Unique characteristics of reindeer include a diet consisting mainly of lichens and the ability to distinguish ultraviolet light, which is quite surprising for high latitudes. A new study directly linked one to the other. Its authors believe that deer change the reflective color of their fundus (tapetum) from yellow to blue in winter to see the ultraviolet part of the spectrum and find lichens in the snow.

reindeer (Rangifer tarandus) has become one of the symbols of northern ecosystems (both Eurasia and North America). This is a large even-toed animal that lives in large herds and inhabits the tundra and taiga zones. The importance of reindeer for the nature of the North cannot be underestimated, and in some places it is no less important for small nations still engaged in reindeer herding.

Reindeer are notable for many unique adaptations that allow them to perfectly adapt to harsh conditions and cover a large area. They feed on lichens, for example – “deer moss” or yagel. This strange and not very nutritious food is not suitable for everyone, but where there is little of it, it serves as a reliable source of energy and nutrients.

Another rather mysterious adaptation of the reindeer is the claimed ability to distinguish ultraviolet light. It is associated with special cornea and lens in most diurnal animals that actively absorb light in the ultraviolet range and protect the sensitive retina from harmful radiation. At the same time, a reindeer’s eye transmits up to 60 percent of light in the ultraviolet part of the spectrum.

In addition, reindeer have a special tape (tapetum lucidum in Latin). This is a layer of the eye’s choroid that hides behind the retina beneath its surface. The tapetum contains guanine crystals and various pigments and works as a light reflector; It is this eye membrane that allows the eyes of cats, dogs and other vertebrates to shine brightly in the dark. In this way, some of the light entering the eye is reflected and the animal sees better in semi-darkness.

The reindeer’s bantu is unique: It changes color with the season. In summer, their bands have the usual yellowish or golden color for animals, but turn blue in winter. As a result, it reflects not only visible light, but also ultraviolet light, which can well stimulate the photosensitive cones of the retina.

Ultraviolet radiation is seen by many insects and vertebrates that are active at night, such as bats. So why did reindeer need such an adaptation? The authors of a new article in the journal addressed this question i-Perception.

The authors state that active absorption of ultraviolet should be expected to be faster in the cornea and lens of animals in polar regions. Indeed, a person or animal living among permanent snow receives a double dose of ultraviolet light directly from the sun and reflected from the snow. It can damage your eyes, which is why winter sports enthusiasts wear sunglasses. For the same reason, reindeer in captivity often suffer from cataracts.

Scientists believe that reindeer have learned to distinguish between ultraviolet (and only in winter) in order to find their main food in the cold season – “reindeer moss”, aka Yagel. This is the name given to a number of lichens, that is, organisms consisting mainly of an inseparable symbiosis of a fungus and an algae of the genus Cladonia (cladonia) and cetraria (cetraria). Deer specifically eat deer cladonia (Cladonia rangiferina), which is reflected in both the Russian and Latin name lichen.

Cladonia resembles tough whitish shrubs or trees up to 12 centimeters high. It has a unique chemical composition and taste but also contains many proteins, fats and other nutrients. It is not difficult to notice them in the summer, but in winter and spring it is much more difficult to find off-white lichens against the same background. Most likely, it was jageldi that caused the emergence of “seasonal ultraviolet vision” in reindeer.

Lichens vary greatly in the rate at which they absorb different wavelengths of light, so some may be invisible in UV light. Therefore, the authors confirmed their assumption by describing the absorption spectrum of wild plants. C. rangiferina Lichen is from the Northern Highlands of Scotland, famous for its biodiversity. Cladonia turned out to be easiest to see in conditions of twilight light in the range of 330-370 nanometers, which corresponds almost to ultraviolet. It is he who is adapted to avert and most likely distinguish the unique eyes of the reindeer.