英语听力文摘 English Digest 731 麋鹿眼睛为何可以变色？（在线收听）

Reindeer Eyes

Rudolph the reindeer is best known for his brightly colored red nose. For other reindeer, however, the most colorful thing about them is actually their eyes. Researchers have found that depending on the season, the eyes of Arctic reindeer change from gold to blue.

Tapetum Lucidum

Like many mammals, Arctic reindeer have a structure in the eye called the tapetum lucidum, TL for short. It sits behind the retina and reflects light back to increase the sensitivity of night vision. The TL is also responsible for reindeer eye color changes.

During the Arctic summer, when it’s always light outside, reindeer TL is gold — a color that reflects more light back through the retina, better enabling reindeer to see in daylight. (This is why, by the way, many mammals have gold colored eyes.)

When Darkness Reigns

But when the Arctic winter sets in and darkness reigns, the TL turns blue. The result of this is less light reflecting back out through the retina, making it easier for the animals to see predators in dim conditions.

The color change may be caused by shifting pressure in reindeer eyes, which stems from constant pupil dilation. When compressed, the TL reflects shorter wavelengths of blue light which are more plentiful during Arctic winters.

驯鹿鲁道夫以其鲜艳的红色鼻子而闻名。然而，对于其他驯鹿来说，它们最多彩的地方其实是它们的眼睛。研究人员发现，根据季节的不同，北极驯鹿的眼睛会从金色变为蓝色。

透明绒毡

和许多哺乳动物一样，北极驯鹿的眼睛有一种叫做绒毡层灵芝的结构，简称TL。它位于视网膜后面，反射光线以增加夜视的灵敏度。TL还负责驯鹿眼睛颜色的变化。

在北极夏季，当外面总是很亮的时候，驯鹿的TL是金色的，这种颜色可以通过视网膜反射更多的光线，从而更好地让驯鹿在白天看到东西。（顺便说一句，这就是为什么许多哺乳动物都有金色的眼睛。）

当黑暗降临

但当北极的冬天来临，黑暗笼罩时，TL就会变成蓝色。这样做的结果是，通过视网膜反射回来的光线减少，使得动物在昏暗的环境中更容易看到捕食者。

这种颜色的变化可能是由于驯鹿眼睛的压力变化引起的，这是由于瞳孔不断扩大造成的。压缩后，TL反射的蓝光波长更短，在北极冬季更为充足。