Grasshoppers Near Highways Change Their Mating Calls

On any given day, traffic victimizes many individuals living in urban areas.

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Everybody hates traffic jams. But while humans are stuck sitting at their steering wheels, futilely honking, checking the time and muttering along with talk radio, another species has found a way to evade the inconveniences of vehicular congestion.

A study published Nov. 14 in the journal Functional Ecology found that male bow-winged grasshoppers, Chorthippus biguttulus, who live near highways adapt their mating calls to make them audible to females over expressway noise. This exploration was one of the first of its kind in insects, although studies have examined the effects of human noise on other animals including as birds and frogs.

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“To date, research has mainly focused on the effects of urban or anthropogenic noise on acoustic communication in vertebrates, whereas not much is known about potential effects on communication in natural populations of invertebrates,” the study’s authors, from the University of Bielefeld in Germany, wrote in the paper.

In 2010 the scientists captured 188 male grasshoppers during the July-September mating season including samples from nearby populations — some of which were situated next to a main highway while others lived in a quieter habitat.

They induced the males to perform their calls — which grasshoppers produce by rubbing a toothed file against a vein on their front wings — by positioning them in an illuminated box on a platform inside a dark room, mimicking their favorite conditions for singing in nature. (Each of the singing males also faced one female grasshopper from his own population during his performance.)

The scientists analyzed the recordings and discovered that even in the laboratory environment, calls by grasshoppers from highway-adjacent habitats included tones of higher frequency than those of insects residing in quiet environments. These findings support the idea that the bugs alter their tunes to prevent the traffic noise from drowning them out.

“This result suggests that grasshoppers use higher frequencies in the presence of elevated background noise levels to avoid signal degradation or masking, representing the first evidence that anthropogenic noise affects acoustic communication signals in natural insect populations,” the researchers wrote.

The scientists also remarked that this change in courting songs could affect the mating process, including by making males less attractive to females.

“Increased noise levels could affect grasshopper courtship in several ways,” Ulrike Lampe, one of the study’s authors, told the BBC. “It could prevent females from hearing male courtship songs properly, prevent females from recognizing males of their own species, or impair females’ ability to estimate how attractive a male is from his song.”

Humans may hate traffic, but at least that’s one thing we don’t have to worry about.

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