Water bears, the strange, eight-legged microscopic animals known to scientists as tardigrades, are thought to be nearly indestructible, able to survive some of Earth's most extreme environments.
Contrary to previous findings suggesting 17.5 percent of the critter's genome is made of foreign DNA, researchers from the University Edinburgh found tardigrades - also known as moss piglets - have not acquired a significant proportion of their DNA from other organisms.
To have foreign DNA means that the animals' genes would have come from creatures other than the animal itself. Instead, the latest analysis revealed that nearly all of what was mistaken for foreign DNA was simply bacterial contamination.
"What would in decades past have taken many months to sort out became the focus of experts around the world and has been swiftly resolved. We hope this paper will finally correct the scientific record," said Professor Mark Blaxter, of the University of Edinburgh's School of Biological Sciences, who led the study. "Tardigrades are amazing organisms, but these suggestions about their DNA were a step too far, even for their eight legs."
Water bears are tiny, microscopic animals that mostly live in mosses, lichens and liverworts, but some can also be found living in fresh water. They have eight legs with four claws on each, short and cylindrical bodies, and mouths with sharp, pointy teeth called stylets. When feeding, the animals use their teeth to cut into moss leaves or algae and then suck the plant's juices.
While these animals have long fascinated scientists for their ability to survive extremes of temperature, pressure, lack of oxygen, radiation exposure and even space, genome analyses suggesting tardigrades had the ability to pick up and reuse DNA from other species raised quite a bit of speculation.
Using new computational tools, researchers carefully analyzed the findings in explicit detail. Rather than a staggering 17.5 percent, their study confirms that less than one percent of tardigrades' genes are likely to have been borrowed from other species. This number, researchers say, is a bit more reasonable, as the genomes of most other animals have less than one percent foreign DNA - even humans have a few borrowed genes.
Their findings were recently published in the journal Proceedings of the National Academy of Sciences.
