An unsuspecting shellfish with an adorable-looking shell may contain the secrets of fast internet speed.
Heart cockles (Corculum cardissa) have special windows in their shells that let light inside via fiber-optic crystal structures, according to a new paper in the journal Nature Communications.
This quirk of evolution marks the first time fiber-optic cable bundles have been spotted in a living organism, and it could inspire cheaper methods for manufacturing internet fiber-optic cables.
"The heart cockles' fiber optic cables and microlenses may inspire optical technologies," the researchers wrote in the paper.
Like many mollusks, these heart cockles—which resemble clams—have a symbiotic relationship with algae that live inside their shells. In these relationships, the algae gain access to light and food while living inside the animal's shell. In return, the mollusk eats the algae.
Other species of mollusk that have this type of symbiotic relationship open their shells to let the light in, allowing the algae to photosynthesize. However, heart cockles stay shut. This is because their shells are made of aragonite—a crystalline form of calcium carbonate—and they have special tiny windows in these shells that transmit light along optical fibers made of the mineral. This allows the light to penetrate the shell without it having to open.
The fiber-optic windows allow twice as much light to pass through than they would if they were holes. These windows also filter out ultraviolet wavelengths from the light entering the shell that would kill the algae within.
"Heart cockles transmit 11–62 percent of photosynthetically active radiation but only 5–28 percent of potentially harmful UV radiation to their symbionts. Beneath each window, microlenses condense light to penetrate more deeply into the symbiont-rich tissue," the researchers wrote.
The fiber-optic cables we use for the internet are made of thin strands of glass or plastic, each about the diameter of a human hair, which are bundled together in cables. Each fiber strand has a core (where light travels) surrounded by a cladding that reflects light back into the core, preventing signal loss.
The aragonite in the shells forms the window thanks to an organic matrix that controls the shell growth, forming the mineral into long, fibrous crystals. At the window, these crystals are bundled together into a section of fiber-optic cables that focus light, while throughout the rest of the shell, the aragonite is crisscrossed and opaque.
"Within each window, aragonite forms narrow fibrous prisms perpendicular to the surface. These bundled 'fiber optic cables' project images through the shell," the researchers wrote. "Heart cockles have evolved transparent windows in their shells with what is, to our knowledge, the first example of bundled fiber optic cables in a living creature."
The researchers said the aragonite fibers strongly resembled human-made fiber-optic cables, except without the cladding. This suggests that these natural fibers could inspire cheaper and more efficient ways to make fiber-optic cables for human use.
This isn't the first time humans have stolen technology from the natural world.
The researchers wrote, "Previously, the glass spicules of sponges inspired lightweight mechanical architectures, while microlenses in peacock spiders inspired antireflective polymer microarrays."
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References
McCoy, D. E., Burns, D. H., Klopfer, E., Herndon, L. K., Ogunlade, B., Dionne, J. A., & Johnsen, S. (2024). Heart cockle shells transmit sunlight to photosymbiotic algae using bundled fiber optic cables and condensing lenses. Nature Communications, 15(1). https://doi.org/10.1038/s41467-024-53110-x
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