These Brazilian frogs sing and dance to communicate

Researchers found that Brazilian torrent frogs, an animal endemic to Brazil, combine noises and motions in a dynamic communication system.

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Courtesy of de Sá et al.
This image shows a mating couple of Hylodes japi during courtship. Hylodes japi female touching the dorsum of the conspecific male with her gular region during courtship (drawn based on images captured by video recording). Male is calling only with one vocal sac inflated, the one closest to the female (left vocal sac), also showing the visual component of his bright whitish vocal sacs. Note the female's left arm is closer to the male's head and the female's right arm is closer to his posterior body region.
Courtesy of de Sá et al.
Dance moves of the male Hylodes japi: (A) Toes posture; from resting position (above; frontal view) raising feet and holding feet up for some seconds, exposing dorsal surfaces of toes (below; frontal view). (B) Two-armed impulse; from resting position (above; lateral view) boosting the whole body forward by impulsion via an up and down movement with both arms simultaneously, moving the body forward and raising the anterior part of the body. (C) Head bobbing; from resting position (above; lateral view) performing a single down or up jerky movement with the head without lifting either hands or feet off the ground nor moving the body; it is performed preceding calls by males. (D) Head snaking; rapidly approaching a conspecific female, raising the head up (above; lateral view of the couple) moving it to alternate sides eight times (four times each side), in a snakelike motion (below; dorsal view of the male); it is performed with the throat at the level and in front of the female snout, with the frogs being very close to each other, but without touching. (E) Truncated walking (dorsal view); lowering the body and walking ahead slowly, with alternation of legs and arms; it is performed with a moving and stopping pattern; left arm is moved concomitantly with right leg and vice-versa.

When it comes to communication, Brazilian torrent frogs just can't sit still.

The amphibians not only use noisy vocal signals, like peeps and squeaks, to talk to each other, they also wave their arms and legs, tap their toes, bob their heads, and puff up their vocal sacs for show.

Researchers observed these frogs, scientifically known as Hylodes japi, performing one of the most complex communication systems known in frogs, as reported in a paper published Wednesday in the journal PLOS ONE.

If you've ever been near a frog-filled swamp on a warm summer night, you know just how noisy the hoppers can be. But Brazilian torrent frogs dwell in and around streams that aren't just trickling. These streams are noisy torrents of water (which give the frog its name), so they may have some competition for the airwaves.

That probably explains the antics of the territorial males of this frog species. When he wants to woo a female or tell another male to back off, a male Brazilian torrent frog has to make more than a vocal exclamation.

Sometimes the frogs would puff up their vocal sacs without uttering a call. These vocal sacs are a bright whitish hue, so puffing them out would flash another frog a clear signal. 

The researchers found that the frogs could puff up either one of their two vocal sacs independently, and would usually choose the one closest to an intruder or potential mate.

Other displays included complex leg or arm movements. The scientists observed the frogs lifting a leg, waving an arm and even trembling their toes in a wave-like pattern. 

These frogs might also raise or lower their bodies, or otherwise change their posture. Occasionally, the frogs would even bob just their head up or down in a jerky movement.

These stream-dwelling frogs may have even made up the new dance craze: head snaking. 

When a male wants to woo a mate, he quickly edges near her. Face-to-face, the male frog swings his head from side to side while raising and lowering it. The motion ends up taking a sort of snakelike path. This shows off the male's cream-colored throat and chest to the object of his affection.

All these intricate motions are in addition to complex vocal signals including peeps, squeals, and courtship calls. The combination of different modes of communication is a novelty in frogs, study lead author Fábio de Sá tells The Christian Science Monitor in an email.

Although the males are largely the ones performing these strange froggy calls and motions, the females get in on it in a unique way too.

During courtship, females wave their arms and legs a bit too, but the surprise came in the way they interact directly with a male.

"Previously unknown in frogs," the study authors write in their paper, "we also describe a bimodal inter-sexual communication system where the female stimulates the male to emit a courtship call."

If a female is interested in a male, she can actually stimulate his courtship calls and displays. By wiggling her limbs in specific ways and resting part of her throat on top of the male, she tells him she accepts his courtship. He will continue showing off for her with his dynamic song and dance.

Uncovering the diverse capabilities of frogs helps us "understand the world where we live," de Sá says. "We get surprised in how complex organisms can be."

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