Inside the Bizarre Genome of the World’s Toughest Animal
Tardigrades are
sponges for foreign genes. Does that explain why they are famously
indestructible?
The toughest animals in the world aren't bulky
elephants, or cold-tolerant penguins, or even the famously durable cockroach.
Instead, the champions of durability are endearing microscopic creatures
called tardigrades, or water bears.
They live everywhere, from the tallest mountains to
the deepest oceans, and from hot springs to Antarctic ice. They can even
tolerate New York. They cope with these inhospitable environments by
transforming into a nigh-indestructible state. Their adorable shuffling gaits
cease. Their eight legs curl inwards. Their rotund bodies shrivel up, expelling
almost all of their water and becoming a dried barrel called a “tun.” Their metabolism
dwindles to near-nothingness—they are practically dead. And in skirting the
edge of death, they become incredibly hard to kill.
In the tun state, tardigrades don't need food or
water. They can shrug off temperatures close to absolute zero and as high as
151 degrees Celsius. They can withstand the intense pressures of the deep
ocean, doses of radiation that would kill other animals, and baths of toxic
solvents. And they are, to date, the only animals that have been exposed to the
naked vacuum of space and lived to tell the tale—or, at least, lay viable eggs.
(Their only weakness, as a researcher once told me, is “vulnerability to
mechanical damage;” in other words, you can squish ‘em.)
Scientists have known for centuries about the
tardigrades’ ability to dry themselves out. But a new study suggests that this ability might have
contributed to their superlative endurance in a strange and roundabout way. It
makes them uniquely suited to absorbing foreign genes from bacteria and other
organisms—genes that now pepper their genomes to a degree unheard of for
animals.
Thomas Boothby from the University of North
Carolina at Chapel Hill made this discovery after sequencing the first ever tardigrade genome, to better
understand how they have evolved. Of the 700 species, his team focused on Hypsibius
dujardini, one of the few tardigrades that’s easy to grow and breed in
a lab.
At first, Boothby thought his team had done a poor
job of assembling the tardigrade’s genome. The resulting data was full of genes
that seemed to belong to bacteria and other organisms, not animals. “All of us
thought that these were contaminants,” he says. Perhaps microbes had snuck into
the samples and their DNA was intermingled with the tardigrade’s own.
But the team soon realized that these sequences are
bona fide parts of the tardigrade’s genome.
