A water fungus that has led to the extinction of many species of amphibians with part or all of their life in water also threatens terrestrial frogs. A team of researchers supported by FAPESP found in the Atlantic Forest an unprecedented mortality rate of frogs developing far from the aquatic environment. Amphibians are infected with a high load of chytrid fungus (Batrachochytrium dendrobatidis), caused by chytridiomycosis.
The studying, published in the magazine Biological Preservation.
“It is a fungus that lives on the skin of amphibians, where they exchange gas with the atmosphere. When an infection occurs, there is a physiological imbalance and the animal ends up dying of a heart attack”
;, explanation by Diego Moura-Campos, first author of the article, conducted during his master’s degree at the Biology Institute of the University of Campinas (IB-Unicamp), with a Coordination college for the Improvement of the Older Age of Personnel (Capes).
The investigation is being conducted under the project “ The chytrid fungus in Brazil: from its origin to its consequences ”, Linked to the BIOTA-FAPESP Program and co-authored by Luís Felipe Toledo, professor of IB-Unicamp, who also signed the study.
“We study the fungus in many ways, but we rarely have the unpleasant opportunity to see animals dying in the wild from infection. This is the first study to show it in Brazil. If an amphibian dies and becomes infected, it does not mean that it died from the fungus.He can live well with the pathogen and not develop disease.In this case, we determine the cause of death because the animals have symptoms of disease: rickety, with loose skin and a very high load of infection ”, says Toledo, who is organizing another project focused on understanding how the fungus spreads in nature.
The researchers believe that the direct development of the species, that is, those that have gone through the entire life cycle of the world, without going through the tadpole stage, are even less suited to the fungus. Because they take longer to interact with the pathogen, aquatic species can create some resistance to infection.
The dying was observed by Moura-Campos while researching the Serra do Japi Municipal Biological Reserve, in Jundiaí (SP), between May 2018 and May 2019. Notably, the dying or dying individuals of the species Brachycephalus rotenbergae (sapinho-pingo-de-ouro) was found after an atypical drought in the State of São Paulo.
“These animals are very small and hard to find. When they die, they are about to rot. Finding nine of them dead or sick in a short time, as happened, suggests that many more may have died ”, said Guilherme Becker, a professor at the University of Alabama, in the United States, another participant in research.
According to the researcher, who is also a visiting professor in the Grgraduate Program in Ecology at Unicamp, the study showed that the acceleration of global climate change in the coming decades should increase the incidence of this type of disease, which the causes may develop into more malignant strains., including due to the emergence of hybrids, as the previous work of the group has shown.
“Due to the lack of soil moisture in the forest where they live, these animals may be hydrated in streams and more infected with the fungus than before,” he said.
Another theory raised by the researchers is that periods of thirst can compromise the frog’s immune system and make them more vulnerable to the fungus.
Cosmopolitan pathogen
Originally from Asia, the fungus is likely to have spread around the world due to the frog meat trade. Species such as bullfrog (Aquarana catesbeiana), used for this purpose, is resistant to the fungus and can carry it without being infected.
An article published in the magazine Science in 2018, of which Toledo was one of the authors, it was emphasized that the fungus left the Korean peninsula and spread to other parts of the world in the early 20th century.
Another study in which the Brazilian participated also estimated that the fungus led to a population decline of 501 amphibian species worldwide. In Brazil alone, at least 50 species or populations were affected, 12 of which were killed and 38 declined.
“Amphibians are essential for the functioning of ecosystems. Their biomass is large in forests. They serve food for a variety of other animals, eat arthropods in nature, control invertebrates that community.When it comes to aquatic organisms, most are medicinal plants in the tadpole stage and consume phytoplankton, which can occupy aquatic environments if not for tadpoles.These animals cross aquatic organisms and terrestrial ecosystems, so when chytridiomycosis occurs, the impact is huge, ”Becker said.
As an example, the researcher recalled a recent study in which North American and Panamanian researchers demonstrated the association between the fall of amphibians in Costa Rica of infection in B. dendrobatidis on the increasing prevalence of malaria in the 1990s and 2000s in Costa Rica.
The team emphasizes the need to continue observations in recent years, in order to more accurately assess the true impact of chytridiomycosis on amphibian populations here and elsewhere.