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Decoding Spiny Lobsters' Violin-Like Screech

John Roach
for National Geographic News
July 28, 2004
 
In the same way that a child's first week of violin lessons sends the family running for earplugs, so may the spiny lobster keep predators at bay, biologists say.

There are many species of this clawless lobster throughout the world, and they are the only animals known to make noise like an orchestra of violinists—though the lobsters' sound is much more screech than sweet music.



"It really is an intriguing mechanism," said Sheila Patek, an assistant professor at the University of California, Berkeley.

Most insects, crustaceans, and other shelled creatures make noise by rubbing a hard pick over a series of bumps or ridges, much like a person running a thumbnail across a comb or a guitarist picking at strings.

To generate their sound, the lobsters rub a soft nub—called a plectrum—found on the underside of their antennae over a smooth file located on the side of a plate below their eyes.

The noisemaking mechanism, referred to as "stick and slip," results in a screech that, according to Patek, appears to be part of the lobsters' defense strategy against predators.

Peter Bouwma, a graduate student at Florida State University in Tallahassee who is studying the spiny lobster, said that Patek's research detailing how the sound is made is "very interesting" but that scientists are uncertain as to why the lobsters make the noise.

"We know the method now, but we don't know what the function is," he said.

Lobster Defense?

Kari Lavalli is a scientist at Austin Community College in Texas and spiny lobster research collaborator with a group at Florida State University. She says spiny lobster defense mechanisms are species specific.

For example, Florida spiny lobsters (Panulirus argus), which Bouwma studies, do everything from feeding to migrating in a large group, and they employ a "collective self defense strategy when attacked," Lavalli said.

Without claws, spiny lobsters use their antennae to fend off predators. The spiny lobsters point their antennae at the approaching predators and wave them about.

"If that fails, lunging behavior accompanied by the rasping sound can occur. In a lunge, the animal does a reverse tail flip—resulting in thrusting forward rather than backward—and simultaneously whips its antennae at the predator while rasping," Lavalli said.

This group action forces the predators, such as tiggerfish, to focus on lobsters on the edge of the group. According to Bouwma, the Florida spiny lobsters are otherwise quiet during interactions with tiggerfish.

Other lobsters, such as the coral-reef-dwelling spotted spiny lobsters (Panulirus guttatus) are solitary animals. And their defensive strategies are less well understood, Lavalli said.

In 2003 Bouwma surgically removed the plectrum off some Florida spiny lobsters to determine whether predators had a preference between lobsters that could and could not make noise.

He found that the fish did not have a preference but noted that the fish he used were "experienced"—that is, they had previously been exposed to lobsters and thus were perhaps not fazed by the rasping noise.

Currently, Bouwma is repeating the experiment with fish that are encountering lobsters for their first time—a condition that may be more representative of the natural world. "So far, there is a difference from what I saw last summer," he said.

Bouwma hopes to present his results next year.

Soft-Shelled Protection?

The spiny lobster's ability to make noise rubbing one soft body part across another is particularly handy for growing lobsters, which periodically shed their outer, hard skeletons to make room for new body tissue.

The shedding, known as molting, happens periodically depending on a host of factors. The factors range from food availability to the presence of other lobsters, according to Patek.

Shedding leaves the molting lobster vulnerable, with a softened outer shell for a few days.

One possibility is that the lobsters originally evolved this rasping ability for protection when they molt. Or perhaps the stick-and-slip mechanism was simply an accident of evolutionary history. More scientific evidence is needed to understand the evolution of this system, according to Patek and Bouwma.

Patek said: "They will make the antipredator sound—the rasp—when interacting with predators, regardless of whether they are molting or not. They also make other kinds of sounds, using other anatomy. We're still trying to figure out the functions of those sounds."

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