Disco clams rely on silica nanospheres that coat the inside of their lips to create a colorful, showy, photonic display of reflected light, one that is somewhat reminiscent of a mirror ball shining multicolored light down on disco dancers. A study about how the disco clam, or Ctenoides ales, does this was published on Wednesday, June 25, in the Journal of the Royal Society Interface.
Disco clams, also known as “electric clams,” are widely dispersed throughout the Indo-Pacific region, from Australia to Indonesia. The flashy mollusks live in water anywhere from 10 to 160 feet deep. The only other animals or insects known to use silica nanoparticles to reflect light were several insects like some beetles and some butterflies. A layer of silica on the cuticles of the bodies of some beetles and the white wing scales of certain butterflies, studded by reflective beads, reflects white light.
In fact, the disco clam was also believed to use bioluminescence to create their brilliant displays, but that was before researchers who studied how they do it, like University of California at Berkeley biologist Lindsey Dougherty, discovered that the Ctenoides ales actually use nanospheres of silica that coat the soft tissues of their inner lips. She first became interested in disco clams when she was diving in Wakatobi, Indonesia.
Animals ranging from fireflies to various types of deep-sea fish like angler fish use bioluminescence to light up the night skies or deep water of the oceans. Some use the light they create to attract mates, to confuse predators, or even to lure potential prey closer to their waiting jaws.
However, the light displays that the disco clams create are solely through reflected light. The disco clams are able to synthesize silica, like can be found in sand and window glass, located just on the softer inner tissues of their mantle lips. The Ctenoides ales use these same lips for feeding. In comparison, the outer side of their lips is a dull reddish color and absorbs light rather than reflecting it.
The disco clams, which also have brilliantly-colored tendrils, create the flashing effect by rolling up and unfurling each side of their lips multiple times per second. The silica nanospheres on their inner mantle lips reflect what little available light is around, somewhat like sequins, to create a dazzling display.
According to molecular biologist Daniel Morse, of the University of California, Santa Barbara, the “rapid blinking” effect that is done “with a muscle-driven ‘shutter,'” is something that has not been seen being done by any other animal before now.
Other animals make use of so-called “photonic” parts of their bodies that act as arrays to scatter and reflect light. Examples of creatures and the parts of their bodies that have dense tissue stacked in plates which create bright colors are birds and their feathers and the wings of butterfilies. Squids also use photonics, but they can change the colors their bodies can reflect by changing the amount of spacing that exists between their plates of tissue.
In rare instances, some animals can, like the disco clams, reflect the entire visible spectrum, but when insects like beetles do it, the cuticles of their bodies appear to be white. Another example is
A few other organisms make use of silica to reflect light, but they do not reflect the full spectrum of light. Diatoms, a type of single-cell algae, have silica that composes their cell walls; but, the full visible spectrum of light is not reflected by the photonic structures in the cell walls. A type of weevil called the Pachyrhynchus argus is another example of an animal that uses arrays of silica beads to reflect light.
Lindsey Dougherty an the other researchers who worked on the study found that the disco clams have a relatively narrow band of silica nanospheres that have a diameter of close to 300 nanometers to reflect and flash their colorful light displays. Dougherty and her fellow researchers have ran calculations showing that these factors enable the disco clams to reflect the blue-green of the visible light spectrum very well. She used several techniques, such as energy dispersive x-ray spectroscopy, high speed video, computer modeling, spectrometry, and transmission electron microscopy to conduct her research.
So far, Dougherty and her team of researchers have not come up with a definitive answer as to exactly why the disco clams make use of photonics. In laboratory tests designed to imitate approaching predators, the Ctenoides ales increase the rate of their flashing lights. possibly to scare off animals that might prey on them. However, Lindsey Dougherty says that the lights that the disco clams create might also be to lure plankton to them to eat, or as a mating signal, or even as possibly a combination of all of these reasons.
Disco clams, aka Ctenoides ales, could potentially inspire engineers by their amazing ability to create colorful displays of flashing lights using silica nanospheres. Studying disco clams might eventually enable the engineers to discover new methods of manipulating light, as other animals have in the past. The Ctenoides ales are able to accomplish creating their light displays in low-light conditions, a feat that engineers might want to use to more efficiently create ambient lighting for dim or shadowy areas.
Written by: Douglas Cobb