The richness of skin bacteria is negatively correlated with Bd loads. Color and size correspond to Jaccard dispersion values. The shape indicates the survival of the frog. Bd-negative samples were excluded. Credit: Ecology letters (2024). DOI: 10.1111/ele.14372
The pumpkin toads are in trouble. Progressively severe droughts are disrupting the microbiomes of miniature-sized orange frogs, potentially making them vulnerable to a deadly fungal disease, according to a new study by an international research team. These results suggest that abnormal precipitation patterns, which are expected to worsen due to climate change and deforestation, could disrupt mutually beneficial relationships between wildlife and microorganisms, leading to a decline in biodiversity.
The researchers, led by Penn State doctoral student Shannon Buttimer and biology professor Guilherme Becker, published their results in Ecology letters. The work was featured on the cover of the January issue of the magazine.
During a campaign sampling pumpkin toad skin bacteria for his master’s thesis, co-author Diego Moura-Campos found nine dead or dying frogs. They were later confirmed to have died from chytridiomycosis, a fungal disease caused by Batrachochytrium dendrobatidis (Bd), which poses a threat to amphibian populations worldwide. Pumpkin toads, like many other amphibians, have natural Bd-inhibiting bacteria on their skin. These microbes should help protect against the fungus, so why did these frogs die, and why all at once?
“It is very rare to witness amphibian deaths in the wild, let alone have samples collected before and during an outbreak,” said Buttimer, who is pursuing his doctorate in the Interuniversity Graduate Program from the Huck Institutes of Life Sciences to Ecology.
Buttimer explained that deforestation of this region and the Amazon rainforest has led to greater rainfall variability – increased drought duration and, conversely, periods of heavier rainfall. “The outbreak coincided with the region’s lowest rainfall in the past 60 years, so we decided to determine whether there might be a link between drought, skin microbiome and mortality.”
Using 237 skin samples collected over the course of a year, the researchers genetically sequenced the toads’ skin microbiomes and compared this information to a reference database of skin microbes identified as inhibitors of Bd, bacteria that exert a protective effect against the chytrid fungus of amphibians. . The AmphiBac database, curated by Doug Woodhams, assistant professor of biology at the University of Massachusetts Boston and 25 co-authors, contains a growing list of DNA sequences from microbes whose inhibitory properties have been tested against Bd in controlled laboratory experiments.
The researchers found that the microbiomes of toads sampled after periods of above-average precipitation were more abundant in known Bd inhibitors. In contrast, one month after the drought, the toads’ microbiomes contained fewer Bd-inhibiting bacteria. According to the researchers, this finding indicates that the drought may reduce the abundance of certain Bd-inhibiting bacteria, making the toads vulnerable to the disease. fungal.
The researchers also studied microbiome diversity metrics such as species richness and composition. Overall, the researchers found that higher levels of species richness were associated with less severity of infection. Microbiome composition also became more variable after periods of low precipitation, indicating that the toads’ microbiomes may have shifted to a state known as dysbiosis, in which they become less stable and less functional. According to the researchers, this higher variability and the loss of key protective microbes could both contribute to the increase in chytridiomycosis infections.
Although additional experimentation is needed to understand the causal mechanisms that influence skin microbiome and Bd dynamics, the researchers said this study highlights the importance of considering microbiome health when assessing endangered populations. by climate change, habitat loss and disease.
“I hope our results will encourage people to think about how deforestation and climate change break down invisible symbioses and lead to population-level consequences,” Buttimer said.
Co-authors of the study include Diego Moura-Campos, of the Australian National University; Sasha E. Greenspan, Wesley J. Neely, University of Alabama; Lucas Ferrante, Federal University of Amazonas; Luís Felipe Toledo, Estadual University of Campinas.
More information:
Shannon Buttimer et al, Skin microbiome disruption linked to drought-associated amphibian disease, Ecology letters (2024). DOI: 10.1111/ele.14372
Provided by Pennsylvania State University
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