The first time Lindsey Dougherty saw the shimmery, lightning lips of the Ctenoides ales file clam, she was diving in Indonesia with her sister. When she surfaced, she remembers saying, “I’m going to do a Ph.D on this! I’m in love!” Dougherty, now at the University of California, Berkeley, is about 2 years away from her goal. But in the meantime she has added a lot of scientific understanding to the understudied mollusk.
New research published today in the Journal of the Royal Society Interface confirms that C. ales, also known as the disco clam, is one of the few creatures that use silica micro-structures to reflect light. The clam does it so well that for years divers and scientists alike believed that it was generating its electric display with light-producing chemical reactions known as bioluminescence.
Dougherty first shattered that idea last year with a series of presentations showing that the lips were lined with reflective silica spheres. For the new study, Daugherty and her colleagues used an electron microscope to look at the spectral signature of the structure of the clam’s lip tissue. On one side were those microscopic balls of silica—the primary element in glass and quartz. The other side was dark, and only reflected light on the red-end of the visible light spectrum. Because red light doesn’t transmit well underwater, the dark side of the clams’ lips is effectively non-reflective.
Conversely, the silica-side reflects 85 to 90 percent of all white light when underwater. “They’re almost ideal reflectors in blue-green water environments,” said Dougherty. The team confirmed this by using computer models to see how the spheres’ structures reflected light at four different wavelengths.
Using a high-speed camera, they were able to see exactly how the clams make the flash: By rapidly rolling and unrolling their lips, exposing the dark and reflective sides at a rate of about 2 times per second.
Divers can find disco clams all the way from Australia to Indonesia in water from 10 to 160 feet deep. Even in shallow waters, the clams tend to squirrel themselves away into relatively dark nooks, which explains why it seemed so natural to think that their display was bioluminescent.
From an evolutionary perspective, lightning lips are a pretty costly adaptation: They need special muscles to control the furling motion, and silica is a rare element in the ocean. Dougherty says there are three possibilities: The lips are to lure in mates, attract prey, or ward off predators.
Moving forward, she’s going to be researching the clams’ eyes (they have up to 40). Knowing how the clams see could unlock the secret behind their most prominent feature.
This might satisfy her (and our) scientific curiosity, but the things she’s already discovered might be more useful in a practical sense. Dougherty points out that tech companies like Qualcomm have used research on butterfly wing iridescence to make screens that don’t lose their brilliance in sunlight. She thinks the clam’s low-light reflectance might be able to do something similar for using tech in dim settings. Actually, she hopes her research catches the company’s eye, “Because who knows, maybe will offer me a huge grant.”
Get down to this awesome video of disco clams from UC Berkeley: