15 Nov 2012

Grasshopper love affected by background noise levels

12:57 pm on 15 November 2012

A study in Germany has found grasshoppers that live in noisy urban environments are having to change their tune to find love. High levels of background noise may affect their mating process.

Researchers from the University of Bielefeld say the insects are forced to increase the volume of the low-frequency sections of their call.

The BBC reports the team caught 188 male bow-winged grasshoppers from noisy roadsides and quiet rural locations.

Lead researcher Ulrike Lampe, a PhD student at the university's department of evolutionary biology, told the BBC:

"Bow-winged grasshoppers are a good model organism to study sexual selection because females can respond to male courtship songs with their own low-frequency acoustic signal, if they are attracted to a male song," she said.

The grasshoppers produce their mating call by rubbing a toothed file on their hind-legs against a protruding vein that is located on their front wings.

The male's song consists of short phrases of two to three seconds that increase in amplitude towards the end.

The first part of the call comprises slower ticking sounds that increase in speed and amplitude, leading to a buzzing sound towards the end of the phrase.

Results recorded in lab

In order to stimulate the males to begin mating calls, scientists exposed the males to a female and recorded the results in the laboratory.

The BBC reports the team then analysed the differences between the results of each group of grasshoppers.

Results showed that compared to males from rural locations, urban grasshoppers "shift the frequency peak of the lower part of their spectrum upwards," Ms Lampe explained.

This would make sense to avoid low-frequency noise, as traffic noise could mask signals in that part of the frequency spectrum.

The team's findings demonstrate that traffic noise could be upsetting the grasshopper's mating system.

Results of the study are published in the Functional Ecology journal.