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article imageReindeer eyes change color in winter darkness

By Tim Sandle     Nov 1, 2013 in Environment
To survive the wintery conditions in the Arctic, scientists have found that one part of an reindeer’s eyes changes color. This adaptation increases the sensitivity of the animal’s vision, helping it navigate the through the darker months.
The change to the color of the eyes of reindeer is one facet of the animals' ability to adapt to changing conditions in the Arctic, especially the move towards the harsh winter. Other changes that take place include developing thick coats with two layers of fur; the pads on their hooves shrink in winter to give them better traction; and they have the ability to detect ultraviolet light, which helps them see in the months of near-total darkness.
The part of the eye that undergoes a color change is called the tapetum lucidum. This is the layer of tissue behind the retina that reflects light and helps an animal to better see in dim light. It’s sometimes referred to as the “cat’s eye” because it’s the layer that causes the eyes of a cat to glow at night when a small amount of light hits the eye.
In most mammals, this eyeshine is golden, and this includes reindeer in summer. However, in the winter a reindeer’s tapetum lucidum shines blue. The shift to blue increases the scatter of reflected light so it passes to more photoreceptors, thereby allowing the reindeer to make out more images under very dark conditions. At the same time as appearing blue, the reindeer pupils also dilate.
The new research into eye color changes was undertaken by teams based in Norway and England. The findings have been published in the Proceedings of the Royal Society B. The paper is titled "Shifting mirrors: adaptive changes in retinal reflections to winter darkness in Arctic reindeer."
More about Reindeer, Eyes, Color, Winter, Nose
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