Male túngara frogs need to watch their back while wooing the ladies. Their sexy moves, which involve calling out while inflating their vocal sac
By using plastic robo-frogs equipped with artificial air sacs, Wouter Halfwerk from the Smithsonian Tropical Research Institute in Panama and his colleagues have figured out which cues are detected by hungry fringe-lipped bats. They made some of the faux-frogs call while puffing up their sacs, whereas others just made sounds (see video).
They found that bats preferred to attack fake frogs that emitted sounds at the same time as inflating their throat sac. But the bats were not homing in on the sight of the inflated sac: when the frogs were covered with a transparent sphere, the bats were less likely to attack them, suggesting the bats "see" the sac using echolocation.
The experiment is one of the few that documents how complex animal signals can be a disadvantage, in this case by increasing the risk of a frog getting eaten. "Túngara frog courtship signals could potentially be even more elaborate," says team member Ryan Taylor. But the threat of eavesdropping bats may have limited the evolution of a more complex display, he says.
A previous study by the team shows that serenading frogs can send ripples through water, inadvertently helping bats to locate them. Next, the team plans to look at how the combined effect of ripples, calls and pulsing vocal sacs affect bat predation.
Journal reference: The Journal of Experimental Biology, DOI: 10.1242/jeb.107482
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