One of the biggest challenges in coordinating global wildlife conservation is treating animals affected by diseases across countries, let alone across the entire world. A fungal infection called chytridiomycosis – caused mainly by the fungus Batrachochytrium dendrobatidis – has spread onto every continent, causing the extinction of about 90 amphibian species and the decline of over 700 more. The severity and scale of this infection led Anthony Waddle of the University of Melbourne and Macquarie University, Australia, and a large team of researchers from New Zealand and Australia to determine treatments for infected animals. To test a treatment and discover more about the disease, the team studied the green and golden bell frog (Litoria aurea) – a species listed as Endangered in Australia as a direct result of the fungal infection. However, the researchers first needed to determine whether frogs choose warmer temperatures that reduce or eliminate fungal infections over a cooler environment which allows the fungus to thrive.
For this, the researchers split the frogs into different groups, placing each group in separate aquaria for 15 days and swabbing each frog every 5 days to determine the amount of fungus on their skin. One group of frogs was infection free and were allowed to choose the temperature they liked best, while another group was allowed to do the same but had been infected by the fungus. The team discovered that fungus-infected frogs chose to stay in warmer areas within their aquaria, probably to clear the infection, while uninfected frogs showed no preference for what temperature they stayed in. At the same time, the researchers placed other infected frogs in either constantly warm (26.4, 29.1 or 31.0°C) or constantly cool (19°C) aquaria. The team found that infected frogs that stayed in constant warm temperatures had less severe fungal infections than infected frogs that stayed at a constant low temperature. Waddle and colleagues suggest that the cooler temperatures led to more severe infections because of the cold-loving nature of the fungus.
Next, the team wanted to determine whether frogs could become resistant to the fungus. They placed frogs infected with the fungus into a chamber set at 32°C for 14 days to clear the infection. They then re-infected the frogs and monitored them to see how many survived. The team discovered that frogs that cleared their infection in the hot environment were 23 times more likely to survive a second infection than frogs experiencing their first infection. The researchers concluded that previous infections could cause a lasting resistance to the fungus.
Finally, the team aimed to create an inexpensive treatment for frogs infected with the fungus. To do so, they constructed aquaria which contained smaller separate greenhouses with black-painted masonry bricks inside for the frogs to live in, shading some of the aquaria with a cloth while others were left in direct sunlight. They placed groups of frogs within the aquaria for 15 weeks and regularly checked the frogs’ body temperature and habitat choice and took skin swabs (to determine the amount of fungus). The scientists found that frogs were 4 times more likely to be found in the greenhouse than in the rest of the aquaria, showing that the frogs preferred the greenhouses. The unshaded, warmer greenhouses allowed the frogs to increase their body temperature to around 30°C, resulting in a lower intensity of fungus on their skin. The team concluded that the infected frogs chose to stay in warmer temperatures that kill the fungus.
The researchers showed that the frog greenhouses allowed frogs to reach a high enough body temperature to clear the chytridiomycosis infection. Most importantly, however, the team showed that wildlife managers and the public can use readily available and inexpensive materials to construct frog greenhouses – helping these endangered amphibians survive.
