In the wild world of nature, where a living thing's only purpose is to successfully pass on its genes at all costs, it's not surprising that many species engage in aggressive and even lethal mating behaviors. Researchers led by Carolin Dittritch of the Konrad Lorenz Institute for Selective Breeding in Vienna discovered by chance that female frogs fake their own deaths to avoid mating with unwanted males.
This undermines assumptions that the clustering of male frogs that often occurs during such free-breeding frenzy is beyond the control of helpless female frogs.
This tonic immobility behavior, or "thomatosis," is an adaptive deception that prey species use when encountering a predator. Recently, scientists were surprised to find that Polyrhachisfemorata ants in the entire ant colony began to "play dead" on Kangaroo Island, Australia. This is the first time that this collective "playing dead" behavior has been discovered. However, this phenomenon has only been observed a few times during intraspecific sexual behavior.
During intense, intense, frenetic group matings known as "explosive breeding" (a term that leaves little to the imagination), male frogs typically harass, intimidate, and physically overpower female frogs in the water, which can result in the death of one or both frogs.
However, the female frog has devised a cunning strategy to avoid harassment by her unwanted mate by convincing her pesky suitor that she is dead. After all, a dead female animal would not allow a male animal to waste its energy on continuing the family line. This mating-related tonic immobility behavior has only been observed in one amphibian species, the Pleurodeles waltl.
"We observed three female avoidance behaviors, namely 'rotation', 'release call' and tonic immobility," the researchers noted. "We defined 'rotation' as the female starting to rotate around her body axis when held by the male, while the male attempted to counteract the rotation with his hind feet."
Scientists observed two calls produced by female frogs - grunts and squeaks - and in some 33 percent of the animals, scientists saw the frog play its life's role, stiffening its limbs and playing dead, sending a convincing message of fatal disobedience to its hapless mate. Since both the production of sperm and the act of mating itself require a lot of energy, this Oscar-worthy act is enough to deprive it of its usual undivided attention. (After all, there are many four-legged toads in the pond).
Although the majority of female frogs observed (83%) used the "tail flick" technique, in which they rotate their bodies while being held tightly by a male in the water, both to test the suitor's strength and avoid suffocation, this strategy has been quite successful.
At the same time, scientists aren't entirely sure why female frogs have adapted this behavior; male frogs don't provide parental care or help defend resources, so selectivity has little benefit for the frog. As for the "test of strength" argument, larger male frogs have no higher mating success rates than smaller frogs.
This behavior is particularly strange because a more common adaptation is physiological evolution to counter aggressive mating by males. For example, many waterfowl have traits that co-evolved to ward off males who have selectively evolved more efficient reproductive organs. These features include dead-end "pockets" in the reproductive tract that filter out undesirable mates' sperm, and elaborate spiral patterns that counter the spiral pattern of the male's penis.
Although the frog's tactics are not foolproof, with only a 46% escape rate for frogs firmly grasped by male frogs, it can be said that pretending to be dead is faster than evolution.
The research was published in the journal Royal Society Open Science.