New genetic tools might help scientists protect vanishing species
Researchers studying highly endangered frogs found that environmental DNA (eDNA) analysis can detect both rare amphibians and the diseases they carry.
“People have used eDNA to detect chytrid before, but they hadn’t used it in the context of looking for endangered frogs,” said Corinne Richards-Zawacki, a research professor and director of the University of Pittsburgh’s Pymatuning Laboratory of Ecology.
Richards-Zawacki began studying Panamanian golden frogs (Atelopus zeteki) as part of her PhD research at the University of Michigan. At that time, the major threat to Panamanian golden frogs was overharvesting for the pet trade. But after chytrid made it to Panama, the species declined rapidly. “I became a disease ecologist out of need, rather than desire,” she said.
Conservationists successfully bred the species for the first time in captivity in 2012. That same year, Richards-Zawacki returned to Panama after her graduate studies to determine whether the frogs had become extinct in the wild. Scientists haven’t detected the species in the wild since 2009.
Detecting rare or endangered species is often difficult—especially for small amphibians that can easily hide among the dense vegetation and leaf litter in tropical rainforests. The researchers wondered if they could find any trace of the lost Panamanian golden frog—or other species in the same genus—by using the species’ molecular footprints, rather than relying on the limitations of their eyes and ears alone.
In a study published recently in Animal Conservation, Richards-Zawacki and her collaborators Caren Goldberg and Jamie Voyles used eDNA in combination with visual searches to look for three species of endangered harlequin frogs (Atelopus sp.) across western Panama. They found evidence of only one species, the variable harlequin frog (Atelopus varius), which the International Union for the Conservation of Nature lists as critically endangered. They did, however, detect chytrid fungus in most of the sites that historically had Atelopus. Despite the presence of chytrid, the variable harlequin frog persisted in sites in three regions in its historic range.
Sometimes, species only showed up when researchers used one of the survey methods—for example, they saw the variable harlequin toad on some surveys but didn’t detect it through eDNA, or vice versa. “When you get species that are so rare, detection becomes difficult,” said Richards-Zawacki. “We get more information when we use both of these techniques than when we just use one,” she said.
While the team succeeded in detecting rare Atelopus frogs, there are still challenges to the eDNA approach, especially in remote field environments. There can be compounds in the water that inhibit the detection of eDNA in the lab, and hot temperatures and natural decomposition can cause DNA to break down. While researchers can filter water samples onsite at some locations or keep them frozen at others, it isn’t always possible while working deep in the jungle.
But eDNA still gives researchers another tool to work with.
The development of the eDNA surveillance tools is just a small part of a larger research project looking into these amphibian communities. The Resilience Institute Bridging Biological Training and Research (RIBBiTR), a Biology Integration Institute funded by the National Science Foundation, includes study sites in Panama, Brazil, Pennsylvania and California to study how amphibian communities cope with environmental changes like those brought by chytrid.
“We’re developing tools to detect where frogs are now but also how these amphibian communities are changing over time,” Richards-Zawacki said.
In addition to field surveys, researchers are studying how genetics and immune defenses across populations may influence resilience in the long term. “The more we know about the patterns of how populations rebound and communities reshape after these things, the more we can understand about the mechanisms by which they are achieving this resilience,” she said.
Harlequin toads are among the most severely impacted by chytrid, and their loss will impact the ecosystem in general. Frogs eat pests that can carry deadly diseases like mosquitoes. In Panama and Costa Rica, amphibian declines due to chytrid fungus have been linked to an increase in human malaria rates.
The amphibians are also culturally significant in Panama. “These golden frogs are national treasures,” she said, which generates local pride and enthusiasm for conservation. The Panamanian golden frog is the country’s national animal, and Aug. 14 is National Golden Frog Day. Understanding where these frogs might still exist through tools like eDNA can help researchers better target conservation approaches. “We’re excited about these tools—but we’re also still developing them,” Richards-Zawacki said.
