Drosophila

This article is about the entire genus. For the most commonly used laboratory species, see Drosophila melanogaster. For the type-subgenus, see Drosophila (subgenus). For a mushroom that once shared this name, see Psathyrella candolleana.

Drosophila
File:Drosophila repleta lateral.jpg
Drosophila repleta
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Diptera
Family:	Drosophilidae
Infratribe:	Drosophiliti
Genus:	Drosophila Fallén, 1823
Type species
Musca funebris Fabricius, 1787
Subgenera
Drosophila Sophophora Chusqueophila Dorsilopha Dudaica Phloridosa Psilodorha Siphlodora
Synonyms
Oinopota Kirby & Spence, 1815

Drosophila (/droʊˈsɒfələ/) is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or (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. 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

Side view of head showing characteristic bristles above the eye

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.

Life cycle and ecology

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 studied organism on Earth, including one species, Drosophila bifurca, that has a sperm 58 mm (2.3 in) 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 35 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. Numerous studies have shown that fruit flies lay eggs using an environmental circle. If fruit flies laid eggs at nighttime during which the environmental conditions were advantageous, the eggs could not be susceptible to desiccation from parasites. As a result, the offspring reproduced from these eggs would have greater fitness compared to offspring that were reproduced from eggs laid during the day. Since eggs are laid with a biological clock, Drosophila melanogaster become adaptive to their environmental cycles, which showed a major advantage.

The median lifespan is 35–45 days.

Life cycle of Drosophila

Egg

Larva

Pupae (brown examples are older than the white ones)

Adult Drosophila melanogaster

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 Species Stock Center in San Diego maintains cultures of hundreds of species for researchers.

Microbiome

Like other metazoans Drosophila is associated with various bacteria in its gut. The fly gut microbiota or microbiome seems to have a central influence on Drosophila fitness and life history characteristics. The microbiota in the gut of Drosophila represents an active current research field.

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

immigrans-tripunctata radiation  D. quadrilineata species group  Samoaia  Zaprionus  D. tumiditarsus species group  Liodrosophila  Dichaetophora  Hirtodrosophila  Mycodrosophila  Paramycodrosophila  virilis-repleta radiation (in part)  subgenus Siphlodora  virilis-repleta radiation (in part)  Hawaiian Drosophila  Scaptomyza  D. polychaeta species group  Dorsilopha  Old World Sophophora  New World Sophophora  Lordiphosa  Hirtodrosophila duncani

D. setosimentum, a species of Hawaiian picture-wing fly

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 sequenced:

• 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 have been 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.

The modEncode consortium is currently sequencing 8 more Drosophila genomes, and even more genomes are being sequenced by the i5K consortium.

Curated data are available at FlyBase.

External links

• Fly Base FlyBase is a comprehensive database for information on the genetics and molecular biology of Drosophila. It includes data from the Drosophila Genome Projects and data curated from the literature.
• Berkeley Drosophila Genome Project
• Annual Drosophila Research Conference
• AAA: Assembly, Alignment and Annotation of 12 Drosophila species
• UCSC Genome browser
• TaxoDros: The database on Taxonomy of Drosophilidae
• UC San Diego Drosophila Stock Center breeds hundreds of species and supplies them to researchers
• FlyMine is an integrated database of genomic, expression and protein data for Drosophila
• The Drosophila Virtual library is library of Drosophila on web
• Drosophila Melanogaster contains further information.
• C-CAMP Fly facility - In India microinjection service for the generation of transgenic lines, Screening Platforms, Drosophila strain development