Once he started to receive very fresh animals, Fisher managed to successfully grow the fungus in culture. “From that point on we could look at it's virulence, and genetics, and to start to do proper epidemiology,” he says. Fisher was finally in a position to study the genome of the disease, to try and understand how it evolved.
In 2003, Fisher and Bosch began driving around Spain looking for amphibians to sample for the disease. At the end of a long days’ hiking in the Spanish Pyrenees they arrived at a mountain lake called Ibon Acherito. They were confronted by an amphibian horror scene, a “lake of death” Fisher says. “We saw dead animals everywhere,” says Fisher. They found more gruesome scenes in other lakes in the Aspe and Lescun valleys of the French Western Pyrenees. Ever since that grisly hiking trip Fisher and his team have been regularly revisiting the lakes to monitor the health of the animals and the spread of the disease.
Meanwhile, Schmeller arrived at the tiny French Pyrenean village of Moulis, tucked away in the lush, remote Ariege area of Southern France. Moulis hosts a French national research centre, and Schmeller started work there in 2007 to monitor the area's biodiversity. Around the time Fisher and Bosch were getting to grips with rotten toads and frogs, Schmeller was investigating the population genetics of waterfrogs at the University of Mainz, Germany, and met PhD student Trent Garner through his work. Garner moved to Fisher’s lab, and realised that Schmeller, newly landed in Moulis, was perfectly poised to investigate this mysterious disease in the Pyrenees. “I was working with amphibians and genetics before, but diseases was a whole new thing to me,” says Schmeller.
They gathered together other researchers, and initiated the Europe-wide RACE project, with €1.5 million funding from the EU’s Biodiversa network, as a concerted, organised effort to understand Bd in Europe. Schmeller’s team work with Fisher in the Aspe and Lescun valleys, and also monitor eastern Pyrenean lakes every year, to see whether Bd has reached them. There they hike up to the Bassies mountain refuge in the Auzat-Vicdessos valley, and spend hours waist-deep in cool mountain lakes, collecting frogs, toads and newts. They swab them, weigh and measure them and sometimes mark them with tiny electronic tags.
So far, even though Bd has reached the western Pyrenees, the lakes Schmeller and his colleagues are monitoring in the east are disease-free, although Schmeller doesn’t expect them to remain so for much longer. “You can run but you can’t hide from Bd. It will get there in the end,” Fisher told a meeting of all RACE participants in May this year.
The end is pretty horrific for frogs, toads and other amphibians. Once Bd infection sets in, the skin thickens. This is deadly for amphibians because they absorb water and nutrients through their skin, not through the mouth like we do. The disruption in fluid balance leads to heart failure, and eventually death.
As suspects go, Bd is probably one that you’d have least pointed the finger at. The group of fungi it belongs to is an obscure species called chytrids, which normally feed on dead, decaying plants. Something clearly converted them from a vegetarian to a carnivore diet. What’s also interesting is that the disease doesn’t always wipe out amphibian populations, so something else is at play too.
Both the Penalara and the Pyrenean work show that altitude is critical to the devastating effect of Bd. Usually, midwife toad eggs laid in spring hatch into tadpoles after a few weeks. The next weeks and months see the tadpoles metamorphose into toadlets, at which point they hop off to enjoy life out of the pond. But tadpoles born in high-altitude mountain lakes do something unique: they stay as tadpoles over winter. Once summer warms the mountains briefly the following year, they continue to grow slowly. Sometimes this process can go on for several years.