Tardigrades, also known as water bears, are nearly indestructible because one-sixth of their genetic material comes from other species, of which 90 percent comes from bacteria, scientists found after sequencing the animals’ DNA.
Water bears are microscopic animals that can survive extremely cold temperatures, boiling water, and may even survive in space. They can in fact be frozen for up to 10 years and not die.
After sequencing the genome of the water bears, the scientists found that approximately 17.5 percent of their DNA actually came from other species.
Biologist Bob Goldstein, of the University of University Of North Carolina in Chapel Hill and co-author of the study, said that he and his fellow researchers had no idea that an animal genome could have so much foreign DNA. They knew that a lot of animals acquired foreign genes, but they never thought that it was to that degree, he added.
In the research – published Monday in the journal Proceedings of the National Academy of Sciences – the scientists found that water bears have about 6,000 foreign genes, most of which come from bacteria. Some of the genes come from fungi, plants, and Archaea (single-celled microorganisms).
The genome of on organism can acquire foreign DNA through a process known as horizontal gene transfer (HGT). During that process, the species transfer their genes directly to one another, and not like in traditional reproduction where the genes are transferred from the parental generation to offspring through sexual or asexual reproduction.
Researchers at the University Of North Carolina in Chapel Hill suggest that the water bears’ defence mechanism helps with the transfer of foreign DNA. The animals tend to curl up when they find themselves in stressful situations, they expel their water, and their metabolism shuts down almost completely.
Their DNA than splits into small pieces, the researchers say. When the water bears regain consciousness they rehydrate, absorbing molecules around them and with that foreign genes.
Thomas Boothby, a professor at the University Of North Carolina in Chapel Hill said that this occurrence of horizontal gene transfer may change the way in which people look at evolution. Instead of viewing it as the tree of life, we should think of it as the web of life, Boothby said.
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