Human-Caused Changes Influence Frogs’ Immune System

Human influences on the environment may be making it harder for frogs to fight diseases, which could be causing their populations to decline.

In a study published in the journal Biological Conservation, researchers found that skin microbiomes as well as bacterial and fungal communities on Blanchard’s cricket frogs (Acris crepitans blanchardi) in Ohio differ depending on the frogs’ environment — whether it is residential, agricultural or in natural surroundings.

“These Blanchard’s cricket frogs have nearly gone extinct in their northern range, so we’re almost forensically trying to understand what happened,” said Mike Benard a biology professor at Case Western Reserve and coauthor of the study in a press release.

As part of the study, the team of researchers from Case Western University and the Holden Arboretum studied frogs from natural ponds surrounded by forest or prairie as well as human influenced ponds surrounded by houses, on farmland or near fields, parking lots and golf courses. The team noted physical differences in the ponds and tested their water chemistry and quality.

Next, the researchers collected swab samples from the frogs’ skin and placed the frogs in a solution that caused them to secrete antimicrobial peptides — an immune response that the amphibians excrete when they’re introduced to a pathogen.

“What we’re seeing is the bacteria on the skin can vary markedly depending on what people are doing to the environment that the frogs are living in,” said David Burke in a press release. Burke is a scientist and research chair at Holden Arboretum in Kirtland, Ohio and coauthor of the study. The researchers said that the pond’s latitude, conductivity and size also seemed to affect their microbiome.

Further, the frogs’ natural peptide secretions increased with the growth of chytrid fungus — a fungus devastating amphibian populations around the world. “This pattern suggests that in areas where land use increases the amount of the peptides these frogs produce, this particular pathogen could have devastating effects,” said Katherine Krynak, a postdoctoral scholar in Case Western Reserve’s Department of Biology and lead author of the study in a press release.

The researchers plan to study this further as well as how the environment interacts with the frogs’ genes. “By improving our understanding of the factors influencing immune defense traits capabilities, we are given the opportunity to make changes to our land management practices to better protect wildlife health,” Krynak said.

Header Image: A Blanchard’s cricket frog at Somerset State Game Area in Michigan. ©Jessica Piispanen, licencen by cc 2.0