PULLMAN, Wash.--Few animals can boast of being as tough as the Antarctic midge. Its larvae develop over not one but two Antarctic winters, losing nearly half their body mass each time. It endures high winds, salt, and intense ultraviolet radiation. As an adult, the midge gets by without wings and lives for only a week or so before starting its life cycle all over again.
And as Joanna Kelley has learned, it does this with the smallest insect genome sequenced so far.
"It's tiny," said Kelley, a Washington State University assistant professor, who recently sequenced and analyzed the genome with colleagues around the U.S. "That was a huge surprise. I was very impressed."
Writing in the online journal Nature Communications, Kelley and her fellow researchers say the midge genome has only 99 million base pairs, the building blocks of their DNA. By comparison, the human genome has 3.2 billion base pairs.
"We suspect that it's somehow an adaptation to the extreme environment," says Kelley. "And it opens up a lot of interesting hypotheses to hopefully test by sequencing additional Antarctic organisms or sub-Antarctic organisms, because there are other flies, or Diptera, on some of the sub-Antarctic islands. We're really interested to see whether or not they have similar genomes."
Living on rock outcrops on the Antarctic Peninsula, the midge is the only insect and fully terrestrial animal endemic to the continent. In looking at its genes and comparing them with their known functions in other animals, Kelley and her colleagues found an abundance of genes geared towards regulation and developmental processes.
On the other hand, it has few odorant receptors. This could be because it rarely ventures far, having no wings, and doesn't need to detect things much further than it can walk.
Compared to other insects, like mosquitoes and other flies, the midge has an extremely economical genome, with very few repeated genetic sequences and shorter stretches of DNA, called introns, separating coding regions of the genome.
Overall, the genome, said Kelley, "opens up a lot of questions for me about genome evolution and I'm looking at other related organisms to try and get at that question. What allows or inhibits a genome from being very large or small and what are the consequences of that?
"It's a pretty exciting fly."
Kelley's colleagues on the genome project are affiliated with The Ohio State University, Stanford University, the Institut des Sciences de l'Evolution in France, the University of Florida, Texas A&M University and Miami University.