Santa Claus is often associated with his flying reindeer pulling his sled through the Christmas night. The story apparently comes from the 1837 poem “A Visit from St. Nicholas” by Clement Clarke Moore. The poem describes the original magical reindeer, but Rudolf would only be added in 1939 by Robert L. May in the “Rudolph the Red-Nosed Reindeer” little story.
Apart from featuring in poems and stories, reindeer (Rangifer tarandus), or caribous in North America, is a species of deer (duh…) distributed around the polar circle native to arctic, subarctic, tundra, boreal, and mountainous regions of northern Europe, Siberia, and North America. There are 14 subspecies of reindeer which vary in size, color and heard size. The largest heard is found in Russia composed of the migrating tundra reindeer Taimyr herd, R.t. sibiricus, and has a size varying between half and a million individual.
In the heart of winter the diet of reindeer is mainly based on lichens (here). Lichenans, the main polysaccharids of lichen, are degraded to glucose by a lichenase (here is the 1918 paper!) which is found in the reindeer stomach. It is unclear where this enzyme is coming from, though (in my short lit review) my best guess would be that it comes, of course, from a unique gut microbiome composition which helps the reindeer digest the lichen compounds they graze on. A few studies have already explored the microbial community compositions (here and here), and the polysaccharid utilisation loci (here).