Drosophila

Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately (though less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit. They should not be confused with the Tephritidae, a related family, which are also called fruit flies (sometimes referred to as "true fruit flies"); tephritids feed primarily on unripe or ripe fruit, with many species being regarded as destructive agricultural pests, especially the Mediterranean fruit fly. One species of Drosophila in particular, D. melanogaster, has been heavily used in research in genetics and is a common model organism in developmental biology. Indeed, the terms "fruit fly" and "Drosophila" are often used synonymously with D. melanogaster in modern biological literature. The entire genus, however, contains more than 1,500 species and is very diverse in appearance, behavior, and breeding habitat.

Etymology
The term "Drosophila", meaning "dew-loving", is a modern scientific Latin adaptation from Greek words δρόσος, drósos, "dew", and φίλος, phílos, "loving" with the Latin feminine suffix -a.

Morphology
Drosophila are small flies, typically pale yellow to reddish brown to black, with red eyes. Many species, including the noted Hawaiian picture-wings, have distinct black patterns on the wings. The plumose (feathery) arista, bristling of the head and thorax, and wing venation are characters used to diagnose the family. Most are small, about 2–4 millimetres long, but some, especially many of the Hawaiian species, are larger than a house fly.

Habitat
Drosophila are found all around the world, with more species in the tropical regions. They can be found in deserts, tropical rainforest, cities, swamps, and alpine zones. Some northern species hibernate. Most species breed in various kinds of decaying plant and fungal material, including fruit, bark, slime fluxes, flowers, and mushrooms. The larvae of at least one species, D. suzukii, can also feed in fresh fruit and can sometimes be a pest. A few species have switched to being parasites or predators. Many species can be attracted to baits of fermented bananas or mushrooms, but others are not attracted to any kind of baits. Males may congregate at patches of suitable breeding substrate to compete for the females, or form leks, conducting courtship in an area separate from breeding sites.

Several Drosophila species, including D. melanogaster, D. immigrans, and D. simulans, are closely associated with humans, and are often referred to as domestic species. These and other species (D. subobscura, Zaprionus indianus  ) have been accidentally introduced around the world by human activities such as fruit transports.

Reproduction
Males of this genus are known to have the longest sperm cells of any organism on Earth, including one species, Drosophila bifurca, that has sperm 58 mm long. The cells are mostly tail, and are delivered to the females in tangled coils. The other members of the genus Drosophila also make relatively few giant sperm cells, with that of D. bifurca being the longest. D. melanogaster sperm cells are a more modest 1.8 mm long, although this is still about 300 times longer than a human sperm. Several species in the D. melanogaster species group are known to mate by traumatic insemination.

Drosophila vary widely in their reproductive capacity. Those such as D. melanogaster that breed in large, relatively rare resources have ovaries that mature 10–20 eggs at a time, so that they can be laid together on one site. Others that breed in more-abundant but less nutritious substrates, such as leaves, may only lay one egg per day. The eggs have one or more respiratory filaments near the anterior end; the tips of these extend above the surface and allow oxygen to reach the embryo. Larvae feed not on the vegetable matter itself but on the yeasts and microorganisms present on the decaying breeding substrate. Development time varies widely between species (between 7 and more than 60 days) and depends on the environmental factors such as temperature, breeding substrate, and crowding.

Laboratory–cultured animals
Drosophila melanogaster is a popular experimental animal because it is easily cultured in mass out of the wild, has a short generation time, and mutant animals are readily obtainable. In 1906, Thomas Hunt Morgan began his work on D. melanogaster and reported his first finding of a white (eyed) mutant in 1910 to the academic community. He was in search of a model organism to study genetic heredity and required a species that could randomly acquire genetic mutation that would visibly manifest as morphological changes in the adult animal. His work on Drosophila earned him the 1933 Nobel Prize in Medicine for identifying chromosomes as the vector of inheritance for genes. This and other Drosophila species are widely used in studies of genetics, embryogenesis, and other areas.

However, some species of Drosophila are difficult to culture in the laboratory, often because they breed on a single specific host in the wild. For some it can be done with particular recipes for rearing media, or by introducing chemicals such as sterols that are found in the natural host; for others it is (so far) impossible. In some cases, the larvae can develop on normal Drosophila lab medium but the female will not lay eggs; for these it is often simply a matter of putting in a small piece of the natural host to receive the eggs. The Drosophila Stock Center in San Diego maintains cultures of hundreds of species for researchers.

Predators
Drosophila are prey for many generalist predators such as robber flies. In Hawaii, the introduction of yellowjackets from the mainland United States has led to the decline of many of the large species. The larvae are preyed on by other fly larvae, staphylinid beetles, and ants.

Systematics


The genus Drosophila as currently defined is paraphyletic (see below) and contains 1,450 described species, while the estimated total number of species is estimated at thousands. The majority of the species are members of two subgenera: Drosophila (~1,100 species) and Sophophora (including D. (S.) melanogaster; ~330 species). The Hawaiian species of Drosophila (estimated to be more than 500, with ~380 species described) are sometimes recognized as a separate genus or subgenus, Idiomyia, but this is not widely accepted. About 250 species are part of the genus Scaptomyza, which arose from the Hawaiian Drosophila and later re-colonized continental areas.

Evidence from phylogenetic studies suggests that the following genera arose from within the genus Drosophila:
 * Liodrosophila Duda, 1922
 * Mycodrosophila Oldenburg, 1914
 * Samoaia Malloch, 1934
 * Scaptomyza Hardy, 1849
 * Zaprionus Coquillett, 1901
 * Zygothrica Wiedemann, 1830
 * Hirtodrosophila Duda, 1923 (position uncertain)

Several of the subgeneric and generic names are based on anagrams of Drosophila, including Dorsilopha, Lordiphosa, Siphlodora, Phloridosa and Psilodorha.


 * Further information: List of Drosophila species

Drosophila species genome project
Drosophila are extensively used as a model organism in genetics (including population genetics), cell-biology, biochemistry, and especially developmental biology. Therefore, extensive efforts are made to sequence drosphilid genomes. The genomes of the following species have been fully or partially sequenced so far:
 * Drosophila (Sophophora) melanogaster
 * Drosophila (Sophophora) simulans
 * Drosophila (Sophophora) sechellia
 * Drosophila (Sophophora) yakuba
 * Drosophila (Sophophora) erecta
 * Drosophila (Sophophora) ananassae
 * Drosophila (Sophophora) pseudoobscura
 * Drosophila (Sophophora) persimilis
 * Drosophila (Sophophora) willistoni
 * Drosophila (Drosophila) mojavensis
 * Drosophila (Drosophila) virilis
 * Drosophila (Drosophila) grimshawi

The data will be used for many purposes, including evolutionary genome comparisons. D. simulans and D. sechellia are sister species, and provide viable offspring when crossed, while D. melanogaster and D. simulans produce infertile hybrid offspring. The Drosophila genome is often compared with the genomes of more distantly related species such as the honeybee Apis mellifera or the mosquito Anopheles gambiae.

Curated data are available at FlyBase.