Video: Frog princes woo with a song and a sac
鈥淩obo-frog鈥� has a way with the ladies. He has a speaker that broadcasts a realistic mating call and a shiny painted balloon that inflates and vibrates beneath his throat, perfectly mimicking the vocal sac of a real t煤ngara frog.
Researchers at the University of Texas are using robo-frog to study different components of communication between the frogs. And the Texas team has found good evidence that the striped is important for wooing females, even though they mate in the dark.
T煤ngara frogs live in the forests of northern Latin America. At night, males sing to attract females and their throats inflate. 鈥淭he sacs evolved for males to shuttle air back and forth, so they don鈥檛 have to suck in air each time they sing,鈥� says of the University of Texas in Austin.
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Since the female frogs can see very well in the dark, Ryan and his colleague Ryan Taylor thought the distinctive pattern on the males鈥� vocal sac might have another purpose as well.
Sexy sac
In experiments, females will move towards a speaker playing a recorded male mating call. But to test whether the vocal sac also played a role, the researchers created robo-frog 鈥� a resin replica of a male t煤ngara frog with an inflatable latex vocal sac.
The model is hooked up to an air pump driven by the wave on an oscilloscope, making the fake vocal sac to bulge in and out rhythmically.
To make the fake frog鈥檚 vocal sac to vibrate realistically, Taylor synthesised a male mating call and fed it into the oscilloscope. His team gave 20 females a choice between an inflating robo-frog producing mating calls and a speaker on its own.
Sixteen of the 20 were more attracted to the combination of speaker and frog, moving towards it to investigate. When the model frog鈥檚 oscilloscope was switched off, however, the females did not find it any more attractive than the speaker. This suggests that a vibrant vocal sac is crucial to finding a mate.
Taylor also tried making the vocal sac vibrate out of sync with the songs and he says this actually deters the females.
鈥淲e are particularly excited about the implications of this result,鈥� he says. The researchers think the frogs are showing something similar to the 鈥�, which shows that the shapes made by a person鈥檚 lips are relevant to the sound they are perceived to produce.
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