The award for the tiniest insect genome in nature goes to an insect living in extreme conditions in Antarctica, a tiny wingless midge with a lifespan of less than a week, scientists say.
The Antarctic midge has only 99 million of the DNA building blocks known as nucleotide base pairs, less than any other creature and just a fraction of the human genome's 3.2 billion base pairs, they say.
The midge's entire life is extreme to match it's frigid environment; the only true insect living on the Antarctic continent, it spends most of its life frozen in the ice in a larval form, and once it emerges in its adult form it only lives a week to 10 days.
The researchers were impressed by its capacity to survive huge swings in temperatures, exposure to high levels of ultraviolet light and the other extreme conditions in Antarctica.
Given that, they were unprepared for the miniscule size of the genome of the insect.
"It's tiny. That was a huge surprise," says Joanna Kelly of Washington State University, a member of the team sequencing the genome of the 0.23-inch-long fly. "I was very impressed."
The minimalist nature of the midge's genome may be down to its extreme lifestyle in one of the harshest environments on Earth, the researchers report in Nature Communications.
"It has really taken the genome down to the bare bones and stripped it to a smaller size than was previously thought possible," Ohio State University entomologist David Denliger says. "It will be interesting to know if other extremophiles ticks, mites and other organisms that live in Antarctica also have really small genomes, or if this is unique to the midge. We don't know that yet."
In comparison with insects such as other flies and mosquitos, the Antarctic midge possesses a very economical genome, featuring very few repeated sequences or extra non-coding "junk DNA," the researchers said.
One kind of gene these midges possess in abundance is involved in transporting water into and out of their cells, which helps them survive in freezing conditions in which the larvae can lose up to 70 percent of their water.
"They look like dried-up little raisins, and when we pour water on them they plump up and go on their merry way," Denlinger says. "Being able to survive that extreme level of dehydration is one of the keys to surviving low temperatures. This midge has some mechanism that enables it to both be dehydrated and stay alive, with its cells functioning normally."