The Antarctic midge is the only insect found in Antarctica. That’s not a surprising thing given the harsh environmental conditions in the southern continent. What surprised scientists about this insect is its unusually streamlined genome. The wingless midge has the smallest insect genome ever sequenced. Its genome has only 99 million base pairs of nucleotides.
Antarctic midge’s genome is an adaptation to extreme environments
That means its DNA sequence is even smaller than those of body lice (105 million base pairs) and Strepsiptera, a winged parasite (108 million base pairs). By comparison, humans have more than three billion base pairs. Researchers said the small size of its DNA sequence could be explained by the Antarctic midge’s adaptation to the extreme environments.
The midge lives on the rocky outcrops of the Antarctica. For the most part of its two-years larval stage, the Antarctic midge remains frozen in ice. Its larval stage is divided into four sub-stages. At each sub-stage, the midge loses 50% of its body mass. Their adult life lasts only 7-10 days. And most of the adulthood is spent mating and laying eggs.
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The Antarctic midge has achieved this small genome by scrapping most of the “junk” DNA segments and elements that don’t make proteins. These “baggage” elements are found in most animal genomes. Previously, scientists believed that these elements served no purpose, but they were later found to play important roles in gene regulation.
David Denlinger, lead author of the study and professor of entomology at the Ohio State University, said that the lack of “baggage” elements could be the Antarctic midge’s evolutionary answer to surviving dry, cold conditions. Its genome has literally been reduced to bare bones. Researchers still don’t know whether other extremophiles living in the Antarctica also have small genomes or it’s unique to the midge.
Antarctic midge can survive even after losing up to 70% of its body water
The Antarctic midge’s genome may be small, but it contains the same number of genes as most other flies. Its tiny genome has 13,500 functional genes. Researchers also found aquaporins, a host of genes involved in water transportation into and out of cells, in the insect. These genes and proteins produced by them help the midge survive in harsh conditions.
Most insects die if they lose more than 20% of their body water. But the Antarctic midge can tolerate the loss of up to 70% of body water. Findings of the study appeared in the journal Nature Communications.