Every creature on this planet that reproduces sexually possesses its own distinct method for attracting a mate, but cuttlefish are capable of something truly extraordinary. The findings of a novel investigation have been documented in the journal Proceedings of the National Academy of Sciences.
Male Andrea cuttlefish (Doratosepion andreanum)—rather unremarkable to the human eye—employ their birefringent tentacles to literally warp light, generating a highly conspicuous signal precisely tuned to cuttlefish vision.
We were already aware that the remarkably unusual eyes of cuttlefish can discern the orientation of light waves, known as polarization. This new discovery demonstrates they advance even further, actively manipulating polarization to convey information in a specific manner.
“Our results,” state the research team led by aquatic biologist Arata Nakayama from the University of Tokyo, “underscore the substantial role of light polarization in animal communication and reveal that polarization signals—much like vibrant sexual ornamentation—can achieve high visibility through fundamentally different optical mechanisms.”
The communication repertoire of cuttlefish is astonishingly intricate, encompassing both mesmerizing shifts in color and patterns, alongside the execution of complex maneuvers using their pliable appendages.
They also possess peculiar eyes, unlike those of other animals, featuring unique W-shaped pupils. Despite the common belief that they are colorblind, they can perceive aspects of visible light inaccessible to humans—specifically, the polarization of its transverse waves.
As light propagates, it generally vibrates in numerous directions simultaneously, yet its movement can be constrained to a single orientation—a property known as polarization. Polarizing sunglasses function by blocking light vibrating in specific planes, allowing only light oriented a certain way to pass through the lenses.
Reflection from certain surfaces or passage through translucent or transparent media can also direct these oscillations into alignment, thereby polarizing the light.
Ever since scientists uncovered the capacity of cuttlefish to perceive light polarization, they suspected this light property might be part of their communication toolkit. A 2004 study not only established that cuttlefish body tissues polarized light but also presented limited evidence suggesting the animals responded to this signal.
Nakayama and his associates developed a more rigorous study to ascertain this, capturing footage of the courtship displays of male Andrea cuttlefish.
These cephalopods feature two very lengthy, sexually dimorphic limbs that are extended straight forward while coiling during female courtship, concurrently with iridescent bands of color appearing across their bodies.
The researchers collected wild cuttlefish and situated male-female pairs in observation tanks under tightly managed lighting conditions designed to mimic the horizontal light polarization present in the ocean. They also recorded every encounter using polarization cameras, while capturing images of the cuttlefish when they were not courting as a baseline.
The videos revealed that when a cuttlefish twists its tentacles in a particular way, horizontally polarized light passes through a translucent muscle. This tissue also exhibits birefringence, rotating the light’s polarization by nearly 90 degrees into a vertical orientation.
This process results in alternating bands of horizontally and vertically polarized light—a maximum contrast for the cuttlefish eye, a signal uniquely tuned to capture attention. It is akin to a bold serenade conducted through light.
What is particularly fascinating is that the cylindrical geometry of the limb enhances this contrast, presenting the perfect shape for converting a horizontal light ray into a vertical one.
In a resting state, the cuttlefish did not generate the polarization signal. This implies that these animals have evolved an ideal biological wave apparatus specifically engineered to aid their reproductive efforts.
The question of whether cuttlefish utilize polarization signals beyond courtship remains open—a query answerable only when scientists gain a better comprehension of their concealed visual world.
“Just as is the case with the widely known and heavily studied diversity of animal coloration, there may exist an analogous diversity of polarization signals in polarization-sensitive animals—signals that remain entirely unknown to us because they are invisible to the human eye,” the researchers write. “This investigation sheds light on a portion of this hidden diversity.”
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