How frogs use acoustics to choose a mate

Loud sounds are important in both car design and frog flirtation.

So New Hampshire biologists pulled an acoustic camera used by car designers into frog mating pools to study female preferences. Researchers now suspect that a man’s chances of becoming a father depend in part on which group he belongs to.

We humans can name our own examples of how the ho-ham guys got attracted from membership in the right group, says evolutionary biologist Ryan Kalsbik of Dartmouth College. “If Ringo Starr hadn’t been a Beatle …” he says.

The acoustic chamber provides biologists a new tool for exploring membership opportunitieswrote Calsbyk and his colleagues in June Letters on Ecology. Kalsbik admits a colleague from Dartmouth, Hannah ter Hofstede, who studied insect sounds and did not participate in this study, told him about this industrial chamber and its value to biologists.

“The high-tech setup is“ similar to what you can find on a rover, ”he says. The hula hoop-like antenna on the pole holds short microphones that supply 48 independent audio channels to location software. It uses small differences in when the same frog call reaches different microphones to calculate the frog’s location.

Calsbeek carried camera equipment and its substantial battery (sometimes “up to 800 vertical feet with 90 pounds on the back”) to 11 rendezvous pools for wood frogs (Rana sylvatica). In the pool, impatient males “make this huge chaotic sound” like a flock of turkeys. Vigorous imitation of Colsbyk on the phone – imagine like half-swallowed sounds of sound – really give the atmosphere of a bird.

Wooden frogs maintain their appearance in a crowd of squirrels beating lonely crowds in night pools where males gather and females shop. Fees begin earlier in the year as well wood frogs have a rare ability to survive the cold nest here and there in the litter of leaves, in some latitudes literally freeze with a stopped heart (CH: 21.08.13). Having thawed to life, they gather with the other guys at the pool, devouring their little warmed hearts, waiting for the women to find their way to the party.

Male wood frogs have no anatomy for sperm introduction. The eager dad struggles to grab the female and cling tightly to her so that his sperm reaches the eggs when she releases them. With a good grip the male turns mating frogs from crowdsourcing into an activity for the pair.

Such insanely skinny males can inadvertently drown females. Thus, once a female jumps into a mating pool, she may not have much choice as to who will be the father of her offspring. However, researchers have wondered, in places with more than one pool, can she choose at least one pile of snails over another? Perhaps some features of the chorus help her to stand out.

Most of the extensive research on marital preferences and flirtatious performances – a mockersings hummingbirds immersion, crickets twittering and so on – looking at one suitor who flaunts, usually for a woman (SN: 21.05.09; CH: 12.04.18; CH: 15.12.20). Instead, Calsbick’s team asked, “Does she have a favorite band?”

To see how a male’s membership in a group can give him a bonus to sexual attractiveness, researchers set up in the lab their own frog groups for females. Combining individual male serenades taken from a treasury of records by the pool, the researchers formed different trios. Some had a common tone of shrill little guys; some were mostly resounding bass performances and some were mixed.

In a video of what is called an “acoustic camera,” every spot of a rainbow drop in this pool in New Hampshire identifies the location of a male wood frog that has just called here. The colors match the decibel scale on the right. Male frogs gather in early spring to click (sounds to human ears as something in between human burping and turkey eating). However, for female wood frogs this is apparently a signal that males are available and want company.

The clearest result is that lab women seem to like the consistency of the chorus itself, whether piercing at a dominant height or deeper and more resounding. As a sign that this may be true outside the lab, researchers have usually found more egg-shaped masses, signs of mating success, floating in pools where the chorus maintains a more steady tone.

The wooden frog paper caught the attention of longtime frog researcher Michael Ryan of the University of Texas at Austin. Now he wanted to know about the feminine side of these choruses, such as how far a woman could hear the pools she could approach.

The acoustic camera itself also intrigues Ryan, who has already looked at shop windows on the internet, answering questions from reporters. For decades, he and his colleagues have studied the cries of wild frogs in a more difficult and complex way. He set up at least three fixed microphones to triangulate the sound position before night singing. Then he hoped that the few males he could track would show up and not change places. A moving acoustic camera with 48 sound inputs, he said, sounds “really cool”.

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