In a remarkable display of survival strategy, female European common frogs have been observed faking their own deaths to avoid the aggressive and sometimes fatal mating attempts of males. This behavior, scientifically known as “tonic immobility” or “thanatosis,” is a desperate measure to escape coercive encounters during the intense breeding season.
The Perils of Frog Mating
For the female European common frog (Rana temporaria), the annual breeding season can be a dangerous time. Males, often outnumbering females, will aggressively compete to mate, leading to the formation of “mating balls” where multiple males cling to a single female. These chaotic skirmishes can lead to the female being exhausted, injured, or even drowned.
A Trio of Evasive Maneuvers
To counter this, female frogs have developed a repertoire of defensive tactics. Researchers have identified three primary avoidance behaviors:
Body Rotation: The most common strategy, employed by a majority of females, involves rotating their bodies in an attempt to dislodge the grasping male. This can also serve as a test of the male’s strength and endurance.
Release Calls: Females may also emit grunts and squeaks that mimic the release calls of males. These vocalizations are typically used by a male to signal to another male that he has mistakenly grabbed him, potentially tricking the amorous male into letting go.
Tonic Immobility: When other methods fail, a female may resort to feigning death. She will become stiff, stretch out her limbs, and remain motionless. This sudden lack of response can cause the male to loosen his grip, allowing the female to escape. This behavior is observed more frequently in smaller, younger females who may be more stressed and less experienced with the rigors of mating.
Reference: Drop dead! Female mate avoidance in an explosively breeding frog
Authors: Dittrich, C., & Rödel, M.-O.
Journal: Royal Society Open Science