Few as tough as Antarctic midge

Paris - Antarctica's only native insect, a minuscule midge, may rely on a no-frills genome to survive being frozen, dehydrated and blasted with radiation in an ultra-tough environment, scientists said on Tuesday.

Slightly bigger than a flea, the wingless bug spends most of its two-year larval stage frozen in the Antarctic ice before emerging for 10 days to mate and lay eggs on the continent's equally hostile surface, and then die.

Apart from resistance to freezing and intense ultraviolet radiation from the Sun, the midge can tolerate losing up to 70% of the water in its body cells. Most animals won't survive losing more than 20%.

"Few animals can boast of being as tough as the Antarctic midge," said a statement from Washington State University, which took part in a project to sequence the midge's genome.

What the team found surprised them - the midge's genome was the smallest yet observed in an insect.

"It's tiny," said Joanna Kelley of the university's school of biological sciences and one of the study authors. "That was a huge surprise."

Scientists had previously observed a link between animals living in freezing conditions and large genomes thought to reflect the evolutionary adaptations they had undergone.

But this midge's genome had only 99 million base pairs, compared for example to 105 million for the body louse or 3.2 billion for humans.

"We suspect that it's somehow an adaptation to the extreme environment," said Kelley, though this has not been confirmed.

The midge, known in the scientific community as Belgica antarctica, lacks much of the so-called "junk DNA" - repetitive sequences and shorter stretches of non-encoding DNA - that all insects and animals have.

Only terrestrial animal

But it has a similar number of functional genes to most flies, about 13 500.

"It has really taken the genome down to the bare bones and stripped it to a smaller size than was previously thought possible," said study co-author David Denlinger of The Ohio State University.

It did, however, have an abundance of genes associated with developmental processes, metabolism and response to external stimuli, "which may reflect adaptations for surviving in this harsh environment."

The midge is the only fully terrestrial animal endemic to Antarctica - the southernmost continent isolated about 33 million years ago with a cold, inhospitable desert environment.

Belgica antarctica eats bacteria, algae and nitrogen-rich waste produced by penguins, and has no predators.

Denlinger said the findings may have implications for humans in the long term "by revealing how human tissue harvested for transplant could be sustained in cold storage."

The findings were published in the journal Nature Communications.