Tiny Water Bears, the World’s Toughest Animal, Have a Bizarre Genome

This tardigrade is nearly invisible to human eyes as its average body measurement is roughly 1.5 millimeters, which is also considered to be one of the toughest animals on the planet due to its ability to withstand extreme temperatures and weather conditions, from absolute zero degrees to more than 100 degrees Celsius. Researchers are discovering only the ones that have proven useful to the water bears, which suggests tardigrades may swap DNA more often than indicated by the new finding, Mark Welch says. Tardigrades may keep the best ones to enhance their survival. They have eight legs and they live in places populated with water, be they in Antarctica or near the sea.

The water bear that is scientifically known as the tardigrade, is the world’s toughest micro animal as scientists successfully sequenced the genome of the creature, revealing that almost one fifth of its DNA are foreign in origin.

“The tardigrades were found to have acquired about 6,000 foreign genes primarily from bacteria, plants, fungi and Archaea through a process called horizontal gene transfer”.

So what’s foreign DNA and why does it matter that tardigrades have so much of it? The closest comparison with the tardigrade is a microscopic form of plankton called a rotifer (pictured below, eating), which has about 9 per cent of its DNA from other organisms.

Co-author Bob Goldstein of UNC’s College of Arts and Sciences said that they had no knowledge that such an animal genome could be composed of so much foreign DNA.’ ‘We were familiar with many animals that obtain foreign genes, but had no clue that it happens to this level’. This, in turn, horizontal gene transfer creates a mosaic of genes in tardigrade.

Although, the scientists confirmed that the Tardigrade contains genetical material from different other organisms, including plants and bacteria, they could not say for sure which is which, because most of the genes have yet to been sequenced.

Researchers said the DNA likely gets inside the genome randomly but what remains allows water bears to survive in the most hostile environments. When tardigrades are desiccated, their DNA breaks into pieces. They can be repaired after they come back to normal situations.

As their cells rehydrate, their membranes and nuclei, where the DNA is located, can become “leaky” for a period of time, allowing DNA and some other molecules pass in and out easily, they explain.

This would be a random process, but the genes that get passed down would be those that help the animals survive.

“With horizontal gene transfer becoming more widely accepted and more well-known, at least in certain organisms, it is beginning to change the way we think about evolution and inheritance of genetic material and the stability of genomes”, said Boothby.

“Instead of thinking of the tree of life, we can think about the web of life and genetic material crossing from branch to branch”. “So it’s exciting. We’re just beginning to adjust our understanding of how evolution works”.