Bullfrogs Aid Rapid Amphibian Decline with Deadly Pathogen--But Also Die

Amphibians are rapidly declining across the globe. Frogs are disappearing from forests, salamanders from brush and newts from streams. While there are several reasons behind this decline, the one that stands out is a disease that's spread by bullfrogs. Now, though, scientists have discovered that these bullfrog carriers can also die from the pathogen.

About 40 percent of all amphibian species are declining or already extinct. In fact, a recent study revealed that Red-Listed amphibians were disappearing from habitat at a phenomenal rate of 11.6 percent per year, which means they'll be gone from half of their habitats in about six years. This has major implications for ecosystems since amphibians act as efficient predators of insects while providing valuable nutrients to creatures further up the food chain.

Numerous factors are involved in this decline, including habitat destruction, climate change, pollution and invasive species. Another study even revealed that the introduction of oil palm plantations was decreasing the amount of rare frogs in Malaysia. Yet the fungus that the bullfrog carries plays its own role in devastating amphibian populations. The pathogen itself is called Batrachochytrium dendrobatidis, also known as Bd or chytrid fungus. It can kill amphibians and spread quickly through habitats.

In order to examine exactly how bullfrogs act as carriers, researchers raised frogs from eggs in controlled, experimental conditions. They found that at least one straight of the pathogen can be fatal to year-old juvenile bullfrogs. However, bullfrogs were resistant to one other strain that was tested.

"At least so far as the chytrid fungus is involved, bullfrogs may not be the villains they are currently made out to be," said Stephanie Gervasi, a zoology researcher in the OSU College of Science, in a news release. "The conventional wisdom is that bullfrogs, as a tolerant host, are what helped spread this fungus all over the world. But we've now shown they can die from it just like other amphibians."

In fact, bullfrogs aren't really a very good host for the fungus. First identified as a novel disease of amphibians in 1998, the fungus may have spread so far and quickly due to climate change and other stress factors rather than being transported by bullfrogs.

"There are a lot of possible ways the fungus can spread," said Andrew Blaustein, a professor of zoology at OSU, in a news release. "People can even carry it on their shoes."

The findings are published in the journal EcoHealth.