Robotic Frog’s Mating Calls Pass the Test
Because frogs filter white noise, the less-than-realistic mating calls of a robotic frog were able to hoodwink females.
By Evan Ackerman, IEEE Spectrum - Filed Jul 16, 2013

In my admittedly limited experience, no species (especially not humans) is particularly clever when it comes to properly interpreting mating calls. Let’s take the túngara frog as an example, because someone made a robotic one, so we can talk about it. The female túngara frog (they can be found hopping around most of Central America) relies on vocal and visual displays from male frogs to find a suitable mate, but researchers have made a “rather bizarre” discovery that a robotic version of the frog can attract females by hacking into their evolutionary aptitude for filtering out white noise.

The robot can duplicate two sounds (a “whine” sound and a “chuck” sound), as well as a physical expansion of its vocal sack. Biologists at the University of Texas at Austin and Salisbury University used the frogbot to experiment with how females react to different combinations and timings of the sounds. This is all a little bit confusing, so here’s a handy chart-thing specifying how to seduce a female túngara frog. Trust me, one day, this may save your life:

  • “Whine” sound: meh.
  • “Chuck” sound: meh.
  • Vocal sack expansion: meh.
  • “Whine-chuck” sound: ooh la la…
  • “Whine” with late “chuck” or vocal sack expansion: meh.
  • “Whine” with late “chuck” and vocal sack expansion: ooh la la…
  • “Whine-chuck” and vocal sack expansion: Hot damn!

The thing to notice here is that the whine with late chuck and vocal sack expansion is just as effective at seducing a female frog as a nicely synchronized whine-chuck. Forgive me for the giant block quote, but not being an expert on frog behavior or evolution (bringing the things I’m not an expert on today to three), I’ll just go ahead and let the researchers explain why you should care about all this frog flirtation:

“It never would happen in nature, but it’s evidence of how much jury-rigging there is in evolution, that the female can be tricked in this way,” said Ryan, the Clark Hubbs Regents Professor of Zoology in the College of Natural Sciences at The University of Texas at Austin.

Ryan compared the phenomenon to what’s called a “continuity illusion” in humans. If loud enough white noise is played in between a pair of beeps, humans will begin to perceive the beeps as a continuous tone. It’s not fully understood why this happens, but it’s probably a byproduct of our brains’ useful ability to filter out background noise.

Túngara frogs are challenged by an auditory world similar to what confronts humans in noisy environments (what’s called the “cocktail party problem” by cognitive scientists). At breeding choruses there is a lot of noise and cross talk, with sounds and images of several males reaching the female at different times. The females need to extract meaningful information from all of that. Ryan said it’s plausible the neural mechanisms that enable them to correctly parse these stimuli in nature are being hijacked by this artificial scenario.

“We need to be able to hook things together perceptually in unexpected ways to extract meaningful stimuli from a lot of noise,” said Ryan. “So what we think is happening here is that the vocal sac, the visual cue, is working kind of like the white noise, giving perceptual continuity between these two sounds, binding the temporally displaced whine and chuck together.”

Ryan said that although the frogs’ aggressive search for meaning leaves them open to being tricked by clever researchers, it could also enable more flexibility in complex situations. He believes it may have a much longer-term evolutionary advantage as well.

“It’s an example of how complex traits could emerge from simpler ones,” he said. “In this case there’s no obvious advantage to these two behaviors being hooked together in this way, but think of how you can take a muscle and move its insertion on the bone and have a great influence on speed. You didn’t get the evolution for these bones and muscles all at the same time, but just by making a change or adding a muscle, now you change the functional coupling. You end up with something really complex, but it evolved in a really simple way. I think in this case we may be seeing an example of how that could happen.”

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