Review: Do frog-eating bats perceptually bind the complex components of frog calls?

"DO MY TONSILS LOOK SWOLLEN?"

Everyone's experienced a bad roommate, even the Túngara Frog, Engystomops pustulosus. Inhabiting Mexico and South America, these terrestrial frogs prefer wet habitats including tropical forests, low flooded marshland, and caves. During mating season males find shallow pools and call to females. Their mating call consists of one ~350 ms "whine" followed by a series of ~0.40-0.80 ms "chucks." While the "whine" alone suffices in attracting females, the "chucks" that follow make the call more attractive due to the frog's perceptual coupling of the sounds. While males call, sometimes unwanted, acoustic predators e.g. frog-eating-bats are attracted putting the caller at risk. Since frogs group the sounds of mating calls,  is there convergent evolution between calling frogs and bats that prey upon them?

Figure 1. Variation of calls used.
Dashed line separates calls
played simultaneously.
C = Chuck. W = Whine.

Researchers collected 10 bats from Panama for the experiment. Using 3 separate speakers, 300 different call variations from 50 Túngara frogs were played to decipher which calls bats would attract bats. A variation of single "whine" and "chucks" were tested in addition to complex calls consisting of both. In addition to separating the calls, scientists reversed the natural order of the calls and verify which portion of the complex mating call was more effective in attracting mates and predators. 

Figure 2. Mean bat responses to frog calls.
Astericks represent significantly different data.

Results conclude bats prefer "whines" significantly more than "chucks," but "chucks" alone suffice in attracting bats. In contrast, female frogs will not respond to "chucks" alone suggesting that bats are more flexible when processing mating calls than frogs. 

The experimental design was well structured, organized and executed. The only issue is the calls were too clean. In the natural habitat a cacophony of mating calls can be heard and may influence bat's frog call selection in a different way. This experiment aimed at isolating individual calls, but not a realistic approach as no environment would actually mimic this design. 

I read this article because I wanted to learn more about acoustic calling in frogs. In this case, while males are the active competitor for mating, they're also protecting females from acoustic predators. I wonder why females aren't attracted to single "chucks," but prefer calls that include them following a "whine." The entire process of male selection is a fascinating topic and by researching how other animals respond to their calls we can gain better understanding of anuran behavior. 

Jones, Patricia L.. Do frog-eating bats perceptually bind the complex components of frog calls?  J OF COMPAR PHYSIO A-NEURO SENS NEURAL AND BEHAV PHYSIO. Vol. 199 No. 4. 2013 p. 279 - 283.