So what if Rudolph, Donner and Blitzen and the rest of the crew can’t really fly? They and the herd have some truly amazing evolutionary adaptations that could inspire new treatments for human diseases
AS ANY young child knows, reindeer have a special superpower: they can fly. Or, at least, Rudolph and his eight sleigh-towing pals can. Reindeer first took to the skies in 1823, when Clement Clarke Moore published Twas the Night Before Christmas. He is said to have got his inspiration from the Sami people of northern Europe, whose shamans conjured up flying reindeer while in magic mushroom-induced trances.
Unfortunately, that’s all bunkum – even the bit about the Sami. But who needs fiction? Reindeer have real-world superpowers. The animals have evolved a whole range of amazing innovations that let them not just survive but thrive in the frigid Arctic. Their eyes change colour like living sunglasses, from gold in summer to blue in winter. They see the world in glorious ultraviolet. They can switch their body clocks on and off, produce lots of vitamin D even in limited sunlight and grow antlers up to a metre long in just a few months.
What’s more, we might be able to borrow some of those abilities. Discovering more about Rudolph could lead to new ways of tackling jet lag, insomnia and cancer, and even allow us to grow new limbs. Thanks to recent work revealing the genetic underpinnings of reindeer’s unusual traits, their superpowers could one day be ours.
Nearly 5 million reindeer roam the frozen north, from Alaska to Siberia and Greenland. The biggest group, containing about half a million animals, is the Taimyr herd of the Siberian tundra. Also known as caribou in North America, these lichen-eating ruminants are the only deer species to have been tamed by humans and about half are domesticated. On the Norwegian islands of Svalbard, males of the smallest subspecies weigh no more than 90 kilograms. In the forests of Finland, a stag can tip the scales at 250 kilograms.
Wherever they live, reindeer face challenges that would kill many other animals, including severe cold, limited food in winter and extremely prolonged periods of daylight and darkness. In June this year, some of the genes that allow them to overcome these problems were revealed in the first results from the Ruminant Genome Project. It compared reindeer DNA with that of other animals that chew the cud and identified mutations galore. “We were surprised to find so many unique gene variants related to reindeer’s adaptation to the Arctic environment,” says Zhipeng Li at the Chinese Academy of Agricultural Sciences.
“Many of the same genes are involved in the same processes in reindeer as they are in humans,” says Rasmus Heller at the University of Copenhagen, Denmark, who was also part of the project. Take the biological clock. Humans and most other animals have daily rhythms of activity and inactivity linked to light and dark, driven by the circadian clock. Reindeer do too, but they can override this. In the 24-hour daylight of an Arctic summer, they forage almost around the clock so they can put on as much weight as possible. In the dark depths of winter, their metabolic levels plummet and they have only short bouts of activity that don’t adhere to a 24-hour pattern.
They share this ability to break the rhythm of the circadian clock with other polar animals, including the emperor penguin and a type of grouse called the rock ptarmigan. “If you are an Arctic animal, you are faced with the weirdness of the light conditions,” says Heller. “This is a challenge for an animal that doesn’t have the genetic background to cope with it. It would mess with everything from hormone secretions to physiology.” The ruminant genome studies reveal what is going on in reindeer. They have unique versions of genes that drive circadian rhythms. In particular, this means one key protein called Per2 is mutated, so that another protein crucial for this regular cycle can’t bind to it. “A vital part of their biological clock malfunctions,” says Heller.
A cure for jet lag?
The discovery of these gene variants in reindeer could perhaps be exploited to help humans overcome jet lag, which results from having to readjust to the light/dark cycle in a different time zone. Disruptions to circadian rhythm are also thought to play a role in mood disorders such as depression.
The biological mechanisms underpinning how reindeer override their circadian rhythms could provide insight into sleeplessness, too. “There are specific gene variants involved in insomnia, and we can compare these with the genes from reindeer to further understand how people’s circadian rhythm is affected,” says Li.
Another impressive ability is the way both male and female reindeer grow new antlers every year. Aside from the placenta, deer antlers are the only mammalian organs that can be completely regenerated. A reindeer’s headgear can contain up to 10 kilograms of bone and blood vessels, and grows up to 2.5 centimetres a day. How do they achieve this?
Research published earlier this year provides an answer. “The genes that get turned on in cells destined to become antlers are also turned on in cancer cells” says Yunzhi Peter Yang, a tissue engineer at Stanford University in California. “Tissue regeneration and cancer growth are two sides of the same coin.” Yet reindeer are five times less likely to get cancer than other mammals because they have evolved highly efficient tumour suppression mechanisms that control the otherwise dangerous cancer pathways. This extraordinary ability makes them of great interest to researchers looking for new ways to prevent or treat cancer in humans.
Growing antlers also requires a lot of calcium, and that presents another challenge. To absorb calcium from food in the gut, mammals need vitamin D, which is made through the action of sunlight on skin. “It is particularly important for reindeer to maximise their calcium uptake and vitamin D production, but this is challenging in an environment where there is essentially no sunlight for half the year,” says Heller. The reindeer’s solution, the Ruminant Genome Project found, is a souped-up system for producing vitamin D that is far more efficient than ours.
Understanding how reindeer antlers grow might help us regenerate tissues in humans. “Can we borrow the same mechanisms for bone diseases such as osteoporosis or bone cancer?” says Yang. “There is so much potential.”
Some of it has already been realised: the way antlers are attached to the skull has inspired the design of a new kind of bone-anchored prosthesis for people missing limbs.
Flying and red noses are all very impressive but it turns out that the real reindeer powers are just as exciting – and, more importantly, they’re not just for Christmas.
First published at New Scientist. Wednesday 18 December 2019. See; https://www.newscientist.com/article/mg24432610-700-reindeers-real-superpowers-could-help-us-beat-depression-and-cancer/