Central American frogs defend against fungal disease

Some Central American frog species appear to be recovering from 40-year declines caused largely by fungal disease, according to new research.

The reason, the research suggests, is better skin defenses against the deadly pathogen — Batrachochytrium dendrobatidis, or Bd, — which causes amphibian chytrid disease.

Knowing the fungal disease was making its way east — from Costa Rica, across Panama, to Colombia — the researchers set out to understand the immune defenses of the frogs in its path.

They looked at skin peptides by sampling skin secretions in a number of frog species, including the bare-hearted glass frog (Hyalinobatrachium colymbiphyllum) and the common dink frog (Diasporus diastema), before and after the pathogen hit the populations.

“We were trying to understand the differences between species,” said Louise Rollins-Smith, an associate professor of pathology, microbiology and immunology at Vanderbilt University and a coauthor of the study recently published in Science. “Why were some species doing pretty well and others were much more vulnerable?”

Riding four-wheel-drive vehicles to the study sites, Rollins-Smith and her colleagues captured frogs in sterile plastic bags, injected the frogs with norepinephrine and put them in a buffer solution, and then concentrated the peptides. The frogs released defensive substances which researchers tested for their ability to inhibit the growth of the fungus in a culture dish.

What the team found surprised them. The skin secretions improved their defenses after the fungus came into the community. “We don’t fully understand yet why that is,” she said. “We might have thought once they were infected, they would have less effective defenses.”

The team then studied the fungus itself and its ability to influence lymphocytes. They found it’s just as infectious and lethal over time. “The fungus hasn’t really changed,” Rollins-Smith said. “Frogs are recovering to some extent, and they may have adapted in some way and have better defenses.”