When toads collide


Researchers want to know whether development is forcing two desert species to cross-breed

Sunday,  August 2, 2009 3:28 AM

By Erin Dostal



FINDLAY, Ohio -- There are some things you just don't send in the mail. That's why Terry Schwaner drove from Findlay to Phoenix to pick up a cooler filled with 400 frozen toad toes.


That's right, toad toes.


Schwaner and his wife, Lila, even made a stop in Las Vegas on the way home. They kept the specimens in their motel room, packed in dry ice they picked up at an ice-cream shop. Of course, it being Vegas, nobody asked any questions. "If you've got a cooler, they assume you've got soda or something else in it," said Schwaner, a University of Findlay researcher. All of this begs the question: Why drive 30 hours to the desert for frozen amphibian parts? Nothing less than the possible extinction of two species.


The specimens that Schwaner carried back from Phoenix will allow the herpetologist to conduct DNA analysis of Woodhouse's toad and the Arizona toad. The two species have been cross-breeding for a number of years, and researchers believe humans are to blame. Encroachment on the toads' separate habitats -- dams, condos, golf courses, etc. -- are creating artificial opportunities for the two species to mingle and mate.


Random hybridization in the wild is rare. That's why experts believe this case is influenced by humans. Brian Sullivan, a professor of natural sciences at Arizona State University and a co-researcher on the project, said the Arizona toad is less resilient to drought and interference. On the other hand, Woodhouse's toad is considered a "garbage toad" that is able to live under a variety of conditions.


Experts believe that if cross-breeding continues, the Arizona toad could disappear. "We mucked things up and caused the hybridizing," Sullivan said. "If we want to protect the Arizona toad, we need to know what we did that caused this." Turns out these little toads (these two toads, like others, are species of frogs ) also are throwing traditional ecological definitions into a tailspin. The old definition of "species" was that animals could not create offspring with each other, Sullivan said. DNA research, along with new studies on mating practices, changed that. Usually, such as with mules or ligers (tigers and lions), the mixed offspring cannot reproduce.


These toads can.


"It's like black and white making gray," Schwaner said. In this case, gray is bad because the Arizona toad could pass along weaker traits to the Woodhouse's toad, sapping its resilience. Schwaner started researching the two toads in Utah's Virgin River in the late 1990s. It was around the same time that he reached out to Sullivan, who was conducting similar studies in Arizona's Agua Fria River. The two collaborated for years and published research papers. Despite their collaborations, the two had never met in person until Schwaner drove to Phoenix in May. The researchers spent two days going out to swampy sites where the toads mate.


Sullivan looks at appearances and listens to mating calls to determine toad species. He uses a 12-point scale that measures four physical features, including stripes and spots. Schwaner, on the other hand, uses DNA to determine whether he's got an Arizona, Woodhouse's or a hybrid toad. Using the combination of methods, the two hope to determine the extent and location of hybridization. Juan L. Bouzat, a biological sciences professor at Bowling Green State University and a colleague of Schwaner's, said this kind of research is important for developing conservation methods.

"There is a drastic decline in amphibian populations throughout the world as a result of human activities," he said. "This type of research allows us to understand the processes that drive extinction." Researchers are investigating troubling deformities and dramatic population declines afflicting frog species around the world.


Some researchers see frogs as an "indicator species" for water-pollution problems that could threaten humans. But back to the cooler full of toes. Why just a digit? Using just the toes is part of the conservation plan, Schwaner said. In the past, large amounts of tissue were needed for DNA analysis. That meant removing livers and hearts. Now, a toe will do. And that lets the toad survive.


Jessica Claudio, an intern of Schwaner's, conducts much of the lab work at the University of Findlay. She said the toads tell an important story. "People will become more aware about how we affect the environment," Claudio said. "It's an area that really needs help."


Arizona Toad


Woodhouse's Toad


Woodhouse X Arizona Toad Hybrid Mix