May 27, 2011

Reindeer Use Ultraviolet Light Vision For Survival

Harmful to humans, but life-saving for artic reindeer, ultraviolet light is a unique adaptation to the extreme artic environment in which reindeer live, according to a study published in the Journal of Experimental Biology.

"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," says lead researcher Professor Glen Jeffery of University College London. "Humans and almost all other mammals could never do this as our lenses just don't let UV through into the eye."

He continues, "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."

Researchers tested the reindeer's vision to see what wavelengths were visible to them and found that they are capable of handling wavelengths as low as 350 to 320nm, which is considered ultraviolet or UV.

Humans are only capable of seeing light with wavelengths ranging from around 700nm, which is equivalent to the color red, down to all of the colors of the rainbow which stops at 400nm, which corresponds to the color violet.

To test the UV light vision of reindeer, researchers had to first establish that UV light was able to pass through the lens and cornea of the animal's eye by firing through a dissected sample, reports BBC News.

The result revealed that light with wavelengths of about 350 did indeed pass through the reindeer eye.

Researchers then focused their study on proving that reindeer could actually "see" the light by testing the electrical response of the retina of anaesthetized reindeer to UV light.

"We used what is called an ERG (electroretinography), whereby we record the electrical response to light by the retina by putting a little piece of gold foil on the inside of the eyelid," Jeffery tells BBC News.

The test indeed revealed that the photoreceptor cells or "cones" in the reindeer's retina did respond to UV light.

UV vision is believed to aid the reindeer in distinguishing food and predators in the "white-out" of the Artic winter snow and the twilight of spring and autumn, according to the researchers.

"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," says Jeffery.

The study raises interesting questions regarding the effect of UV on eye health. Just as UV cause damage to our skin, it is assumed that the human eye is potentially harmed by these lights. UV could damage human sensitive photoreceptors that cannot be replaced, leading to irreversible damage to human vision, says the study.

However, how is it that artic reindeer are able to let UV into their eyes and use it effectively in their environment without suffering any consequences?

"Perhaps it's not as bad for eyes as we first thought?" suggests Jeffery. "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."

Professor Douglas Kell, chief executive of BBSRC, the organization that funded the study, says, "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. 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 wellbeing."


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