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Female Frogs Play Dead To Get Rid of Males

A frog lurking in a plant pot.
Credit: Ladd Greene / Unsplash.
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Well-studied species can still hold “big surprises”

When mating season comes around, male frogs are known to demonstrate some rather questionable behaviors towards the opposite sex. This includes the formation of a “mating ball”, where several male frogs cling to a single female – often killing her in the process.

A new study published in The Royal Society Open Science journal suggests that female frogs have developed a number of defense strategies to protect themselves against the wrath of eager-to-breed males.

“We describe female mate avoidance behaviors in the European common frog,” Dr. Carolin Dittrich and Mark-Oliver Rödel from the Museum für Naturkunde – the authors of the study –  write.

In spring 2019, Dittrich and Rödel collected male and female common frogs, placed them in a water tank where they could move freely and recorded their behaviors using a webcam. “We observed three female avoidance behaviors, namely ‘rotation’, ‘release call(s)’ and tonic immobility (death feigning). These behaviors were significantly associated with smaller female body size, and smaller females were more successful in escaping amplexus.”

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Rotation is when a female frog turns around her axis. The release call observed by the researchers takes two forms: a deeper lowfrequency “grunt”-like sound that resembles the male’s release call, and a higher frequency squeak. The third behavior described is, in the researchers’ opinion, the most “astonishing”: death feigning, simply put, means the frogs are “playing dead”. Yes, that’s right; to protect themselves against swarms of sexually aroused male frogs, the female frogs stiffly extend their arms and legs away from the body, keeping incredibly still until the male releases them from its grasp.

"Tonic immobility in the context of mating is exceptional and very rarely observed. I know of only a few studies that have found tonic immobility associated with mating, for example in spiders or dragonflies. It is generally assumed that this strategy is used as a last resort to avoid predation," says Dittrich.

"We therefore suspect that this defensive behavior has evolved to protect the female from the formation of ‘mating balls’, which can often lead to the death of the female. Calling allows females to show that they are not ready to mate, and if this is of no use, stressed females can fall into tonic immobility,” Rödel describes.

Dittrich adds, "Our study shows impressively that even very common and well-studied native species can still hold big surprises.”

Reference: Dittrich C, Rödel MO. Drop dead! Female mate avoidance in an explosively breeding frog. R Soc Open Sci. 2023;10(10):230742. doi: 10.1098/rsos.230742