Bright eyes: Study finds reindeers' eyes change colour with Arctic seasons

The Biotechnology and Biological Sciences Research Council (BBSRC) funded team from UCL (University College London), and the University of Tromsø, Norway, showed that the colour change helps reindeer to see better in the continuous daylight of summer and continuous darkness of Arctic winters, by changing the sensitivity of the retina to light.

Arctic reindeer, like many animals, have a layer of tissue in the eye called the tapetum lucidum (TL) which lies behind the retina and reflects light back through it to enhance night vision.

By changing its colour the TL reflects different wavelengths of light.

In the bright light of summer the TL in Arctic reindeer is gold, similar to many other mammals, which reflects most light back directly through the retina.

However by winter it has changed to a deep blue which reflects less light out of the eye.

This change scatters more light through photoreceptors at the back of the eye, increasing the sensitivity of the retina in response to the limited winter light

The team believes this would be an advantage in the prolonged murk of winter, allowing reindeer to more easily detect moving predators and forage.

Lead researcher Professor Glen Jeffery from UCL, said: “This is the first time a colour change of this kind has been shown in mammals. By changing the colour of the TL in the eye reindeer have flexibility to cope better with the extreme differences between light levels in their habitat between seasons.

“This gives them an advantage when it comes to spotting predators, which could save their lives.”

The colour change may be caused by pressure within the eyes. In winter pressure in the reindeers' eyes is increased, probably caused by permanent pupil dilation, which prevents fluid in the eyeball from draining naturally. This compresses the TL, reducing the space between collagen in the tissue and thus reflecting the shorter wavelengths of the blue light common in Arctic winters.

Previous work from Professor Jeffery and Norwegian colleagues from Tromso had shown that Arctic reindeer eyes can also see ultraviolet, which is abundant in Arctic light but invisible to humans, and that they use this to find food and see predators.

The blue reflection from the winter eye is likely to favour ultra-violet sensitivity.

“Shifting mirrors: adaptive changes in retinal reflections to winter darkness in Arctic reindeer” is published in Proceedings of the Royal Society B, can be viewed online at http://dx.doi.org/10.1098/rspb.2013.2451 from October 30.

Notes to editors

Images available on request

Contact:

Chris Melvin, BBSRC Media Officer, 01793 414694, chris.melvin@bbsrc.ac.uk

About BBSRC

The Biotechnology and Biological Sciences Research Council (BBSRC) invests in world-class bioscience research and training on behalf of the UK public. Our aim is to further scientific knowledge, to promote economic growth, wealth and job creation and to improve quality of life in the UK and beyond.

Funded by Government, and with an annual budget of around £467M (2012-2013), we support research and training in universities and strategically funded institutes. BBSRC research and the people we fund are helping society to meet major challenges, including food security, green energy and healthier, longer lives. Our investments underpin important UK economic sectors, such as farming, food, industrial biotechnology and pharmaceuticals.

For more information about BBSRC, our science and our impact see: http://www.bbsrc.ac.uk

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About UCL (University College London)

Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender and the first to provide systematic teaching of law, architecture and medicine.

We are among the world's top universities, as reflected by our performance in a range of international rankings and tables. According to the Thomson Scientific Citation Index, UCL is the second most highly cited European university and the 15th most highly cited in the world.

UCL has nearly 27,000 students from 150 countries and more than 9,000 employees, of whom one third are from outside the UK. The university is based in Bloomsbury in the heart of London, but also has two international campuses – UCL Australia and UCL Qatar. Our annual income is more than £800 million.

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About University of Tromsø

UIT The Arctic University of Norway is the northernmost university in the world. Its location on the edge of the Arctic implies a mission. Climate change, the exploration of Arctic resources and environmental threats are topics of great public concern, and which the University of Tromsø takes special interest in. Our key research focuses on the polar environment, climate research, indigenous people, peace and conflict transformation, telemedicine, medical biology, space physics, fishery science, marine biosprospecting, linguistics and computational chemistry.