A new study found that female European common frogs have developed avoidance behaviors to ward off aggressive male breeding tactics.
Female European common frogs may fake their own deaths to avoid mating with male frogs, a recent study found.
The frogs (Rana temporaria) are “explosive breeders,” meaning their mating season is very short. Within a two-week period each spring, the male frogs compete with each other to mate with as many females as possible. Since they typically outnumber the females by a large margin, multiple males will often try to mount the same potential partner at once, forming what is known as a “mating ball.”
This behavior can be dangerous for the female frogs, as it may cause them to drown or crush them to death.
Until recently, scientists believed the female frogs were passive during this breeding season. But according to the new study, published in the journal Royal Society Open Science, researchers discovered that this is not the case.
“Rather than being passive and helpless, we find that 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,” said Carolin Dittrich, co-author of the study and a researcher at the Natural History Museum in Berlin, in an interview with Live Science.
Researchers collected male and female common frogs during their breeding season and divided them into tanks to observe their behavior. They found the female frogs used three strategies to escape the grasp of the male: rolling, release calls, and tonic immobility.
The most common strategy was rolling, in which the female rolls onto her back while the male is on top of her. The study found that 83 percent of females that were mounted by a male performed this evasive maneuver.
“This puts the male underwater, so the male lets go to avoid drowning,” Dittrich said.
The second most common response was emitting grunts that mimic the “release calls” that male frogs make to keep other males from unintentionally mounting them during the chaos of the breeding season. Nearly half of the females used this tactic to avoid sex.
Most surprisingly to the scientists, one-third of the female frogs appeared to play dead when a male attempted to mount them. They lay motionless with their limbs outstretched in a display of tonic immobility.
“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 response to stress.”
The study found that smaller, younger frogs were more likely to play dead than larger, older frogs. Dittrich said this is possibly because younger females are more likely to become stressed since they haven’t lived through as many breeding seasons, leading them to react more strongly.
“This immobility can last several minutes,” said Dittrich in an interview with Newsweek. “In one of our videos we see that a male is dragging an immobile female until he lets her go. She stays in that immobile position for a couple of minutes until she turns and swims away.”
Overall, 46 percent of female frogs who were mounted by a male successfully escaped their grasp.
Faking death is most commonly used to avoid predators in species other than the European common frog. Utilizing it as a strategy to escape breeding has only been seen in a few other species, including dragonflies, some spiders, and sharp-ribbed newts.
It is also unclear if the avoidance behaviors are related to sexual selection in any way or if they are solely for protection. It could be that female common frogs avoid mating with certain male frogs to “choose” their partner, although Dittrich believes it is more likely that it is to protect the female from the deadly mating balls.
“We cannot say that they choose a particular male, as choice would imply that they benefit from choice,” Dittrich said. “We can only say that females show avoidance behavior, but not whether this behavior is targeted by sexual selection.”
After learning about these frogs that play dead to avoid sex, discover how two female mice reproduced without a male partner. Or, learn about the frogs near Chernobyl that have changed colors to adapt to the radiation.