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Researchers have discovered the mechanisms behind electric blue spots on blue-spotted ribbontail rays by identifying nanostructures that reflect light and create bright colors. The discovery has implications for
Researchers have discovered the mechanisms behind electric blue spots on blue-spotted ribbontail rays by identifying nanostructures that reflect light and create bright colors. The discovery has implications for the development of chemical-free coloration technologies as research continues into similar phenomena in other marine species.
Scientists have identified the unique nanostructures responsible for the electric blue dots of the blue-spotted ribbon tail (Taeniura lima), with possible use to create chemical-free coloration. The team is also conducting ongoing research into the equally mysterious blue coloration of the blue shark (Prionace glauca).
Skin color plays an important role in how organisms communicate, providing vital visual cues that can alert, attract, or mask. Blue-spotted ribbon-tailed rays have striking electric blue spots on their skin, but the biological processes that give rise to these electric blue markings remain a mystery.
“If you see a blue colour in nature, you can be almost certain that it is not a pigment but rather a tissue nanostructure,” says Mason Dean, associate professor of comparative anatomy at City University of Hong Kong (CityU). “Understanding the structural colour of animals depends not just on optical physics, but also on the materials used, how precisely these are organised in the fabric, and how the colour appears in the animal’s environment. We brought together a wonderful interdisciplinary team from many countries to put all these pieces together, and as a result we have come up with a fantastic and fun solution to the stingray colour puzzle.”
Structural colors are not the product of chemical pigments, but are created by extremely small structures that direct light. “Blue colors are particularly interesting because blue pigments are extremely rare, and nature often uses nanoscale structures to create blue,” says Victoria Kamska, a postdoctoral researcher at CityU who studies natural color mechanisms. “We’re particularly interested in ribbon-tailed rays because, unlike most other structural colors, their blue color doesn’t change when you look at them from different angles.”
The research team combined different methods to understand skin architecture in different natural environments. “We used micro-computed tomography (micro-CT), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to understand the fine-scale architecture of the skin,” says Dean.
“We discovered that the blue color is produced by unique skin cells that have a stable three-dimensional arrangement of nano-sized spheres containing reflective nanocrystals (like pearls suspended in bubble tea),” says Amar Surapaneni, a postdoctoral researcher in Mason Dean’s group who was until recently a visiting lecturer at Trinity College Dublin. “Since the size and spacing of the nanostructures is a useful multiple of the wavelength of blue light, they tend to reflect blue wavelengths in particular.”
Interestingly, the team found that the unique “semi-ordered” arrangement of the spheres helps ensure color consistency across viewing angles. “And to wash out extraneous colors, the thick layer of melanin beneath the color-producing cells absorbs all other colors, resulting in extremely bright blue skin,” says Dr. Dean. “The result is a wonderful collaboration of the two types of cells: the structural color cells emphasize the blue color, and the melanin pigment cells suppress other wavelengths, resulting in extremely bright blue skin.”
The team believes this stunning blue colour may provide camouflage benefits for the stingrays. ‘Blue penetrates deeper into the water than other colours, helping the animals blend into their surroundings,’ says Dr Dean. ‘The bright blue spots on the stingrays’ skin don’t change depending on the viewing angle, so they may have particular camouflage advantages as the animal swims or manoeuvres quickly using undulating fins.’
Applications for this research currently under investigation include bio-inspired pigment-free color materials. “We continue to collaborate with our research colleagues to develop flexible biomimetic structural color systems inspired by the soft nature of stingray skin for safe, chemical-free colors in textiles, flexible displays, screens, and sensors,” Dean says.
In addition to working with rays, Dr. Kamska and his team are also investigating the blue coloration of other rays and sharks, including the blue shark. “Although the name ‘blue shark’ and its ecological aspects are well studied, no one yet knows how the blue coloration is generated in its skin,” Dr. Kamska says. “The initial results suggest that this coloration mechanism is different from that of the ray, but like the ray, we need to try different combinations of subtle imaging tools and take into account the various disciplines involved, such as optics, materials science and biology.”
This research is published in the journal Advanced Optical Materials “Ribbontail stingray skin uses Core-Shelf photonic glass ultrastructure to create blue structural color “.
Additionally, the journal Frontiers in Cell and Developmental Biology will publish a paper titled “” Intermediate filaments spatially organize intracellular nanostructures to generate the bright blue color of ribbon-tailed stingrays during ontogeny “.
Source: Port Altele
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