As we all know, a dog can hear tones beyond our auditory range and has a keener sense of smell. Other species outdo us as well as each other in other aspects of the senses. Elephants perceive tones pitched lower than those heard by humans or dogs, and rats have more scent receptors. The sensuous attunement of mammalian ears and noses varies widely. Yet vision is relatively constant among species. Though some birds and insects have extreme ranges of vision, mammalian vision is limited to what’s called the visual spectrum, light ranging from 400 to 700 nanometers in wavelength, from violet to red in color.
An exception to that general rule has long been suspected and has just been assessed by scientists at the University College London and the University of Tromsø, Norway. The researchers found that Arctic reindeer see light a fifth shorter in wavelength than that seen by humans, as well as most mammals. Reindeer see what we see, as well as a greater part of the ultraviolet spectrum, sometimes called “black light,” because we can’t see it. (The purple glow of artificial black-light sources, such as fluorescent lamps, is not ultraviolet light, but rather violet light in the visible spectrum that isn’t filtered out by the glass envelope of the lamp.)
The ability to see in ultraviolet helps reindeer survive in the Arctic, principally because lichens, the staple of their winter diet, do not reflect ultraviolet light. So, to a forging reindeer, food stands out black in a snowscape. Moreover, urine, a sign of predators or potential mates, and the fur of predators appear in sharp contrast in ultraviolet.
Seeing ultraviolet has a significant side effect. Reindeer are immune to photokeratitis, a painful eye condition caused by exposure to ultraviolet light. In humans, photokeratitis is commonly known as snow blindness, because people often suffer it after having been on snow, which strongly reflects ultraviolet light. So, ever since people took to living in snow-covered landscapes, they have devised various remedial means of cutting down the amount of ultraviolet light reaching the eye. Historically first were the snow goggles devised by Arctic peoples, including the Inuits (North America and Greenland), the Sámi (northern Scandinavia and Russia) and the Nenets (Siberia). Like a permanent squint, the native snow goggles cut down all light reaching the eye by covering each eye with a cup fashioned from reindeer antler, wood or shell, with a thin slit to allow some vision. The cups were held in place by straps made of reindeer sinew. Modern snow goggles use various types of glass and plastic with built-in filters that block ultraviolet but otherwise allow full vision.
Humans took a few centuries to evolve ways of protecting their eyes against the harmful effects of ultraviolet light. Reindeer gained their ability to cope with ultraviolet after they migrated to the Arctic ten thousand years ago. They are not alone, as snow blindness is unknown in Arctic animals. Moreover, no Arctic animal exhibits photophobia, the fear of light exposure often found in ultraviolet-sensitive rodents. The reasons for these differences from similar animals elsewhere on the planet are unknown, but it’s clear that Arctic vision adaptation may be evidence of evolution in the fast lane.
The complete details of the reindeer vision research are reported in an article by C. Hogg et.al. in issue 214 (June 15, 2011) of the Journal of Experimental Biology, Digital Object Identifier (DOI): 10.1242/jeb.053553 (access DOI via www.doi.org).
M. Michael Brady lives in a suburb of Oslo, where he works as a translator. A natural scientist by training, he takes his vacations in France. Dateline: Europe appears monthly in MG.