How Female Frogs Escape Male Mating Hold by Pretending to be Dead

Male frogs don't need to be gentlemanly during courtship, as long as they have a strong grip for their 'mating ball' ritual. Female European common frogs, however, have at least three tactics to evade the clutches of demanding males, according to evolutionary behavioural ecologist Carolin Dittrich and curator of herpetology Mark-Oliver Rödel from the Berlin Natural History Museum. The duo shared these strategies in an October 11 issue of Royal Society Open Science.

Rana temporaria, a type of European frog, congregate in hundreds at a single natural pool, often causing a chaotic and even dangerous scene. Females sometimes risk drowning. Males are often seen clinging onto one female, and due to external fertilization, they jostle to release their sperm onto the female's eggs in the water. Fertilization usually happens when the males keep their collective grip on the female for hours.

While researching this mating ritual, Dittrich noticed a unique defensive behaviour among the females. She observed a phenomenon in the mating tapes where the females appeared to 'play dead' and consequently make the males lose interest and leave them alone. The 'dead' females would then start moving again. Dittrich named this tactical feigning of death, 'tonic immobility'.

Proving the intentional nature of this temporary 'death' is challenging, says wildlife ecologist Brandon Güell from Florida International University in Miami. Videos of mating chaos can sometimes show female frogs going limp, which may either show exhaustion or a strategy of 'playing dead', he notes.

In Dittrich’s lab test videos, instances of male grips breaking from females who appeared to go limp were recorded. The females were also seen performing rotation, a reaction to being held that involves turning around their body's long axis. Quite like a gymnast's log roll or twirl, the goal appears to be to make the male lose their grip. Females were also seen grunting like males, often a sound made by males when accidentally held by another male during mating chaos.

This 'Let go!' female response could be common amongst many frog species partaking in this mating phenomenon, according to Güell. Despite earlier beliefs that only male frogs communicate vocally, current research points towards a greater emphasis on female communication than previously acknowledged.

Dittrich notes that female resistance of any kind has not gotten much mention in the modern literature on her frogs. She found one 20th century paper, but otherwise had to go back to the 18th century for discussion of female resistance to male power among European common frogs.

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