Cuttlefish Flirt with Polarized Light Patterns Invisible to Human Eye
A groundbreaking study has revealed that cuttlefish, marine creatures related to squids and octopuses, engage in a unique form of courtship by displaying patterns on their skin that are based on the orientation of light waves. These patterns, which are completely invisible to the human eye, serve as a sophisticated mating signal to attract potential partners.
Decades of Scientific Discovery
For over 30 years, researchers have known that cuttlefish possess the ability to see the orientation of light waves, a capability known as polarization vision. Additionally, parts of their bodies can reflect polarized light. However, the recent study, published in the Proceedings of the National Academy of Sciences, provides the first concrete evidence that cuttlefish actively use this ability in their mating rituals.
The research was led by Arata Nakayama, a research fellow at the National Taiwan Normal University, who conducted his doctoral work at the University of Tokyo. Nakayama spent more than a month observing cuttlefish in a tank at the Asamushi Aquarium, patiently waiting to capture their courtship displays on camera.
The Hidden Patterns of Courtship
During courtship, male cuttlefish extend a specialized pair of extra-long arms in front of them. To the naked human eye, these arms appear with dark and light stripes. However, using a polarized-sensor camera, Nakayama discovered a hidden pattern: a combination of vertically and horizontally polarized light oscillating in specific orientations.
"When I saw the polarization pattern on my laptop, I was incredibly excited and also confused, because it didn't look like any polarization pattern previously reported in animals," Nakayama recalled. "That was honestly one of the most unforgettable moments in my life."
Further analysis revealed how cuttlefish produce this effect. During the display, the male shrinks pigment cells in its arm skin, exposing reflective cells beneath. These cells polarize light horizontally, but from the female's perspective—typically positioned a few inches below—some of this light passes through transparent muscles, rotating its orientation to vertical.
Evolutionary and Practical Implications
Since this polarization pattern is observed only in males during courtship, it likely evolved as an eye-catching mating display. Roger Hanlon, a senior scientist at the Marine Biological Laboratory in Woods Hole, Massachusetts, who was not involved in the study, praised the findings.
"This is just opening the door to a very novel, very different way to manipulate light for an animal signal," Hanlon said. He added that the research could inspire bio-inspired engineering, leading to new materials with potential military applications, such as underwater signaling for ships and submarines.
For Nakayama, the study highlights how animals' sensory capabilities and communication methods work in tandem. "Different species have different ways of standing out, and studying those differences helps us understand evolution itself," he explained.
A Broader Perspective on Animal Communication
This discovery adds to the growing body of knowledge about animal adornments used in mating. While some, like a peacock's tail feathers, are visible to humans, others rely on sensory abilities we lack. Polarized light vision is common in many animals, including some fish and insects, but its use in cuttlefish courtship is a remarkable example of evolutionary adaptation.
The study underscores the complexity of marine life and the innovative ways creatures communicate in their environments. As research continues, it may uncover more hidden patterns and signals in the animal kingdom, deepening our understanding of nature's diversity.
