Female túngara frogs don't get easily torn between two lovers, but when a third wheel joins the pursuit, it becomes an entirely different story.

When two male suitors, whose mating calls vary according to pitch, speed and length of note, make their call, a female túngara frog easily hops her way to the mate of her choice - the more attractive call. In a latest experiment, scientists added a third male frog to the scenario to find out what changes take place in the decision-making of a mate-searching female frog.

A team of researchers from the University of Texas at Austin and the Smithsonian Tropical Research Institute in Panama collected 80 individual female túngara frogs and presented them with different mating calls of three kinds. While the female frogs find longer and lower croaks in quick repetitions more attractive because they signify a larger and more energetic mate, they were also presented with different levels of attractiveness in voice and speed of repetition. The researchers found that a 'decoy effect' changes a female frog's preference, this is further discussed in their findings published online Aug. 28 in the journal Science.

In the experiment, the researchers placed the female frogs inside a dark and soundproofed room. They placed speakers around the room from where the male túngara frogs' mating calls where played. To see which mating call the female frogs moved closer to, the researchers planted an infrared video camera in the dark room.

Initially, two mating calls were played at a time. The female frogs were then seen hopping more toward the most attractive call with the quickest repetitions and which tended to have an intermediate tone and speed. When played with another mating call, the low but slow croak became less attractive, compared to the attractive and intermediate calls.

When the team played three mating calls at a time, the female frogs changed their minds and chose the intermediate calls over the initially attractive and quick call.

The use of a third wheel is actually similar to the "decoy effect" used by a lot of salesmen and marketers. When buying a car, for example, you may initially be presented with two options - a more expensive but efficient car and a cheaper but less efficient car. The cheaper car initially seems more appealing, but when a salesman puts in a third option - a car more efficient and more expensive than both the first two options, buyers have a tendency to choose the first.

"Maybe it's a way of simplifying decisions when you're presented with a complex scenario and too much information to process," said Amanda Lea, a graduate student at the University of Texas, and the study's first author. While they try to steer clear of predators, female túngara frogs also have to quickly select a mate from a huge number of suitors.

According to H. Carl Gerhardt, an evolutionary biologist from the University of Missouri in Columbia, the experiment shows that in a complex mating scenario, the most attractive candidate doesn't always win. However, he points out that the research doesn't show why female túngara frogs behave this way.

The researchers aim to further study exactly why these female frogs become fickle around their mates, and what the evolutionary impacts are of choosing less attractive mates.