Tree cricket song has note of variability

Wing segments form chorus that helps shape insect?s sounds

Web edition : Monday, April 30th, 2012

Unique wings allow one type of male tree cricket to hum a different sort of tune ? one that encompasses a wide range of pitches. The discovery could mean that these males are saying a lot more than previously thought, and that potential mates might be listening for these notes.

?The frequencies might be carrying some information about the condition of the male.? An insect that is able to sing faster, and hence at a higher frequency, might actually be quite well fed, or he?s in a nice warm place you might want to be in,? says Natasha Mhatre of the University of Bristol in England. ?You now have to ask: ?What kind of information is that frequency carrying???

Crickets produce sound by rubbing their wings together. For most crickets ? including field and bush crickets ? males can produce only one musical note. Generally, the pitch of the male?s song is directly related to his size. Researchers believe that when females scout for a potential mate, they tend to be drawn to songs of deeper frequency or pitch, which are produced by larger crickets.

But certain tree crickets were known to vary their tune. Scientists had observed, for instance, that a species from southern India called Oecanthus henryi produces high-pitch sounds at warmer temperatures. Until now, it wasn?t fully understood how these critters could do this.

In the new work, scientists found that five individual segments making up a large part of this tree cricket?s wing vibrate to produce sound. That differs from most other crickets, in which only one small section of the wing is involved.

The tree cricket?s particularly long wings accommodate different types of bending ? which is associated with different frequencies. These insects can make sounds than range between 2.3 and 3.7 kHz. Using computer simulations, researchers found that smaller wings could not produce such different pitches.

Also, at higher temperatures, these crickets tended to move their wings faster to produce higher-frequency sounds, Mhatre and her colleagues report online April 30 in the Proceedings of the National Academy of Sciences.

Because the pitch of the male?s song is not tied to body size in this species, the findings raise questions about exactly what information females are gleaning when they hear these songs, says Rex Cocroft, an entomologist at the University of Missouri in Columbia.

?It?s going to change the dynamics of mate choice,? Cocroft says.

Ann Hedrick, a behavioral ecologist at the University of California, Davis, wonders what these multiple notes could mean for the Oecanthus females.

?With these tree crickets changing their frequency all over the place, it means that their females must be able to hear and respond to a broad series of frequencies,? says Hedrick. ?Also, if there are further evolutionary steps in the male song, the question is: Will the females go along with them??

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