Female Frogs ‘Play Dead’ To Avoid Sex with Horny Males

Mating season for the European common frog can be traumatic, especially for females.

Once frogs emerge from their wintertime hibernation, mating begins in earnest. Hordes of males frantically scramble over each other to latch onto females, a process called “explosive breeding.” In the commotion, females can get hurt, or even killed — unless they play dead.

Female Rana temporaria frogs can avoid unwanted male attention by splaying their limbs and becoming immobile, researchers report Tuesday in the journal Royal Society Open Science. While many animals play dead to avoid predators, this is the first in-depth study of a frog using the tactic to evade the opposite sex of its own species.

“It’s anthropocentric to say that they’re feigning death,” said Carolin Dittrich, a behavioral ecologist at the University of Jyväskylä and study co-author who prefers using the term “tonic immobility” to describe the tactic. “But [the behavior] appears to us as dead,” she said. 

Choices, choices

Biologists long assumed that females didn’t have much choice in mating systems like these, Dittrich told The Messenger. Scores of males jockey for access to the relatively rarer females, clasping onto their backs in a position known as amplexus, which stimulates the release of eggs that the male then fertilizes. “Nobody was looking at what the females were doing,” said Dittrich.

She and her colleagues initially set out to study how males choose mates by setting up experiments where males had to choose between two differently sized females in the lab. But when she was watching the videos of the experiment, she was surprised to see females employing evasive behaviors, including some who spent minutes just laying on the floor, totally immobile. 

“At first I was afraid that somebody died,” she said. Some of the males actually dragged the seemingly lifeless females around the arena until they lost interest, after which the female would perk up again. Dittrich has also seen the behavior in the wild, suggesting it may be a common tactic.

Faking death wasn’t a fool-proof method, however, as some males persisted with mating. Still, the research upends the old view that females in this mating system don’t have much of a choice.