a year. For amphibians, however, vaccination cannot provide the solution. A vaccination relies on triggering the immune system, and in many amphibians, chytrid fungi somehow avoid triggering any kind of immune response at all, making it impossible to vaccinate against. The host animal dies infested with fungus, but their cells don’t even recognise the invasion.
Midwife toad, Alytes obstetricans, mortality from a single lake in the French Pyrenees © Matthew Fisher
But, there is some hope. Creative and dedicated people all over the world have identified other possible pathways to a post-chytrid world. The disease has been eliminated in nature once; in Mallorca a Herculean effort was staged to remove all wildlife from infected ponds, treat every animal, even disinfect the rocks of the ponds themselves, and then return the clean water and wildlife. This saved the Mallorcan Midwife toad, but clearly isn’t widely replicable. Golden Bell frogs in Australia have been helped to persist alongside the fungus by researchers who slightly raised the salinity of their habitat. This makes conditions just uncomfortable enough for the fungus that transmission rates fall to a level the frogs can tolerate.
Some amphibians can resist the fungi and studying these species has made it clear that the whole microbial community around an amphibian is important in determining its fate.
Microbes are constantly fighting each other on their hosts and some actively repel Bd and Bsal, protecting their living home. There has been promising research showing that the transplantation of these microbes or the chemicals they produce might provide protection. However, one of the reasons this crisis arose in the first place was humans moving microbes around the world – we must think carefully before we do so again, even with good intentions.
Mallorcan midwife toad © Pria Ghosh
A worthy cause or a lost cause?
The challenge of dealing with chytridiomycosis could seem both impossible and to some people unimportant, unworthy of the time and money required for such a complex issue. There is, of course, a moral argument that it is simply unacceptable to stand by and watch as hundreds of species disappear from a disease that humans have spread, and continue to spread, around the world.
Amphibians are a vast and ancient branch of the tree of life; they’re stunningly beautiful, biologically fascinating, and diverse in their behaviour, their appearance and their appeal. It would be a collective failure of humanity to consign this broad and wonderful swathe of existence to a ‘no hope’ pile.