Why can reindeer be "neighbors" with polar bears? Why is it currently the only domesticated deer

Source: North Evening New Vision Network

On the endless Arctic glacier, in addition to the well-known polar bear, there is also an animal called a reindeer, which is said to be pulling Santa's sleigh to thousands of households. However, the Arctic living environment is harsh, the winter temperature is cold and the food is poor, and what is more serious is that the Arctic region does not have a 24-hour day and night turnover, there is no "sunrise and sunset" rhythm of life, what can reindeer adapt to this and become a "neighbor" with the polar bear?

According to news from the Chinese Academy of Agricultural Sciences, the special animal nutrition and breeding innovation team of the Institute of Specialties of the Academy, together with the relevant teams of Northwestern Polytechnical University, Soochow University, Norwegian University of Life Sciences, Chinese Academy of Sciences and other units, recently revealed the molecular mechanism of reindeer adaptation to the Arctic environment. The research results have given people a more comprehensive and in-depth understanding of the adaptability of polar animals, provided important clues for the solution of some human health problems such as the effect of vitamin D on calcium deposition, the regulation of the biological clock to treat human sleep disorders, and also provided an important data basis for the subsequent development of reindeer protection.

On June 21, the results of this research were published in the international academic journal Science in the form of a long research paper, which is one of the three long articles published by Science at the same time as the research of the Ruminant Genome Research Program.

According to Li Zhipeng, corresponding author and associate researcher of the Institute of Special Products of the Chinese Academy of Agricultural Sciences, reindeer is the only species belonging to the suborder Ruminant, Deer Family, and Reindeer genus, mainly distributed in tundra, mountains and forest areas north of 48o north latitude in Eurasia, southern Siberia and North American continents, and is a typical representative of large ruminant fauna in the Arctic and subarctic regions. At present, China's reindeer are mainly distributed in the northwestern part of the Daxing'an Mountains, and are stocked by the Evenk people. Interestingly, unlike other deer, reindeer not only do males have horns, but females also grow horns.

However, prior to the release of this result, the molecular genetic mechanisms by which reindeer adapt to arctic extreme environments and female horns remained unclear. In addition, reindeer are currently the only domesticated deer, playing an important role in the development of some human civilizations, but where the "tame" genetic basis of reindeer comes from has not been known.

Based on the reindeer reference genome published by the same team earlier, the research team analyzed the genetic mechanism of reindeer's adaptation to arctic and docile characteristics through in-depth comparative genomics and evolutionary genome analysis based on data from two other papers of the Ruminant Genome Project.

Li Zhipeng said that through artificial selection signal analysis, the study found that the reindeer vitamin D metabolism pathway in the two key genes - POR and CYP27B1 - were strongly naturally selected, and the activity of the enzyme encoded by these two genes was much higher than that of goats and dwarf deer (roe deer), and the research team believes that this may greatly enhance the reindeer's ability to absorb calcium.

In addition, two other important genes called "lipoprotein transport" and "lipid synthesis" have also mutated in reindeer, and these two genes have also been reported in polar bear and penguin fat metabolism evolution studies, indicating that energy metabolism in different polar animals undergoes convergent evolution.

Li Zhipeng said that the reindeer's core regulatory gene in the rhythm pathway , PER2 , has a reindeer-specific mutation, resulting in the per2 gene being unable to bind to another rhythm core gene, CRY, causing the reindeer to lose the circadian molecular clock, so that they can adapt to the Arctic polar day and night environment.

The team also found that ccND1, a key gene for horn growth in reindeer, added a male hormone receptor binding region upstream, which the team believes may allow reindeer to grow horns at lower androgen levels.

Finally, the team found that genes in reindeer that are associated with the development, migration, and differentiation of neural crest cells are selected, rapidly evolved, or specifically mutated, and that neural crest cells are thought to be a key factor in domestication, "which is likely to be the reason for the reindeer's meekness." Li Zhipeng said.

reindeer

Reindeer (scientific name: Rangifer tarandus), also known as horned deer. It is the only animal in the genus Reindeer in the family Deer family. The body length is 100 to 125 cm, and the shoulder height is 100 to 120 cm. Both male and female have horns, and the complex branches of the horns are an important feature of their appearance. The long horns are intricately branched, sometimes more than 30 forks, the hooves are wide, the hanging hooves are well developed, and the tail is extremely short. The reindeer's body is covered with light but extremely cold-resistant fur. The coat color of different subspecies and sexes varies significantly in different seasons, from the dark tan of male North American woodland reindeer in the summer to the white of Greenland Island. The main coat colours are brown, off-white, floral white and white. Medium white is generally present on the abdomen, neck, and above the hooves

Reindeer are mainly found in the Arctic Rim region of the Northern Hemisphere, including in Eurasia and northern North America, as well as on some large islands. Reindeer in China are only found in the forest area northeast of the Daxing'anling Mountains. The Evenk people of China use reindeer as a means of transportation.