According to accepted theory on animals’ mating behaviour, females will select the more "attractive" of the males. But a new study in frogs counters that notion.

The study found that female tungara frogs are susceptible to the "decoy" effect, where the introduction of a third, inferior mate results in the female choosing the less attractive of the first two options.

The results of this study counter the rational choice models that are currently used in sexual selection theory, suggesting they may prove inadequate to explain decisions in socially complex and dynamic mating arenas.

To detect the occurrence of the decoy effect in frogs’ mating choices, researchers Amanda Lea and Mike Ryan from the University of Texas, Austin, conducted experiments using 80 female tungaras, which are known to be attracted to male calls of low frequency and long duration.

They then identified three different call variants, and measured female preference for each one (equivalent to choosing a mate).

Although call B was the preferred choice over call A, females were significantly more likely to choose the intermediate target A in the presence of the decoy.

This effect was noticeable regardless of whether the decoy call was perceived from a specific spot, or an indiscernible spot.

"In socially complex situations such as this one, rational decisions could be time-consuming, potentially resulting in lost mating opportunities or the risk of further exposure to predators," the researchers said.

The results highlight the influence of context when choosing a mate, and have significant implications for scientists’ understanding of sexual selection.

"Since the decoy effect has been exhibited in humans too, these results in frogs add support to the idea that this irrationality may have deep biological roots," they said.

The findings were published in the journal Science.