Glass Frogs Wooing Near Noisy Waterfalls Do A Little Dance, Give A Little Wave To Get Noticed

Just a small glass frog, living in a loonely world. Image courtesy of Rebecca Brunner

When it comes to attracting a mate, sound can be important. Some animals use specialized vocalizations to turn the eye (and ear) of their beloved (including the túngara frog, whose call unfortunately also attracts predators), but what is one to do when you’re just a small glass frog living in a noisy waterfall? New research published in the journal Behaviour has discovered that these frogs have evolved to overcome their noisy surroundings by waving at each other to get attention.

The frogs observed practicing this behavior, which the researchers described as a “dance”, were found to combine their “love songs” with the flap of a hand, wave of a foot, or a bob of the head to bolster their chances of catching someone’s eye. Dancing frogs as a means of attracting a mate has been observed in wild populations in Borneo, Brazil, and India, but this latest sighting was near a waterfall in Ecuador.

The glass frog in question, Sachatamia orejuela, joins a list of species known to double up by singing and dancing when they’re in the mood for romancing. The sighting marks the first time such a behavior has been seen in a species among the glass frog family, Centrolenidae, with S. orejuela hailing from rainforests in Colombia and Ecuador.

"A handful of other frog species around the world use visual signaling, in addition to high-pitched calls, to communicate in really loud environments," lead author Rebecca Brunner, a PhD candidate at the University of California, Berkeley, said in a statement. "What's interesting is that these species are not closely related to each other, which means that these behaviors likely evolved independently, but in response to similar environments – a concept called convergent evolution."

Convergent evolution is the same dark magic that saw crabs evolve independently five times (so far) in a famous (or infamous, depending on your crab persuasion) process coined carcinization.

This is the first time a member of the glass frog family has been seen using visual signaling. UC Berkeley 

While they may be noisy, waterfalls are the perfect habitat for S. orejuela, which almost exclusively hangs out on rocks and boulders where the spray makes them near-invisible and a slippery catch if spotted. Spotting acts of romance in a permanently moisturized, near-see-through species is no easy task, which explains why so little is known about this species' mating and breeding behavior.

The discovery came about as Brunner waded chest-deep into an Ecuadorean rainforest stream (the things we do for frog love). Hearing the call of S. orejuela, Brunner noted the small frog was signaling by waving its arms and legs and bobbing its head. The resulting footage above was captured as Brunner balanced precariously on one foot on a slippery rock. 

glass frogs wave at each other
Glass frogs blend in seamlessy to their environment, but it makes the life of field biologist all the more difficult. Image courtesy of Rebecca Brunner

"This is a really exhilarating discovery because it's a perfect example of how an environment's soundscape can influence the species that live there,” said Brunner. “We've found that Sachatamia orejuela has an extremely high-pitched call, which helps it communicate above the lower-pitched white noise of waterfalls. And then to discover that it also waves its hands and feet to increase its chances of being noticed – that's a behavior I've always loved reading about in textbooks, so it is beyond thrilling to be able to share another amazing example with the world.”

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