Grasshoppers Change Courtship Tunes to Cope With Urban Noises

Grasshoppers in urban areas are changing the tune of their courtship songs so as to be heard over the sound of traffic.

Insects like grasshoppers make calls to communicate with other members of their group for various reasons like mating, warning of predators or marking their territory.

The impact of man-made noise on insects has not been well studied until now. A team of researchers from the University of Bielefeld in Germany observed the bow-winged grasshoppers in order to understand the effect of human-made noise like traffic on their communication.

The research team, led by Ulrike Lampe from the Bielefeld University, caught 188 male bow-winged grasshoppers (Chorthippus biguttulus) from roadsides as well as quieter places. They encouraged the males to produce courtship songs by exposing them to a female grasshopper in the laboratory and recorded the songs.

Grasshoppers produce a two-phrase song by rubbing their hind legs against a protruding vein on their front wings in order to garner attention from females. The song lasts for just two seconds.

When the experts analyzed nearly 1,000 recordings, they observed that grasshoppers from the roadside produced different songs as compared to those from quieter locations. "Bow-winged grasshoppers produce songs that include low and high frequency components. We found that grasshoppers from noisy habitats boost the volume of the lower-frequency part of their song, which makes sense since road noise can mask signals in this part of the frequency spectrum," Lampe said in a statement.

Increase in noise levels has posed a major threat to grasshoppers. Human-made noise could affect courtship patterns between male and female grasshoppers. Females might not be able to hear male courtship calls or identify the males of their own species, the researchers said.

Male grasshoppers have been able to adapt to the increasing noise by changing their tune. Lampe suggests that the change is a long-term effect and "not a spontaneous behavioral adaptation to noise," a report in National Geographic said.

Researchers are further planning to study whether grasshoppers adapt to the noise as they grow during their larvae stage, or the males living on roadside habitats produce different songs due to genetic differences.

The findings of the study, "Staying tuned: grasshoppers from noisy roadside habitats produce courtship signals with elevated frequency components", are published in the journal Functional Ecology.

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