Amphibious Alliance

April 11, 2019

Zoo scientists testing wild amphibians for chytrid fungus

Lions. Elephants. Chimpanzees. African dogs. Mountain gorillas.

Rachel Santymire, Ph.D., director of Lincoln Park Zoo’s Davee Center for Epidemiology and Endocrinology, has studied wild and captive species from every corner of the world via hair, blood, nail, semen, urine, and fecal samples. By analyzing the stress and reproductive hormones in biological materials, she monitored the pregnancy until the birth of a critically endangered eastern black rhinoceros at the zoo in 2013 and, since 1998, has supported the reintroduction of endangered black-footed ferrets in several Great Plains states.

But several local amphibians proved extra slippery.

In 2015, Santymire and a team of zoo scientists began studying the relationship between stress and chytrid fungus, a pathogen that has devastated amphibian populations worldwide, in Chicagoland. Testing for the fungus went by the books—after capturing individual amphibians, zoo scientists simply swabbed their stomachs and limbs, released them back into the wild, and then sent the samples to a lab for analysis.

Collecting the biological material necessary for stress analysis, on the other hand, required some innovation.

Initially, Santymire “expected to just find them in the water and pick them up. Then, when they peed on us, which is what my favorite amphibian, the toad, does to escape predators, we could collect their urine and analyze it.”

In theory, “that would’ve worked perfectly,” she adds. In reality, that did not happen, not even with the toads. Rather than resorting to more invasive techniques—like using a catheter to collect urine, taking blood samples, or waiting for days for them to defecate—she invented a completely new hormone-gathering technique.

“The largest organ in the body is actually the skin. It responds to hormones and even produces its own hormones,” says Santymire. “So we decided to just swab their skin, and, lo and behold, we got cortisol, the main stress hormone.”

Thanks to her new technique, nicknamed “frog swabs,” simultaneously checking amphibians for stress and chytrid fungus has never been easier. But the two analyses also share another critical relationship: Higher stress levels can suppress the immune system, leaving individual amphibians more susceptible to the deadly pathogen.

Out with the New, in with the Old

In 2016, Santymire began applying frog swabs to a woodland restoration project in southern Lake County along the Des Plaines River—an area which had sites that tested positive for chytrid fungus.
Historically, the woodlands followed a natural pattern: Young trees aged. Wildfires burned. New saplings sprouted. Repeat.

The flames helped shape the plant composition of the woodlands, preventing less-fire-adapted trees from shading out oak seedlings and saplings in the understory. And once the fires burned out, the plants bloomed anew, followed closely by native animal species living in the untouched woodlands. But as urbanization spread through northeastern Illinois, human management ended the natural phenomenon at the expense of individual species dependent on the cycle.

The Lake County Forest Preserve District has partnered with several local organizations to selectively reduce overhead canopy in important oak woodlands so more sunlight can reach the forest floor, decrease tree density so younger oak trees can establish, and remove invasive understory that out-compete native species.

For the past three years, Santymire and her colleagues have monitored the effects of those changes on seven native amphibian species already living in the region—blue-spotted salamander, tiger salamander, chorus frog, northern leopard frog, American toad, bullfrog, and green frog—as well as the wood frog and spring peeper, two species that were reintroduced to the woodlands as part of earlier wetland restoration research.

“Different amphibian species use the habitats in different ways,” says Santymire. “Some are fully aquatic. Some lay eggs in the water. Some live in the water and then, through metamorphosis, move onto land. Because of the unique ways they interact with their environment, they can tell us about the landscape’s health at different levels.”

The restoration effort and wildlife study will continue for several more years, but the early results look promising. Amphibian richness, the number of unique species, has improved in most restoration sites, wood frogs have increased the number breeding areas within the reintroduction site, and the other amphibian populations have adjusted accordingly.

While chytrid fungus still lurks in the woods, the coalition hopes the project—namely, decreasing tree density by 60–80 percent and increasing canopy openness by 10–50 percent—will create an improved habitat for the amphibians, which will reduce amphibian stress in the area and increase the species’ chances of overcoming the pathogen.

If that happens, it could provide a new model for countering the fungus around the globe.

Amphibians Among Us

Meet the nine amphibians living in Lake County’s oak woodlands and download the handy illustrated guide for your next adventure. Illustrations by Ashley Bedore.

Ecological Allies

The zoo’s conservation partners in the restoration project include:

  • Lake County Forest Preserve District
  • Chicago Academy of Sciences/Peggy Notebaert Nature Museum
  • Morton Arboretum
  • Illinois Nature Preserves Commission
  • Illinois Department of Natural Resources
  • U.S. Fish and Wildlife Service’s State Wildlife Grant Program