If one is a torrent frog living in the mountain streams of Southeast Asia, one may have a problem with one’s love song being obscured by the din of the tumbling waters.
This is not about the amphibian’s fragile ego. The problem is that sexual vocalizations being shrouded by environmental noise can result in confusion, leading to male-on-male mounting.
“Accurate sex recognition is fundamental for successful mating,” observes the team reporting in the journal Current Biology on how concave-eared torrent frogs (Odorrana tormota) of Southeast Asia attempt to prevent inadvertent and wasteful homosexual congress.
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The concave-eared torrent frog boasts special calls to attract ladies. Credit: Zhuo Chen, Junqiong Chen, Yao Li
The concave-eared torrent frog boasts special calls to attract ladies. Credit: Zhuo Chen, Junqiong Chen, Yao LiRelated Articles
It bears clarifying that not all animals reproduce sexually. Obligate asexual “higher” animals are few but include the likes of the desert grassland whiptail, a lizard species that consists entirely of females, which may pseudo-copulate. Also, same-sex relations don’t seem to be rare in Animalia; what is unknown outside humanity so far is for a male to choose to couple with another male if there is an estrus female in range.
But if procreation requires two sexes, then the sexes have to find one another, which can be a problem.
Different species do it different ways: visual cues, chemical cues, and calls may all be tapped to improve pairing efficiency. All these may be obscured by ambient circumstances. The frogs living in the “extremely noisy” streams and rivers in southeast Asia have a specific problem with finding mates based on sound cues.
The concave-eared torrent frog is only found, these days, in the brooks of the Huangshan Mountains in northern Zhejiang, an especially noisy environment.
Of course, “accident” infers something about intentionality. Frogs specifically seem especially prone to trying it on with anything whether it moves or doesn’t.
“Among frogs, same-sex sexual behavior is widespread,” write Yatao Wu, Dawai Wu and Fang Zhang of the Anhui Normal University in China with Yongmin Li of Fuyang University. It is? Apparently so, and it is “frequently attributed to sex-recognition errors, ambiguous signals, male-biased sex ratios or the instinct to indiscriminately clasp (amplexus) any suitably sized object they encounter.”
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A Sumatran torrent frog, native to Indonesia. Credit: Faith Fitrian/Shutterstock
A Sumatran torrent frog, native to Indonesia. Credit: Faith Fitrian/Shutterstock
Okay. Frogs are not fussy, at least at one end of this encounter. The other end of the encounter, however, when erroneously clasped by a fellow froggie, yells. It emits “release calls.”
Until now, it had been unclear among the herpetology set whether frogs evolved specific acoustic mechanisms to avoid such mistakes during acoustic interactions, as would make evolutionary sense.
Now for the first time, Wu and the team report on evidence that that the concave-eared torrent frog did that very thing: It developed a specific pattern of sound combining “long” and “short” calls to avoid wasting their wonders on another male.
So what have we? The frog doesn’t seem to care much about what or who it clasps, but the recipient of the attentions seems to. Also, it is more efficient at the level of the species for the sexes to be able to identify the other one accurately.
What the team has shown, with the help of playing wild frogs tapes of their vocalizations, is that the concave-eared male torrent frog – beset by multiple challenges, including the noisy streams and an effectively male-heavy demographic imbalance – evolved a specific call that says something like “ribbit ribbit ribbit, I am a male, get off” that is designed to reduce the incidence of accidental same-sex amplexus, to their mutual detriment and that of the species. The end.