Washington: The Antarctic midge - a small, wingless fly - with only 99 million base pairs of nucleotides has the smallest insect genome ever sequenced, scientists say.
The small size of the genome can probably be explained by the midge`s adaptation to its extreme living environment, researchers said.
The midge spends most of its two-year larval stage frozen in the Antarctic ice. Upon adulthood, the insects spend seven to 10 days mating and laying eggs, and then they die.
Its genome contains only 99 million base pairs of nucleotides, making it smaller than other tiny reported genomes for the body louse (105 million base pairs) and the winged parasite Strepsiptera (108 million base pairs), as well as the genomes of three other members of the midge family.
The midge genome lacks many of the segments of DNA and other repeat elements that don`t make proteins, which are found in most animal genomes.
The lack of such "baggage" in the genome could be an evolutionary answer to surviving the cold, dry conditions of Antarctica, said senior author David Denlinger, Distinguished Professor of entomology and of evolution, ecology and organismal biology at The Ohio State University.
"It has really taken the genome down to the bare bones and stripped it to a smaller size than was previously thought possible," Denlinger said.
"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," Denlinger said.
The midge genome is small in architecture but not in the number of genes, the researchers noted: The Antarctic midge genome, like genomes of other flies, contains about 13,500 functional genes.
The research also found a host of genes called aquaporins, which are involved in water transport into and out of cells. These genes and the proteins they make are also players in the midge`s survival in Antarctica.
Most insects can survive losing about 20 per cent of the water in their bodies` cells, but these midges tolerate a loss of up to 70 per cent of their water.
"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," Denlinger said.
The research is published in the journal Nature Communications.
