New research reveals asymmetry in field cricket mating calls

Gryllus_campestris_3

Just as the majority of human beings are predominantly right-handed, new research reveals that male field crickets are ‘right-winged’ when it comes to generating mating calls.

The research, published in the scientific journal Bioacoustics, examined the techniques used by male crickets to attract distant females and discovered that the sounds they make are significantly louder to the right-wing side of the insects.

The study was conducted by scientists at the University of Lincoln, UK, who accurately recorded a high-resolution, three-dimensional mapping of sound pressure levels around singing ‘Gryllus bimaculatus’ field crickets.

Dr Fernando Montealegre-Z, a leading entomologist from the University of Lincoln’s School of Life Sciences, oversaw the research. He explained: “Male field crickets generate calls to attract distant females through ‘tegminal stridulation’: the rubbing together of the overlying right wing, which bears a file of cuticular teeth, against the underlying left wing, which carries a kind of scraper or plectrum. During stridulation, specialised areas of membrane on both wings are set into oscillating vibrations to produce sound radiation.

“The location of females is unknown to the calling males so being able to increase effective signal range in all directions would maximise transmission effectiveness. However, producing an omnidirectional field of high sound pressure levels is actually problematic for the crickets, due to the mechanical asymmetry found in their sound generation systems.”

The asymmetry of the sound levels around the crickets is caused by the motion of the wings during the closing stroke phase of stridulation, when the right wing partially covers the left.

The researchers originally hypothesised that the sound field on the left-wing side of the animal would contain lower sound pressure components than on the right-wing side as a result of this coverage, and their investigations revealed this to be true.
To achieve a measure of the sound pressure produced by the crickets’ signals, the peak amplitude of each song-pulse was recorded at a number of different positions around singing crickets before being analysed. The team used a microphone mounted on a robotic arm programmed to measure the amplitudes at defined points around the animals.

Benedict Chivers, a PhD student at the University of Lincoln who led the research, said: “It is well-known that male G. bimaculatus typically produce three distinct types of acoustic signal: a long-range ‘calling song’ to females, a close range ‘courtship song’ to females, and a loud ‘aggressive song’ used in interactions with other males. Much research has examined the amplitude and frequency of these sounds, but the effect which the mechanical asymmetry in the sound generation system has on the sound field has received relatively little attention. That is why we were keen to explore this important aspect of the crickets’ behaviour.”

To read the paper in full (Distribution of sound pressure around a singing cricket: radiation pattern and asymmetry in the sound field), visit: http://bioacousticssensorybiology.weebly.com/publications.html