The disco clam, so named because light flashes from its mirrored "lips," turns out to be the disco ball from hell. New research has found that the clam's impressive light show attracts prey, which may be rendered immobile by noxious, acidic mucus produced by the busy bivalve.
The unusual findings, reported at the 2015 annual conference of the Society of Integrative and Comparative Biology in West Palm Beach, Fla., solve the mystery as to why the disco clam (Ctenoides ales) puts on such a flashy light show.
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At first it was thought that the clam might be trying to woo mates, but that sentiment might have been felt more by researcher Lindsey Dougherty of UC Berkeley. She was thrilled when she first encountered the unique clams in a dark, underwater cave during a dive in Indonesia.
"It was on that trip I first saw the disco clam, and immediately fell in love," reminisced Dougherty in a press release.
She and her collaborators, Professor Roy Caldwell and undergraduate Alexandria Neibergall, brought some of the clams back to a lab to investigate why and how the clam's flash.
First, the researchers determined that the flashes are caused by specialized tissues that form a double layer that is reflective to light on one side, but absorbent on the other.
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When the tissue along the lip margins of the clam's mantle is rapidly rolled and unfurled, the reflecting light gives the appearance of flashing. These tissues are so reflective that they can even flash using the low levels of blue light found in the caves. Disco clams are the only species of bivalve to have evolved structural coloration of this kind, according to the researchers.
The team next examined the structure and proteins in the clam's tiny eyes using a powerful microscope. The researchers concluded the clam's vision is too poor to allow it to observe displays by other clams. Since the clams aren't visually attracted to each other, the wooing theory around the light show was tossed out.
The scientists then investigated what would happen if a predator threatened the disco clam.
"In this case, the false predator was just a styrofoam lid," Dougherty said. "But it turns out a styrofoam lid is indeed pretty scary to the clams, because their flash rate almost doubled from just under 2 Hz to just under 4 Hz."
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Intriguingly, the researchers found high levels of sulfur in the clam's tentacles. When a peacock mantis shrimp tried to attack the disco clam, it recoiled and entered into a catatonic state. The researchers believe that the clam is releasing toxic mucus to repel predators.
When phytoplankton - a tasty treat for certain clams - was introduced into the disco clam's tank, the clam flashed like crazy. Phytoplankton is attracted to light, so this strongly suggests that the flashy light show helps to draw in prey.
Here's a video showing what the disco clam's light show looks like, with appropriate added musical accompaniment: