Disco clams are known for their dazzling display of lights, and now researchers from the University of California, Berkeley have discovered why these animals carry out these shows.
Marine biologists once believed the clams produced the lights through a form of bioluminescence, but now we know the displays are created with reflected light. However, researchers were still uncertain as to the purpose of the light show. Some investigators believed the action may have acted as a mating display, while others thought the lights might attract prey. Instead, the team of marine biologists at Berkeley found the display acts as a warning to would-be predators, advising the animals to stay away.
Researchers investigating the light shows examined different theories which sought to explain the behavior.
Ctenoides ales possesses eyes, 40 in all, that do not respond at all to the light reflected by the animals, the researchers found, eliminating the hypothesis that the displays were used for mating. Flashes became twice as frequent as normal when artificial "predators" approached, the researchers noted.
"In this case, the false predator was just a styrofoam lid. 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," Lindsey Dougherty of the University of California, Berkeley, head of the research team, said.
This provided evidence the blue lights are used to alert predators not to eat the clams. Peacock mantis shrimp were observed attempting to prey on the clams, from which they quickly recoil, acting as if the bivalve had a horrible taste.
"[Researchers] found that the clam has sulfur in its fleshy lips and tentacles and suspect that, like another clam species that drops tentacles laden with sulfuric acid to deter predators, the disco clam's sulfur also gets converted into a distasteful substance. The flashing may warn predators away, similar to the bright orange of a monarch butterfly warning birds of its toxic taste," Elizabeth Pennisi reports in Science magazine.
Researchers believe Ctenoides ales may produce a noxious chemical to ward off would-be attackers. The lights could act as an "early-warning" device to prevent attacks on the clams.
Disco clams live in submarine caves in waters off the coast of Indonesia, and adults grow to be slightly more than two inches in diameter.
Flashing in Ctenoides ales "disco" clams: behavioral function and visual cues was profiled in a meeting abstract for the Society for Integrative and Comparative Biology.
