“Our observations show that females in explosive breeding frogs may not be as passive and helpless as previously thought,” said a study published Wednesday in the Royal Society journal.
According to the study, one of the methods female European common frogs use to avoid potentially deadly explosive mating situations is feigning death. Smaller female frogs were more successful at escaping mating.
Researchers explained that male and female frogs have different reproductive strategies that can result in sexual conflict. Male reproductive strategies can include harassment, forced copulation and intimidation, which negatively affect female survival and thus lead to reproductive failure for both.
In “explosive” mating events, “several males cling to a female, which are mostly unable to get rid of the unwanted males,” and they can die. Previous literature indicated that females had no means to reject unwanted males during explosive breeding situations.
However, researchers found that the European common frogs have at least three methods of avoiding mating. They were observed rotating their bodies and grunting or squeaking out “release calls” in addition to playing dead.
That last method was the most surprising.
“Tonic immobility as a tactic to avoid mating or male harassment has only been observed in a handful of species and only in one other amphibian,” said the study.
Often, this behavior is seen in spiders and dragonflies. In Frogs, researchers said it might be tied to stress and corticosterone levels.
“An important source of stress, that could trigger tonic immobility, is the frequently observed formation of ‘mating balls’, which often result in the death of females and males by drowning,” said the study. Staying still might be safer than fighting, as that would increase motion that could potentially attract more frogs to the mating ball.
Around 33% of females used the tactic, compared with 48% who resorted to release calls and 83% who attempted rotating. Often, the frogs that played dead used it in combination with rotating and calling. Overall, 48% of the females were able to escape mating.
“Future studies should consider investigating different frog densities, sex ratios and age classes, to test for mate choice and the potential costs associated with reproduction,” said the researchers. “However, our study provides clear evidence that female frogs, even in dense mating aggregations of explosive breeders, are less helpless than generally assumed.”
Frogs included in the study are from Europe. Southeastern states such as Louisiana are known to be the “heart” of frog and toad diversity in the U.S., according to the University of Georgia Press.