Genetics Discovery Could Help Protect Frogs from Disease

In 2012 and 2013, researchers waded in 17 ponds across Maryland to collect tail tips from more than 300 wood frog tadpoles. They chose tadpoles because frogs still in their larval stage are more susceptible to the disease.

Back at the lab, the team looked at a gene in the major histocompatibility complex, or MHC. There are two primary classes of MHC genes (class I and class II), and both play an essential role in the immune system.

Researchers already know that MHC class I genes are critical to helping adult frogs develop immunity against viruses, but tadpoles rely mainly on class II genes. This led scientists to wonder how variations in MHC class II genes might impact a tadpole’s ability to fight off disease.

To answer this question, scientists first tested the samples they collected for Ranavirus. Though they didn’t notice any signs of disease outbreak in the ponds they surveyed, 26 percent of their samples tested positive for the virus.

Using only the infected samples, researchers looked for differences among the MHC class II genes and whether those differences corresponded to levels of infection. They found that some genetic variations were linked to less severe infections.

In other words, some MHC class II gene variants help frogs fight Ranavirus more successfully than others and, consequently, those frogs have a better chance of surviving.

Scientists can use this new knowledge to better protect wild populations and to breed more disease-resistant frogs in human care. Ultimately, research like this could help combat global amphibian declines.