Study claims female frogs fake their own death to avoid unwanted male attention: 'Tonic immobility'

It looks like unwanted male attention doesn't just exist in our world but in the animal kingdom too! A new study published in the journal Royal Society Open Science on Wednesday discovered that European common frogs (Rana temporaria) went to great lengths to avoid attention from the opposite sex. 

“It was previously thought that females were unable to choose or defend themselves against this male coercion,” Dr. Carolin Dittrich, who co-authored the study with Dr. Mark-Oliver Rödel, told The Guardian. But it looks like the female European common frogs "may not be as passive and helpless as previously thought." 

Funnily enough, Dittrich and Rödel's study is titled "Drop dead! Female mate avoidance in an explosively breeding frog." In the study, researchers placed the frogs in tanks during breeding season where each tank contained two females and one male after which they filmed the frogs for an hour. The results obtained were presented after studying 54 female frogs. 

During early research, they tried to determine whether male frogs prefer a particular female body size specifically, whether they were choosing female mates with bigger bodies. But they soon learned that size didn't matter to the males and they were interested in all of the females.

This species of frog engages in an "explosive" breeding event when the season is short. So the males fiercely compete for access to females and this results in harassing or forcing the females into mating. It can get so aggressive that they end up in "mating balls" where several males cling on to the female. Dittrich, an evolutionary and behavioral ecologist who conducted the research as part of the Natural History Museum Berlin, told ABC News that this can be dangerous and even lead to their death!

Fortunately, the females fight back with three primary avoidance behaviors. The most fascinating and extreme is "tonic immobility," or feigning death which is a behavior typically used in the animal kingdom to avoid predators. Here their outstretched limbs became stiff and they did not react to male attention.

"Tonic immobility may be a better option for a female than fighting her way out," Dittrich and Rödel wrote in the study, "as any movement in a large mating group automatically attracts the attention of further nearby males and thus increases the probability of a mating ball formation."

Another method included "rotation," a turning motion used to escape a male's grip, usually used more successfully by smaller females. The third was a "release call," a sound that emulates the grunting noises male frogs make. By imitating to be male frogs they trick the males into letting them go!

The researchers said that further studies should be conducted to learn more about their mating rituals especially to learn whether smaller female frogs are consistently more successful at escaping mating scenarios, as their research suggested.

“In the real world, we often observe the formation of mating balls, but also that females can more easily dive away because there is more structure and places to hide. I think even if we call this species a common frog and think we know it well, there are still aspects we don't know and perhaps haven't thought about," Dittrich said.