These are amazing animals.

http://www.eurekalert.org/pub_releases/2015-11/uonc-ahc111815.php

Public Release: 23-Nov-2015
A huge chunk of a tardigrade's genome comes from foreign DNA
Tardigrades, nearly microscopic animals that can survive the harshest of environments, including outer space, hold the record for the animal that has the most foreign DNA
University of North Carolina at Chapel Hill

Researchers from the University of North Carolina at Chapel Hill have sequenced the genome of the nearly indestructible tardigrade, the only animal known to survive the extreme environment of outer space, and found something they never expected: that they get a huge chunk of their genome - nearly one-sixth or 17.5 percent - from foreign DNA.

"We had no idea that an animal genome could be composed of so much foreign DNA," said co-author Bob Goldstein, faculty in the biology department in UNC's College of Arts and Sciences. "We knew many animals acquire foreign genes, but we had no idea that it happens to this degree."

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First author Thomas Boothby, Goldstein and their collaborators revealed that tardigrades acquire about 6,000 foreign genes primarily from bacteria, but also from plants, fungi and Archaea, through a process called horizontal gene transfer - the swapping of genetic material between species as opposed to inheriting DNA exclusively from mom and dad. Previously another microscopic animal called the rotifer was the record-holder for having the most foreign DNA, but it has about half as much as the tardigrade. For comparison, most animals have less than one percent of their genome from foreign DNA.

"Animals that can survive extreme stresses may be particularly prone to acquiring foreign genes -- and bacterial genes might be better able to withstand stresses than animal ones," said Boothby, a postdoctoral fellow in Goldstein's lab. After all, bacteria have survived the Earth's most extreme environments for billions of years.

The team speculates that the DNA is getting into the genome randomly but what is being kept is what allows tardigrades to survive the harshest of environments, e.g. stick a tardigrade in a - 80 celsius freezer for a year or 10 and it starts running around in 20 minutes after thawing.

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