Image: DUKE UNIVERSITY NEWS SERVICE |
Lobsters startle their predators by playing the biological equivalent of a violin, a graduate student from Duke University has discovered. When attacked, some species of spiny lobsters of the Palinuridae family produce a loud rasping noise similar to a cricket's chirp. But in an article published today in Nature, Sheila Patek shows that they don't make the sound in the same way. Whereas crickets and other animals produce sound by scraping hard "picks" over ridged external skeletons¿much as you might play a washboard with a file¿spiny lobsters make noise by rubbing soft surfaces together, like drawing a bow over a violin¿s string.
Patek found that the lobster's "bow" is made up of a tiny velvet-like extensions on its antennae, called plectrum. Using underwater microphones, motion sensors and high-speed videos, she observed that lobsters produce their typical noise by rubbing the plectrum against the equivalent of a string¿a smooth plate tissue covered with microscopic ridges located just below the eye. Friction between these two surfaces makes them stick and slip many times each second. Although the resulting sound is far from musical, the mechanism is basically the same one used to play many string instruments.
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Spiny lobsters' armoured shells and antennae are usually enough of deterrent for most of their enemies. As Patek points out, however, the sound-based defense can become a vital strategy for lobsters during molting, when their shell is softened and they are most vulnerable to predators. In this case, the string-and-bow mechanism allows them to make sounds without relying on hard parts. "It is a pretty clever solution," Patek says, "and it is the first time that it is shown in animals."