Reindeer See Wonderful World of UV Light

The ultraviolet light that can cause temporary snow blindness in humans can be life-saving for reindeer in the Arctic.

A team of researchers has now tested the vision of reindeer to see what wavelengths they can see and has found that they can perceive wavelengths down to around 350 to 320 nm, in the ultraviolet range.

The Biotechnology and Biological Sciences Research Council (BBSRC)funded team conducted the study, which shows that this visual capacity is part of the reindeer's unique adaptation to the extreme Arctic environment it inhabits. The UV range allows the animals to take in live-saving information in conditions where normal mammalian vision would leave them vulnerable to starvation, predators and territorial conflict. It also raises the question of how reindeer protect their eyes from UV radiation, which is thought to be harmful to human vision.

Lead researcher professor Glen Jeffery said, "We discovered that reindeer can not only see ultraviolet light but they can also make sense of the image to find food and stay safe. Humans and almost all other mammals could never do this, as our lenses just don't let UV through into the eye.

"In conditions where there is a lot of UV — when surrounded by snow, for example — it can be damaging to our eyes. In the process of blocking UV light from reaching the retina, our cornea and lens absorb its damaging energy and can be temporarily burned. The front of the eye becomes cloudy, and so we call this snow blindness. Although this is normally reversible and plays a vital role to protect our sensitive retinas from potential damage, it is very painful."

Winter in the Arctic are very severe; the ground is covered in snow, and the sun is very low on the horizon. At times, the sun barely rises in the middle of the day. Under these conditions, light is scattered such that the majority of light that reaches objects is blue or UV. In addition, snow can reflect up to 90 percent of the UV rays that falls on it.

"When we used cameras that could pick up UV, we noticed that there are some very important things that absorb UV light and therefore appear black, contrasting strongly with the snow. This includes urine — a sign of predators or competitors; lichens — a major food source in winter; and fur, making predators such as wolves very easy to see despite being camouflaged to other animals that can't see UV," said Jeffery.

This research raises questions about the effect of UV on eye health. It had always been assumed that human eyes block out potentially harmful UV. In human eyes, UV could damage sensitive photoreceptors, which are irreplaceable. However, UV light helps reindeer use information effectively and doesn't harm their eyes.

"The question remains as to why the reindeer's eyes don't seem to be damaged by UV. Perhaps it's not as bad for eyes as we first thought? Or maybe they have a unique way of protecting themselves, which we could learn from and perhaps develop new strategies to prevent or treat the damage the UV can cause to humans," Jeffery said.

"We can learn a lot from studying the fundamental biology of animals and other organisms that live in extreme environments. Understanding their cell and molecular biology, neuroscience and other aspects of how they work can uncover the biological mechanism that meant they can cope with severe conditions," said Douglas Kell, chief executive of BBSRC. "This knowledge can have an impact on animal welfare and has the potential to be taken forward to new developments that underpin human health and well-being."

For more information, visit: www.bbsrc.ac.uk