Toads That Develop Immunity Earlier Survive Deadly Chytrid Fungus, Study Finds

A deadly fungus called Batrachochytrium dendrobatidis (Bd) has devastated frog and toad populations worldwide, but some groups eventually recover even while the pathogen remains active. Researchers led by University College London (UCL), the Zoological Society of London (ZSL) and Imperial College London say the timing of the animals' immune defences may explain why.

Published in Nature Chemical Biology, the study focused on common midwife toads around four lakes in the Pyrenees of France and Spain, where Bd had severely reduced populations. At one lake, large numbers of toads were still dying and the population was close to extinction; at the other three, populations had rebounded even though Bd remained present and continued causing some deaths.

The researchers examined antimicrobial peptides — short chains of amino acids secreted from the skin that form part of the toads' immune defence. In the recovered populations, these defences were much more likely to mature while the animals were still tadpoles, meaning they entered adulthood already protected. Bd causes chytridiomycosis, a disease that damages amphibian skin; it feeds on skin containing keratin, which tadpoles lack, so they become vulnerable only after developing into adults.

Using mass spectrometry, the team identified 1,152 peptides in the toads' skin secretions, only seven of which had been previously known. Populations whose tadpoles secreted a greater variety of peptides were thriving despite Bd outbreaks, while those with fewer peptides were still experiencing high mortality.

Senior author Professor Alethea Tabor of UCL Chemistry said many human medicines, such as penicillin, were first found in nature, and that the newly identified peptides are new leads that could eventually help address antimicrobial resistance in humans.