World News | How reindeer’s eyes transform in winter to give them twilight eyes

LONDON, July 2 (Conversation) Reindeer are loved around the world for their deep and expressive eyes, majestic antlers and magical connection to Santa Claus. The moment you learn the grim truth of how Christmas gifts get under the tree is a harrowing thing that will torment many childhoods. But reindeer is more special than your cynical older siblings or classmates would have you believe.

The Arctic caribou, like its main predator, the wolf, is well adapted to its snowy homeland, where winter conditions can see temperatures dropping to -50°C and low levels of daylight. Reindeer have a second coat of fur and broad, crescent-shaped hooves for stability and digging in the snow. As our new research shows, their eyes physically change with the seasons, which allows them to see clearly in the long winter twilight.

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Midwinter in the Arctic is either dark or twilight, when the sun is below the horizon all day. Reindeer need to seek and discover their winter food, lichens, by brushing their hooves, antlers and mouths across the snow-covered ground. Lichens thrive in the Arctic – an ideal food source for reindeer wherever they go.

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Twilight is special

Reindeer forage in the twilight as wolves hunt. However, twilight has a unique property that distinguishes it from day or night: it is very blue, containing very little green, yellow and orange.

That’s because, illuminated by the sun below the horizon, Earth’s ozone layer acts as a filter across the sky, absorbing nearly all but blue light in twilight. Sunlight travels farther through the atmosphere, horizontally across the ozone layer. This ozone blue is different from the clear sky blue during the day, which is caused by the scattering of sunlight by air molecules.

Although artists refer to the period after sunset as the “blue hour,” we tend not to notice it as our eyes adjust to slowly changing colors. As darkness approaches, our vision shifts from relying on the cones that provide us with color vision to using the more sensitive rods for color blindness. In winter, dusk in polar habitats can last more than a third of the time.

Both wolves and reindeer have increased their sensitivity to arctic twilight through “mirrors” behind their retinas. When light enters the eye and travels through the retina, not all light is detected and absorbed by special neurons called photoreceptors. Instead, the mirror reflects it back through the retina a second time, when more light is detected. The image the reindeer sees is brighter but slightly blurry because the mirror scatters some light sideways, kind of like fogged glass.

This is an advantage in dim light, as animals rely more on visual contrast and movement than visual clarity. This mirror is called tapetum (shiny carpet) and has evolved independently in many animals. Important exceptions include humans and raptors that require sharp images.

eyes that change with the seasons

Our study compared the eyes of reindeer that died in summer with those of reindeer that died in winter.

Research has shown that the tapetum of reindeer’s eyes undergoes unique seasonal changes and changes color, reflecting golden turquoise light in summer and deep blue in winter. Both lichen and wolf fur reflect less blue than other colors, so they appear dark in snow-covered landscapes.

The tapetum of the reindeer adopts the same structure as the iridescent feathers of the peacock, the bright blue wings of the morpho butterfly and the sparkling colors of the opal gemstones. This is called structural coloring.

In the reindeer tapetum, these structures are very fine collagen fibers that cannot be seen under a light microscope, similar to but finer than muscle structures. Think of these fibers as masses of pencils, neatly stacked in a hexagonal transparent box.

Get enough water to fill the gap, reducing the scale by a factor of about 40,000, and the box will reflect blue light. This represents the winter tape felt layer. To convert to summer tapetum, increase the water volume tenfold and double the depth of the box. At this tiny scale, the fibers will roughly retain their hexagonal pattern, but there will be more gaps between them.

We believe this transition is triggered by changes in reindeer eye pressure that occur during summer and winter.

Another way to think of it is as a reindeer eye with summer and winter tires. In very cold conditions, you can let the tires vent some air to increase traction on the ice. Reindeer let fluid flow out of the tapetum to get a better view of their surroundings.

The discovery could help engineers make products that change the color of reflections. The opportunities are endless. If you use a surface coated with reflective nanostructures (similar to reindeer tapestry), rather than a pigment-based paint, you can change the color by varying the spacing of the scaled “pencils” that reflect light. For example, you can change the color of a car by adjusting the separation. Unlike many pigments, these structural paints do not fade over time.

So while reindeer have long inspired Christmas traditions around the world, now they can inspire technology and science. (conversation)

(This is an unedited and auto-generated story from the Syndicated News feed, the body of the content may not have been modified or edited by LatestLY staff)