The Antarctic midge lives most of its life frozen, and it was just discovered that it has the smallest genome of all insects tested to date. The insect’s small genome may be a result of living in the extreme conditions of Antarctica.
The Antarctic midge, officially known as Belgica antarctica, is the only insect known to live in Antarctica. While Antarctica is used as a breeding ground by birds and seals, it has few animals that live there year round. Insects are abundant on all continents, however Antarctica has only one endemic species of insect, and it is the Antarctic midge. The midge is therefore used as a model for studying life that has adapted to extremely cold conditions, ultraviolet radiation and threat of dehydration. It has been termed an extremophile.
A study carried out by a team of scientists from a number of institutions analyzed the genome of the Antarctic midge. The research team leader was Johanna Kelley from Washington State University. The report on the study was published in the journal Nature Communications.
The Antarctic midge was shown to have a genome of only 99 megabases. A genome is the entire complement of all the DNA in all the chromosomes. A base is one molecule of DNA and a megabase is one million base pairs. Since a chromosome is comprised of two strands of DNA, the bases join together in the middle to form base pairs and this is what holds the two strands together. For comparison, the human genome is thought to be made up of three billion base pairs.
The Antarctic midge has a very low density of repeated DNA bases and a reduced intron length. A classical principle of DNA strands is exons contain coding information for proteins and introns and the sections of DNA in-between. Introns were said to contain “junk DNA” but that notion is currently changing with the development of epigenetics. The Antarctic midge seems to have a normal number of genes for an insect. They found an abundance of genes that were associated with development, metabolism regulation and responses to external stimulation. One of the interesting adaptations found in the Antarctic midge is messenger RNAs that encode heat shock proteins and enzymes that are usually produced under stress were found to exist at high levels all the time and not just as a response to a sudden stressful event. The authors of the study report interpreted the findings by suggesting that environmental extremes seem to affect the genome architecture more than the gene content.
The Antarctic midge larvae develop over two winters. While developing, the larvae experience high winds, high salt concentrations and intense ultraviolet radiation. When the adult emerges in the spring, it lives for about one week. The Antarctic midge is considered to be a fly but does not have wings and, therefore, does not fly. Since it cannot fly, it senses things that are close up. It has a few odor receptors to bring in sensory information. This insect crawls around to search for mates and food.
This very limited lifestyle may be the causal factor in the evolution of an extremely “economical” genome. Considering the fact that this insect spends most of its life frozen in Antarctica, a small, economical genome makes a lot of sense.
By Margaret Lutze