Belgica antarctica, the Antarctic midge, is a species of flightless midge, endemic to the continent of Antarctica. At 2–6 mm (0.08–0.2 in) long, it is the largest purely terrestrial animal native to the continent. It also has the smallest known insect genome as of 2014, with only 99 million base pairs of nucleotides and about 13500 genes. It is the only insect that can survive year-round in Antarctica.
The first specimens of Belgica antarctica were collected on the Belgian Antarctic Expedition (1897–1899).[2] During this expedition organized by the Belgian Government, Romanian biologist Emil Racoviță collected, among other specimens, a flightless midge and its larvae.[2] Based on these specimens, the Belgian doctor and entomologist, Jean-Charles Jacobs, described Belgica antarctica Jacobs, 1900.[3] Jacobs named the new genus and species of insect after the location where it was collected off the Antarctic Peninsula, "canal de la Belgica antarctica" (Belgian Strait)[3] (now called Gerlache Strait), which in turn was named after the expedition's stead-yacht, SY Belgica.[4]
The flightlessness of B. antarctica may be an adaptation to prevent wind from blowing it into inhospitable areas.[6] It can survive freezing, but though local air temperatures may reach as low as −40 °C, this insect cannot survive temperatures below −15 °C. This is comparatively milder than other cold-adapted insects. The reason for this relatively low freezing tolerance is due to thermal buffering: just burrowing at a depth of 1 cm, temperature is stable between 0 and −2 °C for 10 months out of 12, and it seldom goes lower than −7 °C all year round. Ice and snow cover also helps keep the temperature stable.[7] Freezing tolerance is enhanced by cold hardening.[7]
To adapt to the cold temperatures, B. antarctica accumulates trehalose, glucose, and erythritol. These compounds help the insect survive freezing by reducing the amount of ice that forms within the body. They also stabilize proteins and membranes, binding to them by means of hydrogen bonds. Heat shock proteins also help the tolerance to both high and low temperatures.[8]
Belgica antarctica not only tolerates, but also requires a freezing climate to survive: exposure of larvae to such mild temperatures as 10 °C is enough to kill them within a week.[7] Exposure to temperatures of 30 °C kills individuals in a few hours.[8] It can, however, resist partial desiccation, surviving the loss of up to 70% of body water.[8]
B. antarctica spends most of its two-year lifecycle in four larval stages. Overwintering may occur in any instar. Terrestrial algae (particularly Prasiola crispa), moss, organic detritus, and microorganisms provide the food for the larval stage. The adults emerge in the spring and summer and live no more than 10 days; females mate in their first day of life and a few days later release eggs. The female secretes a jelly on the eggs that acts as a blanket of antifreeze, stops them from dehydrating, and acts as a food source once they hatch.
Mating occurs in large groups of males, analogous to swarms of winged midges.[7]
As of 2014, B. antarctica has the smallest insect genome known, at 99 Mbp and 13 500 genes.[9] Although the total amount of coding DNA is similar to that of other Diptera (19 Mbp), its fraction is much higher due to the extreme reduction in some types of non-coding DNA. Intron size has been reduced, while transposable elements are almost absent.[10]
^Usher, Michael B.; Edwards, Marion (1984). "A dipteran from south of the Antarctic Circle: Belgica antarctica (Chironomidae) with a description of its larva". Biological Journal of the Linnean Society. 23 (1): 19–31. doi:10.1111/j.1095-8312.1984.tb00803.x.
^ abcRobert Michaud, M.; Benoit, J. B.; Lopez-Martinez, G.; Elnitsky, M. A.; Lee, R. E.; Denlinger, D. L. (2008). "Metabolomics reveals unique and shared metabolic changes in response to heat shock, freezing and desiccation in the Antarctic midge, Belgica antarctica". Journal of Insect Physiology. 54 (4): 645–655. doi:10.1016/j.jinsphys.2008.01.003. PMID18313070.
Rübsaamen, Ew. H. (1906). "Chironomidæ". Zoologie: Insectes. Résultats du voyage du S.Y. Belgica en 1897-1898-1899. Anvers: J.-E. Buschmann. pp. 77–83; Pl. 4, Figs. 2, 4–7; Pl. V, Figs. 9–19.
