A water-borne fungus that has led to the extinction of several species of amphibians that spend all or part of their life cycle in water is also threatening terrestrial amphibians. In Brazil, researchers supported by FAPESP detected unprecedented mortality among a genus of tiny frogs known as pumpkin toadlets that live in the Atlantic Rainforest far from any aquatic environments. The animals were severely infected by chytrid fungus (Batrachochytrium dendrobatidis), which causes chytridiomycosis.
The study, published in the journal Biological Conservation, shows that the fungus is also a threat to terrestrial-breeding amphibians with important ecological functions, which include controlling insects that transmit diseases such as dengue, yellow fever, and zika.
“The fungus attacks the amphibian’s skin, which is where it exchanges gas with the external environment. Infection causes a physiological imbalance, and the animal eventually dies from a heart attack,” said Diego Moura-Campos, first author of the article. The study was conducted during his master’s research at the University of Campinas’s Institute of Biology (IB-UNICAMP) in the state of São Paulo, with a scholarship from the Brazilian Ministry of Education’s Coordination for the Improvement of Higher Education Personnel (CAPES).
The investigation was conducted under the aegis of the project “Chytrid fungus in Brazil: origin and consequences”, linked to the FAPESP Research Program on Biodiversity Characterization, Conservation, Restoration and Sustainable Use (BIOTA-FAPESP) and coordinated by Luís Felipe Toledo, a professor at IB-UNICAMP and a co-author of the article.
“We’ve studied the fungus from several angles, but have rarely had the unhappy opportunity to see animals dying from fungal infection in the wild. This is the first study to show the phenomenon in Brazil. If an amphibian dies and is infected, that doesn’t mean the fungus caused its death. It might be coexisting with the pathogen without developing the disease. In this case, we were sure it was the cause of death because the animals had the right symptoms, such as weight loss, heavily sloughing skin, and very high infection loads,” said Toledo, who is also principal investigator for another project that focuses on understanding how the fungus spreads in nature.
The researchers believe direct-developing species (which reproduce on land and lack a tadpole, with terrestrial eggs hatching as fully formed miniature adults) are even less adapted to the fungus. Aquatic species have been in contact with the pathogen for longer and may have developed a degree of resistance to infection.