Some female frogs play dead to avoid unwanted male advances, study says

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FILE - Common toad / European toads are pictured in a mating ball in a pond during springtime. (Photo by: Arterra/Universal Images Group via Getty Images)

BERLIN - Some female frogs may fake their own deaths in an effort to avoid unwanted male advances during mating season, according to researchers behind a newly-published study.

Female European common frogs employ a few different tactics to avoid mating, including rotating their bodies, using a call that’s similar to that of males, and engaging in "tonic immobility" – or feigning their own death. The observations were reported in a study published on Wednesday in Royal Society Open Science.

In early spring, the common frog engages in "explosive" breeding in ponds, during which several males compete and scramble to mate with a female. This breeding event is usually limited to a few days to two weeks, with males harassing, intimidating, or coercing the females into mating, according to the study authors.

Additionally, multiple males will pile onto a single female and form what’s known as a "mating ball" – which often results in the female’s death, the study authors wrote.

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It was previously thought that the females could not defend themselves against the male coercion. However, study authors Carolin Dittrich and Mark-Oliver Rödel from the Natural History Museum of Berlin found that females may actually know how to defend themselves, and with very different behaviors.

The most common behavior used by female common frogs to escape the male's grip was to rotate her own body axis, according to the study.

If another male is caught during this explosive mating season, he will give a "release-call" to indicate the mistake to the grabbing male, the study authors explained. During their research, the team observed that females also uttered two different calls: a deeper, lower-frequency "grunt" that mimics the male's "release" call, as well as a higher-frequency "squeak."

But the most astonishing behavior was feigning death, the team said. Females were observed stiffly extending their arms and legs away from their bodies and remaining immobile until the male released them – "sometimes for several hours."

"Tonic immobility in the context of mating is exceptional and very rarely observed," Dittrich said in a statement.

Dittrich added how only a few studies have linked feigning death with mating, such as in spiders and dragonflies, and that the behavior is generally used as a last resort around a predator.

The researchers suspected that these defensive behaviors have evolved to protect the female from the formation of mating balls.

"Our study shows impressively that even very common and well-studied native species can still hold big surprises," Dittrich said.

This story was reported from Cincinnati.