Researchers looking into the aggressive mating habits of some frogs have discovered that females frequently fake their own deaths to avoid persistent males.
This disproves the traditional idea that female frogs passively submit to the desires of their male counterparts during mating season, say the authors of the new study, which focuses specifically on the European common frog (Rana temporaria).
“Our study provides clear evidence that female frogs, even in dense mating aggregations of explosive breeders, are less helpless than generally assumed,” the researchers write in their published paper.
Explosive breeding is a pretty common strategy for frogs, which get together in large numbers for just a short period every spring to mate. As rival males simultaneously try to reproduce with individual females, they are known to form ‘mating balls’.
In a mating ball of European common frogs, it’s not uncommon for six males to surround and cling to a single female.
When there’s such a tight breeding season schedule, it seems there’s not much time for getting to know each other.
For female frogs, this schedule can be exhausting and even life-threatening. When a mating ball forms around them, females appear mostly unable to get rid of the unwanted males, and the struggle can result in them drowning.
Luckily, female European common frogs have some defenses, although these were discovered by accident.
Ecologist Carolin Dittrich and herpetologist Mark-Oliver Rödel, from the Leibniz Institute for Evolution and Biodiversity Science in Germany, were originally conducting experiments on the species to test whether males preferred a particular female body size.
The researchers placed two females of different sizes in a container of water with one male, then recorded the behavior of the frogs for an hour.
They didn’t find any size preference, but they did notice female avoidance behaviors that they decided to investigate further.
“We observed three female avoidance behaviors, namely ‘rotation’, ‘release calls’ and tonic immobility (death feigning),” the authors write.
In total, 54 females were grasped by males trying to mate. Those who displayed avoidance behaviors were often observed trying multiple techniques.
A popular technique – used by 83 percent of all clasped females – was to rotate their bodies while being clasped by the male. The team says this could be an attempt to test the strength and endurance of their slimy suitors, or it could be a way to make males more vulnerable to drowning.
Almost half, 48 percent, of female frogs resorted to release calls, a deceptive strategy that involves imitating male frog calls to trick the males into letting them go.
As many as 33 percent decided the way to avoid mating was to just play dead. Scientifically speaking, they showed tonic immobility; their outstretched limbs became stiff and they did not react to male attention.
In the end, 25 female frogs were able to get out of the males’ earnest embraces. Females with smaller body sizes were more likely to engage in escape behavior, and those that did so had greater success if they were smaller.
The study sheds new light on the reproductive strategies of the common frog and other frog species that use similar strategies.
“Tonic immobility may be a better option for a female than fighting her way out,” Dittrich and Rödel write, “as any movement in a large mating group automatically attracts attention of further nearby males and thus increases the probability of a mating ball formation.”
The authors note that their experiments might not reflect how these behaviors happen in the wild.
Finding out more about the ways of our froggy friends could help scientists with their conservation, important as many amphibian species are under threat.
For example, if female frogs are more likely to play dead in unfamiliar environments, ecologists can take steps to reduce habitat fragmentation and ensure that female frogs have access to safe and familiar breeding grounds.
Hopefully, this and further studies will help us come up with better ways to protect these curious squishy critters.
The research has been published in Royal Society Open Science.
