Why do Reindeer eyes change color?

Reindeer (Caribou) are the only mammals known to undergo a complete physical restructuring of the tapetum lucidum - the reflective layer behind the retina that causes "eyeshine." In the summer, a reindeer's eyes reflect a golden-yellow light. But in the dark, 24-hour night of the Arctic winter, their eyes turn a deep, rich blue. This isn't just a trick of the light; the internal pressure of the eye changes due to the constantly dilated pupil. This pressure squeezes the collagen fibers in the tapetum closer together, shifting the wavelength of light they reflect. The evolutionary reason for this is brutally practical: Ultraviolet vision. The blue eye allows UV light to hit the retina. Why do they need to see UV? Because lichen (their main food) and wolf urine absorb UV light, appearing stark black against the blinding white UV-reflective snow. In the winter darkness, a reindeer is essentially looking at a landscape where every spot a predator has marked territorv is a alowina black beacon

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Видео Why do Reindeer eyes change color? канала TheAngryNature