popular science

frogs fake death to avoid sex, new study says

Female frogs have perfected their get-out-of-sex routine which includes rolling over, loud grunting, and even, yeah… faking their deaths.

Did you know that the European common frogs (Rana temporaria) — possibly the most frequently associated with frogs in general — are known as *explosive* breeders?

With males outnumbering females, it’s not that uncommon to see 6+ males trying to mount one female during frog breeding saturnalias called mating balls. Sometimes, the female can be killed inside these mating balls which might be the reason they have developed several techniques to avoid mating.

According to researchers Carolin Dittrich and Mark-Oliver Rödel at the Natural History Museum in Berlin, females can use three key strategies for avoiding males they don’t want to mate with — either because they aren’t ready to breed or do not want to mate with a certain male.

Dittrich and Rödel published their study on October 11 in the journal Royal Society Open Science.

The researchers collected male and female European common frogs from a pond during the breeding season and divided them into tanks filled with water, so each tank contained two females and one male.

Of the 54 females that were mounted by a male, 83% of them rolled their back in water. This puts the male underwater, so it has to let go to avoid drowning.

A third of females lay motionless with their limbs outstretched for around two minutes after being mounted by a male.

“To us, it appears as if the female is playing dead, although we can’t prove it’s a conscious behavior,” Dittrich said.

“It could just be an automatic stress response.”

The team also found that 48% of the females that were mounted by males emitted grunts and squeaks. The grunts mimicked “release calls” that male frogs usually make to ward off other males from mounting them.

Overall, 46% of females who were mounted by a male successfully escaped.

Smaller female frogs, which are usually younger, were the most likely to use all three deterrence strategies, whereas larger, likely older, females were less likely to fake their death, Dittrich said.

It could be that younger females, who have lived through fewer breeding seasons, become more stressed upon being mounted by males, causing them to respond more strongly.

Although the experiments are quite different from the real-world scenario, these strategies have been seen in the wild, Dittrich said.

Faking death as a strategy to escape unwanted males has been documented in just a handful of other animals, including dragonflies, spiders, and one other amphibian species — sharp-ribbed newts (Pleurodeles waltl).

Image credit: Anne Coatesy/Shutterstock

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