Research Stories

by Matt Crum
photos courtesy of Brian Sullivan

Brian Sullivan has been clipping toes from toads since the early 1980s. No, it’s not some type of strange hobby. The toads are not hurt. And he does release them back into their habitat along the Agua Fria River north of Phoenix when he’s done. Sullivan’s goal is to collect samples and data about the toads’ appearance.

Sullivan is a professor of evolutionary biology and herpetology in Arizona State University’s New College of Interdisciplinary Arts and Sciences. He studies the interactions between two species of toads in central Arizona. The toe clippings provide important DNA samples.

The ASU scientist is taking a close look at cross-breeding between two species of toad, the Arizona Toad and the Woodhouse’s Toad. Cross-breeding is often referred to as hybridization. Dam construction and other human activity are thought to create habitat changes that can lead to hybridization. Sullivan’s work provides evidence that this is happening between these two toad species.

Arizona Toad

So what’s the big deal? There are many outcomes possible following hybridization. Some are good. In other instances it can lead to the decline or extinction of one of the species.

The construction of Waddell Dam created Lake Pleasant. Sullivan says that changes in the aquatic habitat seem to favor Woodhouse’s Toad and work to the detriment of the Arizona Toad. ” The ASU biologist earned his doctorate in zoology from ASU in 1983 and has taught at the West campus since 1989.

Male Woodhouse's Toad, right, calling to female in water

“My data goes back to the 1980s. As a result, I can test this hypothesis by collecting new data and comparing it with data that pre-dates the 1994 expansion of Lake Pleasant,” he explains.

Sullivan is looking for certain clues. If hybridization between the toad species is due to local environmental factors, he says that the area in which hybridization is occurring should have shifted upstream as a result of the dramatic rise in the water level of Lake Pleasant during the 1990s.

Hybrid between Arizona and Woodhouse's Toads

Sullivan is gathering samples of toads at a number of sites along the Agua Fria River. In addition to the toe clippings, he makes note of other physical characteristics. For example, spotting and striping can help identify a toad as an Arizona, a Woodhouse’s, or a hybrid of the two. The ASU scientist will repeat this sample collection process during the spring of 2010.

“To increase our understanding of the evolutionary significance of hybridization, it’s important to study the dynamics of hybrid zones through time as well as among locations,” Sullivan says. “The fact that I have been collecting data on toads around the Agua Fria for such a long time gives us a great opportunity to conduct a thorough, long-term study of hybridization in relation to human-induced habitat change.”

“This type of hands-on, basic scientific research is vital to our understanding of ecosystems and how human activity affects them,” says Roger Berger, director of the Division of Mathematical and Natural Sciences in ASU’s West campus-based New College. “When our students interact with professors who are engaged in work of this nature, it inspires a new generation of researchers to investigate important questions about our environment and how we affect it.”