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 flipresulting in thrusting forward rather than backwardand 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 timea 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.
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 soundthe raspwhen 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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