November 14, 2012
Grasshoppers Alter Their Courtship Song Around Traffic Noise
Brett Smith for redOrbit.com - Your Universe Online
Males looking to find a mate are always trying to stand out, from peacocks´ colorful plumage to the slightly fictitious profiles on Match.com.According to a newly published report in the journal Functional Ecology, scientists at the University of Bielefeld in Germany have found that male grasshoppers also try to stand out by altering their mating song when surrounded by a noisy urban environment.
"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,” said study co-author Ulrike Lampe, from the university´s Department of Evolutionary Biology.
While the effects of artificial noise on animal communication have been studied in the past, previous research has focused on vertebrates alone.
"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,” Lampe said.
The bow-winged grasshopper (Chorthippus biguttulus) is a widespread species across Central Europe, with adults establishing their presence between July and September in the region´s grasslands. The average grasshopper is about 0.6 inches long and they can vary in color from green to red or purple.
Lampe and her colleagues caught 188 male bow-winged grasshoppers, half of which were taken from quiet locations and the other half from beside busy roads. The team then studied the two groups' courtship songs in the laboratory after exposing them to a female grasshopper.
The grasshoppers produced their song by running a toothed file on their hind legs along their front wings, causing them to vibrate. The typical song consists of two short phrases, two or three seconds long that increase in amplitude towards the end. The insect begins the phrase with slower ticking sounds that gradually increase in speed and amplitude, becoming a buzzing sound towards the end of the phrase.
After analyzing almost 1,000 recordings of their grasshoppers, the German research team found that grasshoppers that had lived beside noisy roads produced different songs than their more rural counterparts. The grasshoppers from noisy environments had boosted the levels of their songs in the 6 to 9 kHZ range that coincides with low-frequency road noise that could disrupt their songs.
"Increased noise levels could affect grasshopper courtship in several ways,” Lampe said. “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.”
In their report, the scientists said that future studies could work to determine if the difference in songs is due to “a more permanent mechanism for signal adjustment” or a change in behavior, “which was found in different bird species adjusting to high background noise levels.”
Those more permanent mechanisms include determining if the grasshoppers begin to adapt to noise during their larval stage and if genetic differences play a role in the adaptation.