Winter Vision / Anne-Marie Hodge

Ely The northern ones are able to identify predators and find food against the background of the snow thanks to an extraordinary ability: vision in ultraviolet

Ultraviolet radiation (UV) is dangerous for humans: we cannot see it, but it is present in everything and increases our chances of getting skin cancer, cataracts and other diseases. It is mainly harmful in the northern part of the planet, where the depleting ozone layer blocks the ultraviolet rays less and the snow and ice return them to us. Biologists have therefore wondered how arctic mammals have adapted to the increased UV exposure, an adaptation that allows them not only to withstand the extreme lighting conditions of the poles, but also to derive an evolutionary advantage from them.

A study conducted in northern elk shed some light on the answer to the question. Glen Jeffrey and his colleagues from University College London and the University of Tromsø in Norway presented evidence that this animal, one of the symbols of the Arctic Circle, is not only immune to eye damage due to exposure to strong UV radiation, but is also able to sense ultraviolet light. Only a few mammals, from different families, are endowed with such vision, including several species of rodents, bats and marsupials. The researchers published their findings in the Journal of Experimental Biology.

Credit: National Oceanic and Atmospheric Administration

The ability to see UV gives the reindeer some notable advantages. The moose's main food source in winter, lichens, and the white fur of their main enemies, the wolves, absorb ultraviolet light. Thanks to their unique vision, the most important resources and dangers for reindeer are revealed before their eyes from the snowy landscape.

Ultraviolet vision has deep roots in the mammalian genealogy: early mammals that lived tens of millions of years ago had a short-wavelength-sensitive visual receptor, SWS1. Sensitivity was probably shifted to longer wavelengths in visible light, away from short-wavelength UV radiation, because most mammals back then were nocturnal and ultraviolet vision is useless at night. The fact that UV vision was shared by all ancient mammals could explain how a small but diverse group of animals reacquired the trait. If the scientists succeed in finding out how the reindeer's eyes are protected from the harmful effects of ultraviolet radiation, it is possible that new ways will be found to treat vision loss in humans. The average person loses 20% to 30% of their central photoreceptors during their lifetime. Most of the damage is due to exposure to light.

"We may learn how to better treat the loss of retinal cells that accompanies puberty, and perhaps also age-related macular degeneration," says Jeffrey. Meanwhile, the discovery that the reindeer see ultraviolet light and are also immune to the damage of this strong radiation sheds new light on the question of the Arctic animals' adaptation to one of the most extreme habitats in the world.

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