Picking a mate can be one of life's most important decisions. But sometimes people make a choice that seems to make no sense at all. And humans aren't the only ones — scientists have now seen apparently irrational romantic decisions in frogs.
Little tungara frogs live in Central America, and they're found everywhere from forests to ditches to parking lot puddles. These frogs are only about 2 centimeters long, but they are loud. The males make calls to woo the females.
Amanda Lea, a biologist in the laboratory of Mike Ryan at the University of Texas, Austin, says past studies have given scientists a pretty good idea of what the females find appealing.
"They tend to like longer calls. They also like lower-frequency calls," says Lea. "Then, the other thing that's a really big one for these gals is the 'call rate.' They love faster call rates. The faster a male can call, the better."
But in real life, love is complicated. Female frogs face countless suitors. So Lea and Ryan wondered: Would a female really always pick the male that scored highest on the froggy love-call meter?
To find out, they put female frogs in a room with some loudspeakers. From one speaker the scientists played a recording of frog call that had a really fast rate. But other features in this voice were less attractive.
Then the researchers played a second, different call for the female frogs. This voice was more attractive, but it was slower. The ladies had to make a choice.
"They have two traits to evaluate," Lea explains. "They have the call rate and they have the attractiveness of the call."
The female frogs consistently picked speed. They seemed to like the fast guy best — they crawled toward that speaker.
They researchers then repeated the experiment, but this time added a third option: a frog with a voice that was as attractive as the previously rejected option. But it was slower -- very, very, very slow.
Though the females didn't pick this loser, his mere presence had a profound effect. When he was around, the superfast guy did not win. Instead, females picked the frog they had rejected the first time around.
"They actually switch their preferences," says Lea. "So now call rate is no longer the most important thing."
They reported the finding Thursday in the journal Science. And it seems to make no sense. It's the latest example of something called the "decoy effect" — that's when adding a third, inferior option inexplicably results in the rejection of the best choice.
Scientists see the decoy effect in all sorts of decision-making — among humans and other animals, too, says David Stephens, a behavioral ecologist at the University of Minnesota.
He says it happens "in hummingbirds and bees. And the most stunning example is actually not an animal at all, but in a slime mold." (In the studies of slime mold, the organism was trying to pick the best place to grow and eat.)
What's interesting about this frog study, says Stephens, is that it found the decoy effect in something as crucial as picking a mate. "Mate choice is, for many people, the gold standard decision," says Stephens.
Lea says she really wants to understand what is going on with these frogs — are they really making an epic mistake? Maybe they're just being smart about love in ways we don't understand.
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Transcript
AUDIE CORNISH, HOST:
Picking a mate can be one of the life's most important decisions, but sometimes people make a choice that seems to make no sense at all. Humans aren't the only ones. NPR's Nell Greenfieldboyce reports that frogs seem to make irrational romantic decisions.
NELL GREENFIELDBOYCE, BYLINE: These little frogs live in Central America, and they're called tungara frogs.
AMANDA LEA: And that's because the call they make sounds very much like that it's kind of a tungara.
GREENFIELDBOYCE: Amanda Lea is biologist at the University of Texas, Austin. She says only the males make these calls to woo the females, and scientists have a pretty good idea of what the females like.
LEA: They tend to like longer calls. They also like lower frequency calls. And then the other thing that's a really big - a big one for these gals is the call rate. So they love faster call rates. The faster a male can call, the better.
GREENFIELDBOYCE: But in real life, love is complicated. Female frogs face countless suitors, and the researchers wondered, did a female always pick the male that scored highest on the froggy love-call meter? So to find out, they put female frogs in a room with some loudspeakers. From one came a voice that had a very fast call rate.
(SOUNDBITE OF TUNGARA FROG CALL)
GREENFIELDBOYCE: Fast is good, but other features in this voice were less attractive. Then the females heard a second call.
(SOUNDBITE OF TUNGARA FROG CALL)
GREENFIELDBOYCE: This voice was attractive, but it was slower. The ladies had to make a choice.
LEA: They have two traits to evaluate. They have the call rate, and they have the attractiveness of the call.
GREENFIELDBOYCE: They picked speed. They liked the fast guy best. The researchers then repeated the experiment, but this time, they added a third option - a frog with an attractive voice that was very, very, very slow. The females didn't pick him. Still, his mere presence had a profound affect. When he was around, the superfast guy did not win. Instead, females picked the frog they had rejected the first time around.
LEA: They actually switched their preferences, so now call rate is no longer the most important thing.
GREENFIELDBOYCE: This finding is reported in the journal Science, and it seems to make no sense. David Stephens is a behavioral ecologist at the University of Minnesota. He says this is an example of something called the decoy effect. That's when adding a third inferior option inexplicably result in the rejection of the best choice. Scientists see it in all sorts of decision making in humans and other animals too.
DAVID STEPHENS: In humming birds and bees, and the most stunning example is actually in a - not an animal at all, but in a slime mold.
GREENFIELDBOYCE: I'm sorry - a slime mold.
STEPHENS: A slime mold, yeah.
GREENFIELDBOYCE: The slime mold was trying to pick the best place to grow and to eat. Stephens says what's interesting about this frog study is that it found the decoy effect in something as crucial as picking a mate.
STEPHENS: Mate choice is, like, for many people, the gold-standard decision.
GREENFIELDBOYCE: So science doesn't yet know. Are these frogs making an epic mistake or being smart about love in ways we don't understand? Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.
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