The Sound of Love:
Research Reveals Intriguing Abilities of Female Tree Frogs
Animal Planet to Feature JMU Research on Saving Amphibians
The risk of being eaten may keep some frogs from approaching a possible mate, but it's not the only danger threatening our amphibious friends.
Research has shown a deadly fungal infection is imperiling up to one third of the world's amphibian populations. But newer research by a JMU team into a possible solution has been so promising that it will be featured in "The Vanishing Frog," a Nov. 20 special program to air at 8 p.m. on "Animal Planet."
The infection, chytridiomycosis, grows on the skin of frogs and other amphibians, inhibiting the animals' ability to absorb oxygen. Populations infected with the disease have suffered nearly 100 percent mortality rates, said Dr. Reid N. Harris, a JMU biology professor leading the research team. An Animal Planet crew, including host Jeff Corwin, visited Harris and his team in early September to film the segment in a Burruss Hall laboratory.
Scientists have estimated that the fungus is threatening to wipe out more than half of the world's species of frog and other amphibians. So how do we stop it?
A bacterial solution
While researching a fungus that attacks amphibian eggs, Harris learned that other scientists discovered bacteria found on some amphibians produced antibiotics against the egg fungus. Harris then conducted experiments applying the bacteria to adult amphibians, finding it was effective in keeping the chytrid fungus from growing on the frogs.
"It suddenly clicked that the emerging fungus killing adults was chytrid fungus and that the skin bacteria producing antibiotics against the egg fungus could do the same against the chytrid fungus," Harris said.
More recently, Harris' team completed experiments with live frogs, soaking some with a solution of the bacteria before exposing them to the fungus. The frogs who had been treated with the bacterial solution showed a 100 percent resistance to the fungus, raising hopes that the solution could be the answer to helping fight the fungus in the natural environment.
Into the wild?
With such promising results from laboratory testing, scientists across the globe have been excited at the possibility of implementing a solution to save the amphibian population.
Of course, tidy university labs are a far cry from the natural world. Implementing any bacterial solution to the ecosystems of amphibians would require much more testing and refinement, and still there are no guarantees what works in the lab will work in the wild, Harris said.
"We are cautiously optimistic that we can use bio-augmentation of beneficial bacteria to manage the disease in nature in the future," Harris said. "We need more research to discover which bacterial species to add to pond water, for example, and in what concentrations in order to help amphibians without hurting anything else."
Before any possible solution is introduced to the environment, much more research is needed, and government permits would need to be acquired. But Harris is optimistic.
"There are many products in use today for agriculture that contain 'beneficial bacteria.' I think this suggests that adding beneficial bacteria is not harmful to the environment, but further testing is needed," Harris said. "I think it is possible."
Harris' original research project was chronicled in a story for the January 2006 edition of Madison Scholar. To read more about the upcoming "Animal Planet" documentary and links to other information about the ongoing threat to amphibians, visit www.savethefrog.com.
Imagine having to choose a mate based partly on the chances of surviving the trek to make the first acquaintance.
In the world of barking tree frogs, finding Mr. Right is about much more than just good looks—or mating call volume in this case.
"It is a trade-off between the quality of the male and the risk of being eaten," says biology Associate Professor Kit Murphy, who has been studying the mating habits of tree frogs for almost 20 years.
Discovery Channel Canada was so intrigued by Murphy's research that the show filmed an interview with him in Burruss Hall in September.
So why study frog behavior? Because a scientist's job is to try to understand how the world works; "because it can help solve practical problems," Murphy said. "If we have a particular explanation or theory for how the world works, we can answer specific questions through research and then they can help us explain larger theory."
How non-human species choose mates can be applied to human interaction and mate choice, Murphy said. And studying tree frog behavior allows scientists to conduct behavioral research that they cannot do on humans.
Murphy said he became interested in researching tree frogs because of an evolving set of questions and a desire to expand upon the unknown in this field of biology. He has received grants from the National Science Foundation and the biology department at James Madison University.
Among his findings, Murphy said, is that "female tree frogs are a lot smarter then we give them credit for."
Murphy conducted this research in the Apalachicola National Forest near Tallahassee, Fla. Employing synthetic mating calls and replaying them in an outdoor play-back arena, he can begin to determine factors that female frogs consider when choosing a male partner. "Synthetic sounds make it easier to manipulate any variable," he said. "Female frogs do a lot of complex information processing."
When female frogs arrive from trees bordering the pond, they sit, listen and then move toward the male of their choice. So far, the research indicates that females prefer loud calls, more rapidly repeating calls and longer calls. The male tree frog mating call is a single sound, but different males produce calls that differ in pitch and length. If synthetic calls were constructed to match small and large males, the large males would have calls that were louder, longer and lower in frequency. In contrast, the smaller males would have calls that were shorter, higher pitched and less intense.
Recent findings show there is a conflicting preference because, while females prefer the intermediate pitched calls of medium-sized males, they are more drawn to larger male frogs. But in addition to call sound, the distance to a potential mate also is a factor. Female frogs will go farther for the call qualities they prefer, but not too far because they may be risking their lives to water snakes and turtles.
After Murphy determined what calls were preferable, another question arose: How were the females able to judge the distance to the male frog? The female could assume that the most intense sound she heard was coming from the closest male; she could determine which males calls were becoming loudest fastest as she approached the group of calling males; or she could listen for the degradation of sound as the call traveled from the male to her. But tests revealed that the female frogs used none of these methods.
The complexity of the female frogs, Murphy said, is shown through their ability to independently tell the distance to the male and how loud the male call is at the source. The female frogs are able to tell which male's calls are louder at the source, even if one male is farther away from her than the other. Murphy conducted a series of experiments where one call was louder at the male source than another, but played them so they were the same volume when they reached the female frog. The female always knew which frog was louder at the source and chose that one.
What Murphy has discovered is that the female tree frogs use complex information processing to select Mr. Right. He is currently studying Brazilian frogs in Monte Alto, Brazil, where he spends the winters with his wife, Solange Lopes-Murphy, an associate professor of exceptional education at JMU. He plans to continue his research in an attempt to understand the mate choice of frogs and maybe even answer the age old question, "Why is she with him?"
Published November 2008