Cricket’s call has ‘predatory roots’

CricketsImage copyright
Tony Robillard

Image caption

The researchers studied a special group of crickets with a very high frequency chirp

Scientists have discovered that the chirps of some crickets could be a cunning way to “startle” potential mates into revealing their location.

The Dartmouth College team discovered the insects’ communication system and studied females’ reactions to the males’ songs.

They say the call is likely to have evolved from males impersonating hunting bats and startling females.

The females shuddering response appears to allow males to locate a mate.

Close examination of females’ nervous systems suggested that this shudder evolved from a startle reflex, the researchers say.

The findings are published in the journal Current Biology.

Lead researcher Prof Hannah ter Hofstede investigated this unusual insect duet after a colleague presented some recordings of the insects’ particularly high frequency chirps.

“It struck me as very strange that these crickets would use such high frequencies for mating purposes,” the scientists said.

Other cricket species avoid sounds at these frequencies, which are similar to the sounds that bats make when navigating and hunting.

Escape behaviour

Prof ter Hofstede used playback experiments – playing males’ songs through speakers – to test females’ reaction to the high, bat-like chirps.

“I expected the females to walk to the speaker, because this is the usual behaviour for female crickets, but they did not do this – [they instead] made a small jerking motion after each male call,” she explained.

“From many observations of males and females together, I noticed that it was always the male walking to the female when she produced these vibrational signals.”

Further study revealed that the male calls also triggered activity in a nerve cell known to be responsible for triggering escape behaviour in crickets.

This, along with careful tracking of the cricket evolutionary tree, led Prof ter Hofstede and her colleagues to conclude that what is now a mating song and dance routine originated from a reflex startled “jump”.

This, the scientists say, is an example of “how communication systems can change over evolutionary time.

“And that even something as unlikely as a reflex response to a predator can be the origin for a new communication signal.”

Media captionVideo showing how insects’ legs allow them to be incredible acrobats (Footage courtesy of Dr Gregory Sutton and Prof Malcolm Burrows)

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