They say tests on reindeer showed that the animal does respond to UV stimuli, unlike humans. The ability might enable them to pick out food and predators in the "UV-rich" Arctic atmosphere, and to retain visibility in low light. Details are published in the The Journal of Experimental Biology.
UV light is invisible to humans. It has a wavelength which is
shorter (and more energised) than "visible" light, ranging from 400
nanometres down to 10nm in wavelength.
The researchers first established that UV light was able to
pass through the lens and cornea of the reindeer eye by firing light
through a dissected sample. The tests showed that light down to a
wavelength of about 350nm passed into the eye.
They then sought to prove that the animals
could "see" the light, by testing the electrical response of the retina
of anaesthetised 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," co-author
Professor Glen Jeffery of University College London told BBC News.
The tests showed that photoreceptor cells or "cones" in the retina did respond to UV light.
"If you're a bumblebee, you wouldn't think much of what this
animal is doing because it's seeing in what's called 'near UV' (about
320 to 400nm), but that's still very high energy stuff.
"The researchers believe UV vision could enable the reindeer to
distinguish food and predators in the "white-out" of the Arctic winter
and the twilight of spring and autumn.
Lichen, on which the animal feeds, would appear black to
reindeer eyes, they say, because it absorbs UV light. The animal's
traditional predator, wolves, would also appear darker against the snow,
as their fur absorbs UV light.
Urine in the snow would also be more discernable in UV
vision, which might alert reindeer to the scent of predators or other
Neither did the animal appear to suffer any damage as a
result of seeing in UV, say the researchers, or suffer the "snow
blindness" humans can experience in the UV-rich Arctic environment.
Professor Lars Chittka of Queen Mary University London, who
has explored the UV capabilities of bees, said the study showed what we
call the "visible" spectrum did not apply to most of the animal kingdom.
"It's further evidence that UV sensitivity across animals is
the rule rather than the exception, and that humans and some other
mammals are actually a minority in not having UV sensitivity," he said.
Professor Chittka was not surprised the UV light appeared to
do no damage to the reindeer retina. He said the tests suggested the eye
would only admit lower-frequency UV light ("UV-A light") rather than
more damaging higher-frequency light ("UV-B").
Further modelling and behavioural tests would also be needed
to verify that reindeer's apparent capacity to detect UV light really
did result in "better detection of predators and arctic lichens", he
The same research team which conducted the reindeer tests
will soon repeat the same experiments on seals to see whether they can
see into the UV region. Professor Jeffery believes many Arctic animals
are likely to have the capacity.
"There's no evidence that Arctic foxes or polar bears suffer
from snow blindness, so I bet you that most of the Arctic animals up
there are seeing into UV."
Please click here to view the original story.
Tests show Arctic reindeer 'see in UV' (BBC News)
Fri, May 27, 2011
Arctic reindeer can see beyond the "visible" light spectrum into the ultra-violet region, according to new research by an international team.