A new study from the University of Zurich , published in the journal Ecology has shown that the moorland hawker dragonfly pretends to drop dead to escape aggressive males. There are a few instances of other animals faking their own deaths to avoid being killed but this might be the only study of female animals faking deaths to avoid mating.

Researcher Rassin Khelifa was collecting insect eggs in the Swiss Alps when he noticed that a female dragonfly would fake her own death by falling from the sky and then lie motionless on the ground until the male dragonfly leaves the area.

"While I was waiting at a pond near Arosa, at about 2,000 meter elevation," he wrote, "I witnessed a dragonfly dive to the ground while being pursued by another dragonfly... the individual that crashed was a female, and that she was lying motionless and upside down on the ground. Upside down is an atypical posture for a dragonfly. The male hovered above the female for a couple seconds and then left. I expected that the female could be unconscious or even dead after her crash landing, but she surprised me by flying away quickly as I approached. The question arose: Did she just trick that male? Did she fake death to avoid male harassment? If so, this would be the first record of sexual death feigning in odonates."

After making this observation, Khelifa spent the next few months documenting instances where a female dragonfly would crash land and play dead while being pursued by a male dragonfly. He observed that when female dragonflies arrived at the pond where male dragonflies were "constantly patrolling looking for a mate", the females would be be intercepted mid-air. After copulating nearby, the male dragonfly would fly away, leaving the female unprotected while she laid her eggs.

In 86 percent of cases that Khelifa observed, the females would crash to the ground and fake their deaths. "Those that kept flying were all intercepted by a male but if they were motionless, 77.7 percent of the dragonflies were successful in deceiving the coercive male," he wrote.

This behavior could have resulted from exaptation, a term in evolutionary biology to describe a trait that has been co-opted for a use other than the one for which natural selection has built it. "Since death feigning already exists in the behavioral repertoire of dragonflies, females of the moorland hawker expanded the use of this anti-predatory function to avoid male coercion," Khelifa wrote. "On the other hand, the origin of this exaptation is probably sexual conflict where each sex adopts reproductive strategies that best serve its own survival and reproductive success."

Plummeting to their fake deaths appears to help female dragonflies survive longer and produce more offspring by avoiding coercion. "Sexual death feigning is one of the rarest behaviors in nature, and due to its scarcity, it has received little attention in behavioral ecology. Currently, it is restricted only to arthropods. It would be interesting to know whether this scarcity is true or just an artifact related to the lack of behavioral investigations or difficulty in detecting this behavior."

Published on: Apr 29, 2017
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