UCL and Imperial Researchers Find Chytrid-Fungus Survivor Toads Develop Antimicrobial Defenses While Still Tadpoles

Overview

Toads that survive outbreaks of one of the most destructive wildlife diseases on record mature their immune defenses earlier in life — while still tadpoles — according to a new study of common midwife toads in the Pyrenees published in Nature Chemical Biology. Researchers found that toads from recovering populations began secreting antimicrobial peptides from their skin before metamorphosis, according to ScienceDaily, giving them a head start against the chytrid fungus before they reach the life stage where the pathogen becomes lethal.

What We Know

• The study, led by Dr. Phillip Jervis of UCL Chemistry, the ZSL Institute of Zoology, and Imperial College London, with senior author Professor Alethea Tabor of UCL Chemistry, examined common midwife toads living around four lakes in the Pyrenees of France and Spain that had experienced severe outbreaks of the fungus Batrachochytrium dendrobatidis, known as Bd, according to ScienceDaily.
• One of the lakes studied was Ibón de Acherito, according to Phys.org.
• Three of the four lake populations recovered from their Bd outbreaks even though the fungus remained present, while the fourth continued to suffer high mortality, according to Mirage News.
• Using mass spectrometry, the research team identified 1,152 antimicrobial peptides on toad skin, of which only seven had previously been documented, according to ScienceDaily and Phys.org.
• Tadpoles that produced a wider variety of these peptides went on to show significantly better survival rates against Bd infection, per ScienceDaily.
• Bd kills toads and frogs by attacking keratin-covered skin, a condition present in mature adults but not in tadpoles; toads from the recovering populations matured their antimicrobial peptide defenses earlier — while still tadpoles — providing protection ahead of the vulnerable transition to adulthood, according to Phys.org.
• “The disease kills toads and frogs as they turn from tadpoles to adults. Getting mature immunity at the tadpole stage helps these toads survive,” said Dr. Jervis, according to ScienceDaily.
• “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,” Jervis told Phys.org.
• Professor Tabor said the scale of the peptide discovery was unexpected: “We discovered a far greater diversity of peptides than we expected,” she told Phys.org.
• The research also involved Dr. Kersti Karu of UCL Chemistry, along with Gonçalo M. Rosa, Kieran A. Bates and other collaborators, according to ScienceDaily.
• The work was funded by the UK’s Natural Environment Research Council (NERC) and the Leverhulme Trust, according to ScienceDaily and Phys.org.

What We Don’t Know

• None of the three reports explain why the fourth lake’s toad population failed to develop the same protective peptide profile as the other three, leaving the cause of its continued decline unaddressed.
• The reports reviewed do not specify whether the newly identified peptides have been tested for any application beyond the toads themselves, such as potential use against Bd in other threatened amphibian species.