Common midwife toad populations that recover after outbreaks of the chytrid fungus Batrachochytrium dendrobatidis (Bd) appear to mature their skin peptide defenses earlier, giving young toads better protection as they pass through the vulnerable transition from tadpole to adult.
The study examined common midwife toads from four Pyrenean lake populations with different disease outcomes. One population remained in an epizootic state, with high infection intensity and continuing mortality, while three had shifted toward more stable coexistence with the pathogen.
To investigate the difference, the UCL-led team used liquid chromatography-tandem mass spectrometry to profile antimicrobial peptides secreted from the animals’ skin. Skin secretions were collected from tadpoles and recently metamorphosed toads, then analyzed using a peptidomics workflow that combined de novo sequencing, antimicrobial peptide database searching, and a reference skin transcriptome. The approach identified 1,152 high-confidence mucosal peptides, revealing a much broader peptide repertoire than previously described for the species.
“We discovered a far greater diversity of peptides than we expected,” said senior author Alethea Tabor in UCL’s press release. “We now need to understand how they work to control pathogens and which ones are anti-microbial.”
The key distinction was not simply whether the toads had antimicrobial peptides, but when those defenses matured. Populations that had recovered from Bd outbreaks were more likely to show diverse, mature antimicrobial peptide profiles already in the tadpole stage. In the population still experiencing heavy disease, recently metamorphosed animals were more likely to retain a lower-diversity, immature peptide phenotype deficient in anti-Bd peptides.
“Our study shows species that have declined heavily from this disease can still recover. They have the tools to fight off infection – it just depends on timing,” said lead author Phillip Jervis in the press release. “Getting mature immunity at the tadpole stage helps these toads survive and the population to continue.”
The team also tested selected alyteserin peptides against Bd in vitro, finding that only some inhibited fungal growth. Confocal microscopy with fluorescently labeled peptides suggested that active alyteserins entered fungal cells, pointing to an intracellular mode of action rather than a simple surface effect.
The authors say the next step is to understand what controls early immune maturation, including genetic and environmental factors. “This could be down to genetics or environmental factors such as temperature or the presence of trout – a major danger for tadpoles that could drive them to develop into adults faster so they can leave the water, meaning less time for their immune system to develop,” said Jervis.
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