Frog love is in the air unless someone gets in the way – IndyStar

Lorena Villanueva-Almanza Published 6:00 a.m. ET July 6, 2020

Imagine attempting to broadcast romantic messages to a potential mate while another Romeo is trying the same. Now, picture you are doing this under the imminent risk of having the messages intercepted by someone who wants to turn you into dinner.

Researchers from Purdue University set speakers with frog recording sounds to find out how two male frogs send love messages to females while trying to avoid getting eaten byeavesdroppers, such asbats, or attackedbysmall biting flies called midges. Their recently published study shows females have no preference for either of the two males calling, but that the "eavesdroppers" targetthe frog whomakes the first call.

Their findings help us better understand how male frogs court the opposite sex through sound, yetstill live to croak another day.

If you are wondering if humans process consecutive sounds more like a frog with little regard to order or a midge, you might be in for a surprise. We are more midge-like.

Pug-nosed frogs in their native habitat in Panama.(Photo: Dr. Henry Legett)

You might have noticed that when two sounds happen almost in synchrony, we tend to focus our attention on the first one. We also perceive the second stimulus as coming from the same source as the first, something scientists call auditory illusions.

But, for the most part, not being able to distinguish between two sounds does not have implications for our love life, in the wayit does for frogs. For many species, including the one in the study, hearing cues are essential to finding females, as Henry Legett, a recent Purdue University graduate and leading author of the studyexplained.

The song male frogs sing to attract females is similar to how birds of paradise use their feathers to grab their love interest's attention.

Frogs are producing an auditory signal because they need to attract mates, Legett said, It wants to mate as much as possible and survive as long as possible, because that will produce the most offspring over the lifetime of this frog.

This can be challenging when two males are calling at the same time. Up until now, researchers were uncertain if females of this species could locate their preferred caller when two males are trying to hook up with them using sound.

The group of researchers was also interested in seeing if call mating attracts unwanted attention from predators. Hungry bats and blood-sucking midges, who are also trying to figure out where their next victim is, might not be able to find them because sounds of two different frogs singing at the same time are hard to identify.

Pug-nosed frogs in their native habitat in Panama.(Photo: Dr. Henry Legett)

To decipher this frog romance-espionage drama, the group of scientists set speakers playing recordings of synchronized mating calls of two frogs in an acoustic chamber. They took note on which of the two speakers would females and predators would go after.

They found female pug-nosed frogs have no apparent preference for their love partner. Because the female frogs crawled to either of the two speakers, the researchers came to the conclusion that unlike bats and midges,they are able to distinguish both songs.

What surprised us is that females are not susceptible to this illusion, said Ximena Bernal, principal investigator of this research and last author of the published paper.

On the espionage side of the affair,it turns out that both bats and midges go after the speaker that starts the mating call first, meaning they are only able to identify the first frog singing.

Synchronized calling may be riskyfor male pug-nosed frogs what could be worse than getting killed in the pursuit of love? but they don't have much of a choice: They must call if they want to charm females and pass on their genetic material to their offspring.

If a male survives and never gets eaten by a bat, but survives without ever mating, those genes are lost, Bernal said.

Kim Hoke, an animal behavior scientist at Colorado State University who was not involved with the research, says male frogs must seize the opportunity regardless of the potential downfall. She explained that pug-nosed frogs cannot mate all year-round and consequently must wait for the right conditions.

Of course, this also brings along fierce competition and like in any other battle, motivation is key for winning.

In this case, motivation might be coming from testosterone.

We think this is regulated by hormones, Bernal said. Higher levels of testosterone make males less shy.

She suspects this hormone also makes males lustful. Hoke agrees that this chemical compound could be making them bolder, as has been studied in other frog species.

Hormones or chemicals in their brains really drive this strong motivation," Hoke said, "where they're willing to put themselves at risk from predation and expend a really large amount of time and energy trying to attract females.

The Purdue study could help scientists understand how the nervous system has evolved to perceive sound.This research shows that frogs are better than bats, midges, and humans at identifying sound and that the nervous system has taken different routes during evolution, as Hoke points out.

We have this precedence affect illusion because sometime in the past it benefited us, not because that's the only way the auditory system can be built, Hoke said.

Bernal and Hoke would like to understand the details of how testosterone might make male frogs bolder and if it is always the same frog starting the call every night.

What we dont know and would be interested in studying is if its the same male, the leader, that always starts the call or if he says, Ive tried once so Ill wait for somebody else to go first. We wonder if there are braver frogs that always take the risk.

Lorena Villanueva-Almanza is the 2020 AAAS Mass Media Fellow at the Indianapolis Star. She earned her PhD from the University of California Riverside in 2019 where she studied the taxonomy and ecology of Washingtonia, a group of palms found in southern California and Baja California, Mexico. Shes on Twitter as @lorevial.

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Frog love is in the air unless someone gets in the way - IndyStar