An entire population rapidly wiped out: this was the subject of Andrea Adams’s pHD thesis, which explored why Rana boylii, also known as the foothill yellow-legged frog, declined to the point of extinction in part of its habitat range in southern California.
“I started researching California amphibians in 2008,” said Adams in an interview with The Bottom Line. “I found Rana boylii to be interesting because I’d never even heard of the species before I started researching it. They used to be here and no one had really looked into why they became extinct.”
Ultraviolet radiation and habitat loss usually slowly chip away at population numbers, so Adams expected that the culprit behind the frog’s rapid extinction to be disease.
“My research consisted of a lot of field work and museum study,” said Adams. “Through an interdisciplinary analysis, I was able to identify chytridiomycosis as what killed off Rana boylii.”
Chytridiomycosis is an infectious disease caused by the chytrid fungus. It is capable of causing a 100% mortality rate in some amphibian populations.
Chytridiomycosis has wiped out several amphibian populations aside from Rana boylii, mostly in eastern North America and the Sierra Nevada. It doesn’t seem to be native to western North America.
“I think that the reason we found the disease affecting western North America populations is … the global amphibian trade,”Adams said. “Wild caught and farmed frogs are shipped all over the world, often for their frog’s legs. They’re kept in close proximity, which allows the virulence of the disease to ramp up.”
Tree frogs can contract and carry the disease, moving it across landscapes. Additionally, when frogs are transported via the amphibian trade, it can be difficult to contain the disease within specific locales.
There was a similar disease described in 2013 that affected both salamanders and frogs, especially salamanders in the Netherlands. The U.S. government responded by restricting interstate commerce in order to protect native species.
“Although some might say that legislation like this isn’t economically smart, the salamander sellers were just as happy as ecologists. They marketed their salamanders as fungus-free and charged a premium. It was win-win for everyone,” said Adams.
The U.S. Fish and Wildlife Service could potentially add provisions within The Lacey Act to regulate the global amphibian trade and protect amphibian species from virulent diseases like chytridiomycosis.
“I think there’s this conception that wildlife law has to be controversial. Sometimes people don’t see the need to regulate something without much commercial value. But wildlife legislation can be good for business and for the environment if done right,” said Adams.
Adams is currently finishing up several studies that she began in graduate school, including amphibian monitoring in Mexico and a collaboration project with the California Grizzly Study Group. She also teaches several courses in the EEMB department at UCSB and runs her own blog.