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Amphibians at greater risk of dehydration with climate change
Projections of increased aridity and periods of drought in the world reveal that toads, true frogs, and tree frogs could lose water up to twice as fast
Text: Fernanda Zibordi*
Art: Diego Facundini**
Frogs represent around 88% of existing amphibians and are classified as one of the most vulnerable groups to drought events because they depend on humid habitats and are sensitive to water loss - Photo: courtesy of researcher Carlos Navas
The dangers of climate change involve, in addition to rising temperatures, the degradation of ecosystems through the intensification of periods of drought. Higher levels of aridity on a global scale can drastically affect regions with rich fauna, compromising species that are sensitive to water availability. An international study published in the journal Nature Climate Change has indicated that Anura amphibians (toads, true frogs, and tree frogs) may dehydrate up to twice as fast with increasing aridity.
By mapping frog occupancy areas around the world, it was predicted that between 6.6% and 33% of the group’s habitats will become more arid around 2080 to 2100. Amphibians are the most endangered class of vertebrates, with habitat loss being the main cause and climate change the main driver.
“Most amphibians, because their skin is thin and highly permeable, dehydrate very quickly. So they have to have behavioral or physiological strategies to avoid this desiccation,” explains Rafael Bovo, who studied for a post-doctorate at USP’s Institute of Biosciences (IB) and is currently a researcher at the University of California, Riverside, in the United States. The research Bovo was part of sought to analyze the sensitivity of different species to water loss and in which parts of the world they are most at risk of dehydration.
Warming and dehydration rates
Signed by seven researchers from America, Africa, Europe, and Oceania, the study was based on a combination of different types of data, which took around three years to collect.
The first type involved spatial mapping of the regions inhabited by frogs around the world. The purpose was to identify areas converging in species richness and increases in aridity and drought predicted under intermediate and high carbon emission scenarios.
For Carlos Navas, a full professor at the IB and a member of the research team, the geographical distribution of the article’s authors was essential for the challenging task of capturing this information on a global scale.
Projected risk levels for frog species around the world due to increased aridity from high carbon emissions. Bovo highlights regions such as the Amazon, the Atlantic Forest, Europe, Central America, Australia and southern and central Africa - Graphic: Nicholas C. Wu
The other part of the data was generated through a meta-analysis (statistical evaluation tool) of studies on dehydration rates in different frog species. Among the factors that can vary the sensitivity of these animals to water loss are both their physiological adaptations and their behavior. “The skin of amphibians is something extremely ‘alive’, in other words, it is full of glands and sensors,” says Navas, explaining how this organ has structures responsible for secreting substances that protect and waterproof these animals.
Regarding behavioral strategies, the professor highlights the amount of exposure frogs get during their periods of activity and the search for hiding places as determining factors for the variation in sensitivity. “Some are active at night and seek refuge during the day, while others are active during the day and are fully exposed,” he says.
Carlos Arturo Navas Iannini - Photo: Marcos Santos/USP Images
By combining these two data categories, a biophysical model was created to simulate how long these animals would be able to remain active under different conditions of drought and heat. The process considered the kinship relationships between species lineages and the different methodologies used to obtain the data.
It's not enough just to take all the studies, you need to understand how the data is compatible, because they may have different information and different calculations. There's a lot of diversity in the methods and there needs a prior curation”
One of the different ways of measuring the dehydration rate of frogs, especially during field laboratories, is to compare them to a 'fake' model. “It's made of agar. Imagine super solid gelatin. This agar behaves as if it were a totally permeable toad. So we can compare this data from the model with that from the toads,” describes Navas - Photo: courtesy of researcher Carlos Navas
Endangered species
In addition to the projections of increased levels of aridity and dehydration, the simulations indicated that between 2080 and 2100, frog activity time could fall by half in scenarios that combine increasing droughts and climate warming – compared to those that only consider rising temperatures. This reduction can compromise the feeding, reproduction and dispersal of these animals in the environment, posing risks to the survival of entire species and lineages.
Of the regions in the world that would be severely affected, the study highlights the Amazon and Atlantic Forest biomes. “They concentrate the largest numbers of species and are regions where climate models indicate more and more drought events, whether in frequency, intensity or duration,” says Bovo. Classified as hotspots– areas of high biodiversity with a high risk of extinction – the two biomes still have endemic species, i.e. the ones that are exclusive to their regions. “Brazil is the country with the largest number of amphibian species in the world and almost half of them occur in the Atlantic Forest, and many of them only occur there,” adds the biologist.
The disappearance of frogs vulnerable to increased global aridity would lead to an imbalance in food webs, potentially impacting other ecosystems. More than this consequence, in Navas’ view, there is the risk of eliminating the great evolutionary histories of each extinct species. “It’s a loss of [scientific] information for the world. An unrecoverable story that simply ceases to exist.”
It is hoped that the study will contribute to pinpointing the main areas of climatic risk, in order to guide conservation projects and influence new research in regions with poorly studied frog faunas “Even if the work has its limitations, we have put a lot of effort into this database, and at the very least it will show us some points in the world where we need to pay more attention,” concludes the professor.
The article Global exposure risk of frogs to increasing environmental dryness can be
read here.
More information: emails navas@usp.br, with Carlos Navas, and rpbovo@gmail.com, with Rafael Bovo.
*Intern under the supervision of Luiza Caires
**Intern under the supervision of Moisés Dorado
English version: Nexus Traduções
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A reprodução de matérias e fotografias é livre mediante a citação do Jornal da USP e do autor. No caso dos arquivos de áudio, deverão constar dos créditos a Rádio USP e, em sendo explicitados, os autores. Para uso de arquivos de vídeo, esses créditos deverão mencionar a TV USP e, caso estejam explicitados, os autores. Fotos devem ser creditadas como USP Imagens e o nome do fotógrafo.