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''Belgica antarctica'', the Antarctic midge, is a species of flightless
midge A midge is any small fly, including species in several families of non- mosquito Nematoceran Diptera. Midges are found (seasonally or otherwise) on practically every land area outside permanently arid deserts and the frigid zones. Some mi ...
,
endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...
to the continent of
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
. At long, it is the largest purely
terrestrial animal Terrestrial animals are animals that live predominantly or entirely on land (e.g. cats, dogs, ants, spiders), as compared with aquatic animals, which live predominantly or entirely in the water (e.g. fish, lobsters, octopuses), and amphibian ...
native to the continent. It also has the smallest known insect
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ...
as of 2014, with only 99 million base pairs of
nucleotides Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules with ...
and about genes. It is the only insect that can survive year-round in Antarctica.


Tolerance to extreme conditions

The flightlessness of ''B. antarctica'' may be an
adaptation In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
to prevent wind from blowing it into inhospitable areas. 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. Freezing tolerance is enhanced by
cold hardening Cold hardening is the physiological and biochemical process by which an organism prepares for cold weather. Plants Plants in temperate and polar regions adapt to winter and sub zero temperatures by relocating nutrients from leaves and shoots to ...
. To adapt to the cold temperatures, ''B. antarctica'' accumulates
trehalose Trehalose (from Turkish '' tıgala'' – a sugar derived from insect cocoons + -ose) is a sugar consisting of two molecules of glucose. It is also known as mycose or tremalose. Some bacteria, fungi, plants and invertebrate animals synthesize it ...
,
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
, and
erythritol Erythritol is an organic compound, a four-carbon sugar alcohol (or polyol) with no optical activity, used as a food additive and sugar substitute. It is naturally occurring. It can be made from corn using enzymes and fermentation. Its formula is ...
. These compounds help the insect survive freezing by reducing the amount of ice that forms within the body. They also stabilize
proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
and
membranes A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. Bi ...
, binding to them by means of
hydrogen bonds In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a l ...
. Heat shock proteins also help the tolerance to both high and low temperatures. ''B. 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. Exposure to temperatures of 30 °C kills individuals in a few hours. It can, however, resist partial
desiccation Desiccation () is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container. ...
, surviving the loss of up to 70% of body water.


Lifecycle

''B. antarctica'' spends most of its two-year lifecycle in four larval stages. Overwintering may occur in any
instar An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ...
. Terrestrial algae (particularly '' Prasiola crispa''), moss, organic
detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts comm ...
, 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.


Genome

As of 2014, ''B. antarctica'' has the smallest insect genome known, at 99 Mbp and 13 500 genes. Although the total amount of
coding DNA The coding region of a gene, also known as the coding sequence (CDS), is the portion of a gene's DNA or RNA that codes for protein. Studying the length, composition, regulation, splicing, structures, and functions of coding regions compared to n ...
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 A transposable element (TE, transposon, or jumping gene) is a nucleic acid sequence in DNA that can change its position within a genome, sometimes creating or reversing mutations and altering the cell's genetic identity and genome size. Trans ...
are almost absent.


See also

* '' Gynaephora groenlandica'', a species of Arctic moth whose larvae can survive temperatures below –60 °C * ''
Belgian Antarctic Expedition The Belgian Antarctic Expedition of 1897–1899 was the first expedition to winter in the Antarctic region. Led by Adrien de Gerlache de Gomery aboard the RV ''Belgica'', it was the first Belgian Antarctic expedition and is considered the firs ...
''


References


Further reading

* * * * *


External links


Other bugs that live in Antarctica
{{Taxonbar, from=Q136577 Fauna of Antarctica Insects described in 1900 A Insects of Antarctica Wingless Diptera Taxa named by Jean-Charles Jacobs