Disco clams or known for the strobe-like light shows they create, but the purpose behind this phenomenon has been a long-standing mystery. New research suggests the clams may use these lights to scare off predators or lure in prey.
The disco clam is native to Indo-Pacific coral reefs, and their bright flashing was once believed to be the result of bioluminescence until recent research revealed a more complicated mechanism behind the phenomenon, the Society for Integrative and Comparative Biology (SICB).
Researchers used high-powered transmission electron microscopy and revealed the flashes are caused by specialized tissue that forms within the double layer, reflecting light on one side and absorbing it on the other. When this tissue is rapidly unfurled the reflecting light creates the appearance of a flashing "strobe light." These creatures are the only species of bivalve believed to have evolved this type of structural coloration.
To gain insight into the function of these light displays the researchers examined the structure of proteins in the clams' eyes, and concluded the animals' eyesight is most likely too poor to see the displays of other clams; this ruled out the idea that the lights were used as a mating technique.
In the next study the team tested the effect of the lights on predators such as octopi and snails. They created "looming" trials in which a false predator was moved in the direction of the clams to test their reactions.
"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," said lead researcher Lindsey Dougherty of the University of California, Berkeley.
The researchers also found high levels of sulphur in the clams' tentacles, and noticed predatory mantis shrimp recoiled and entered a catatonic state when struck.
In a final study the researchers introduced phytoplankton prey to the clams' tank, and observed once in the presence of a potential food source their flash rate increased significantly. This suggests the flashing lights help lure in prey, but further studies are required to confirm this.
The findings were presented at the 2015 annual conference of the Society of Integrative and Comparative Biology.
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