The Sound of Love:
Research Reveals Intriguing Abilities of Female Tree Frogs
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?"