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The tardigrade genome has been sequenced, and it has the most foreign DNA of any animal

Scientists have sequenced the entire genome of the tardigrade, AKA the water bear, for the first time. And it turns out that this weird little creature has the most foreign genes of any animal studied so far – or to put it another way, roughly one-sixth of the tardigrade’s genome was stolen from other species. We have to admit, we’re kinda not surprised.

A little background here for those who aren’t familiar with the strangeness that is the tardigrade – the microscopic water creature grows to just over 1 mm on average, and is the only animal that can survive in the harsh environment of space. It can also withstand temperatures from just above absolute zero to well above the boiling point of water, can cope with ridiculous amounts of pressure and radiation, and can live for more than 10 years without food or water. Basically, it’s nearly impossible to kill, and now scientists have shown that its DNA is just as bizarre as it is.

So what’s foreign DNA and why does it matter that tardigrades have so much of it? The term refers to genes that have come from another organism via a process known as horizontal gene transfer, as opposed to being passed down through traditional reproduction.

Horizontal gene transfer occurs in humans and other animals occasionally, usually as a result of gene swapping with viruses, but to put it into perspective, most animals have less than 1 percent of their genome made up of foreign DNA. Before this, the rotifer – another microscopic water creature – was believed to have the most foreign genes of any animal, with 8 or 9 percent.

But the new research has shown that approximately 6,000 of the tardigrade’s genes come from foreign species, which equates to around 17.5 percent.

“We had no idea that an animal genome could be composed of so much foreign DNA,” said study co-author Bob Goldstein, from the University of North Carolina at Chapel Hill. “We knew many animals acquire foreign genes, but we had no idea that it happens to this degree.”

Dark ghost shark (Hydrolagus novaezealandiae) and the pale ghost shark (Hydrolagus bemisi), both are shortnose chimaera of the family Chimaeridae, found on the continental shelf around the South Island of New Zealand in depths from 30 to 850 m.

Both ghost shark species are taken almost exclusively as a bycatch of other target trawl fisheries