European female frogs fake their own death to avoid mating with aggressive males

During breeding season, multiple male frogs will often cling to a single female in a dangerous formation known as a “mating ball.” Credit: Carolin Dittrich

“No means no” doesn’t work too well for female European common frogs. These poor ladies risk getting trampled to death during the much too heated mating season. In response, these clever creatures have developed a surprising repertoire of survival tactics to fend off their persistent suitors, including a dramatic death-defying act.

Female Frogs’ Survival Tactics

The European common frog’s mating season is a high-stakes sprint, not a leisurely stroll. It’s crammed into a mere two weeks each spring. So, these amphibians engage in a frenzied reproductive ritual. With males far outnumbering females, competition is fierce, often leading to chaotic “mating balls” that can be deadly for the females.

Researchers at the Natural History Museum in Berlin observed that female European common frogs (Rana temporaria) employ three key avoidance behaviors during the short and intense breeding season. This behavior is crucial for their survival as the numerous and aggressive male frogs can drown or crush the females.

This female frog pretends to be dead to ward off an aggressive male. Credit: Carolin Dittrich.

Researchers collected male and female common frogs and observed their interactions in controlled tanks. The study found that females are far from passive during this period. Instead, they have developed several strategies to escape unwanted male attention.

Rolling: The most common tactic, used by 83 percent of the females. The female frog rolls onto her back in the pond, forcing the male to release her to avoid drowning.
Release Calls: About half of the females emitted grunts similar to the release calls made by males to signal other males to back off. The males typically make these weird sounds to keep other rivals from accidentally mounting them in the breeding frenzy. But females have apparently caught on and used the same sounds to their advantage.
Tonic Immobility: One-third of the females displayed tonic immobility, lying motionless as if dead, causing the males to abandon them.

Self-defense in mating

Tonic immobility, where females play dead, was particularly surprising to the researchers. It’s unlikely that this behavior is conscious on the female frog’s part. The researchers suspect it is an automatic stress response more common in younger, smaller frogs who are likely experiencing their first breeding season. Females not on their first rodeo are less inclined to feign death.

European female frogs are not alone in this behavior. The female moorland hawker dragonfly — common around the ponds and wetlands of Europe, Asia, and North America — also plays dead to fool males, dropping from the air and lying motionless in the ground cover to avoid costly sex after it has already mated.

The use of such advanced and intriguing strategies to avoid mating raises questions about the evolution of these behaviors and their impact on sexual selection. While it is clear that these behaviors help protect female frogs from potentially fatal mating balls, it remains unclear whether they also play a role in selecting mating partners.

More research is needed to determine if these avoidance strategies influence which males get to mate, thereby impacting the genetic makeup of future generations. Regardless, this remarkable research adds a new dimension to our understanding of amphibian behavior and highlights the complex interplay between survival and reproduction in the natural world.

The findings appeared in the Royal Society Open Science.