Common Fruit Fly

Appearance

Wildtype fruit flies have brick red eyes, are yellow-brown in color, and have transverse black rings across their abdomen. They exhibit sexual dimorphism: females are about 2.5 millimeters long; males are slightly smaller and the back of their bodies is darker. Males are easily distinguished from females based on color differences, with a distinct black patch at the abdomen, less noticeable in recently emerged flies, and the sexcombs. Furthermore, males have a cluster of spiky hairs surrounding the reproducing parts used to attach to the female during mating. There are extensive images at FlyBase.

Behavior

The "D. melanogaster" lifespan is about 30 days at 29 °C.

The developmental period for "Drosophila melanogaster" varies with temperature, as with many ectothermic species. The shortest development time, 7 days, is achieved at 28 °C. Development times increase at higher temperatures due to heat stress. Under ideal conditions, the development time at 25 °C is 8.5 days, at 18 °C it takes 19 days and at 12 °C it takes over 50 days. Under crowded conditions, development time increases, while the emerging flies are smaller. Females lay some 400 eggs, about five at a time, into rotting fruit or other suitable material such as decaying mushrooms and sap fluxes. The eggs, which are about 0.5 millimetres long, hatch after 12–15 hours. The resulting larvae grow for about 4 days while molting twice, at about 24 and 48 h after hatching. During this time, they feed on the microorganisms that decompose the fruit, as well as on the sugar of the fruit itself. Then the larvae encapsulate in the puparium and undergo a four-day-long metamorphosis, after which the adults eclose.

Females become receptive to courting males at about 8–12 hours after emergence. Males perform a sequence of five behavioral patterns to court females. First, males orient themselves while playing a courtship song by horizontally extending and vibrating their wings. Soon after, the male positions itself at the rear of the female's abdomen in a low posture to tap and lick the female genitalia. Finally, the male curls its abdomen, and attempts copulation. Females can reject males by moving away, kicking and extruding their ovipositor. Copulation lasts around 15–20 minutes, during which males transfer a few hundred very long sperm cells in seminal fluid to the female. Females store the sperm in a tubular receptacle and in two mushroom-shaped spermathecae, sperm from multiple matings compete for fertilization. A last male precedence is believed to exist in which the last male to mate with a female sires approximately 80% of her offspring. This precedence was found to occur through displacement and incapacitation. The displacement is attributed to sperm handling by the female fly as multiple matings are conducted and is most significant during the first 1–2 days after copulation. Displacement from the seminal receptacle is more significant than displacement from the spermathecae. Incapacitation of first male sperm by second male sperm becomes significant 2–7 days after copulation. The seminal fluid of the second male is believed to be responsible for this incapacitation mechanism which takes effect before fertilization occurs. The delay in effectiveness of the incapacitation mechanism is believed to be a protective mechanism that prevents a male fly from incapacitating its own sperm should it mate with the same female fly repetitively.In 1971, Ron Konopka and Seymour Benzer published "Clock mutants of "Drosophila melanogaster"", a paper describing the first mutations that affected an animal's behavior. Wild-type flies show an activity rhythm with a frequency of about a day. They found mutants with faster and slower rhythms as well as broken rhythms—flies that move and rest in random spurts. Work over the following 30 years has shown that these mutations affect a group of genes and their products that comprise a biochemical or biological clock. This clock is found in a wide range of fly cells, but the clock-bearing cells that control activity are several dozen neurons in the fly's central brain.

Since then, Benzer and others have used behavioral screens to isolate genes involved in vision, olfaction, audition, learning/memory, courtship, pain and other processes, such as longevity.

The first learning and memory mutants were isolated by William "Chip" Quinn while in Benzer's lab, and were eventually shown to encode components of an intracellular signaling pathway involving cyclic AMP, protein kinase A and a transcription factor known as CREB. These molecules were shown to be also involved in synaptic plasticity in "Aplysia" and mammals.

Male flies sing to the females during courtship using their wing to generate sound, and some of the genetics of sexual behavior have been characterized. In particular, the fruitless gene has several different splice forms, and male flies expressing female splice forms have female-like behavior and vice-versa.

Furthermore, "Drosophila" has been used in neuropharmacological research, including studies of cocaine and alcohol consumption.

Reproduction

The "D. melanogaster" lifespan is about 30 days at 29 °C.

The developmental period for "Drosophila melanogaster" varies with temperature, as with many ectothermic species. The shortest development time, 7 days, is achieved at 28 °C. Development times increase at higher temperatures due to heat stress. Under ideal conditions, the development time at 25 °C is 8.5 days, at 18 °C it takes 19 days and at 12 °C it takes over 50 days. Under crowded conditions, development time increases, while the emerging flies are smaller. Females lay some 400 eggs, about five at a time, into rotting fruit or other suitable material such as decaying mushrooms and sap fluxes. The eggs, which are about 0.5 millimetres long, hatch after 12–15 hours. The resulting larvae grow for about 4 days while molting twice, at about 24 and 48 h after hatching. During this time, they feed on the microorganisms that decompose the fruit, as well as on the sugar of the fruit itself. Then the larvae encapsulate in the puparium and undergo a four-day-long metamorphosis, after which the adults eclose.

Females become receptive to courting males at about 8–12 hours after emergence. Males perform a sequence of five behavioral patterns to court females. First, males orient themselves while playing a courtship song by horizontally extending and vibrating their wings. Soon after, the male positions itself at the rear of the female's abdomen in a low posture to tap and lick the female genitalia. Finally, the male curls its abdomen, and attempts copulation. Females can reject males by moving away, kicking and extruding their ovipositor. Copulation lasts around 15–20 minutes, during which males transfer a few hundred very long sperm cells in seminal fluid to the female. Females store the sperm in a tubular receptacle and in two mushroom-shaped spermathecae, sperm from multiple matings compete for fertilization. A last male precedence is believed to exist in which the last male to mate with a female sires approximately 80% of her offspring. This precedence was found to occur through displacement and incapacitation. The displacement is attributed to sperm handling by the female fly as multiple matings are conducted and is most significant during the first 1–2 days after copulation. Displacement from the seminal receptacle is more significant than displacement from the spermathecae. Incapacitation of first male sperm by second male sperm becomes significant 2–7 days after copulation. The seminal fluid of the second male is believed to be responsible for this incapacitation mechanism which takes effect before fertilization occurs. The delay in effectiveness of the incapacitation mechanism is believed to be a protective mechanism that prevents a male fly from incapacitating its own sperm should it mate with the same female fly repetitively.

Evolution

"Drosophila melanogaster" was among the first organisms used for genetic analysis, and today it is one of the most widely used and genetically best-known of all eukaryotic organisms. All organisms use common genetic systems; therefore, comprehending processes such as transcription and replication in fruit flies helps in understanding these processes in other eukaryotes, including humans.

Charles W. Woodworth is credited with being the first to breed "Drosophila" in quantity and for suggesting to W. E. Castle that they might be used for genetic research during his time at Harvard University.

Thomas Hunt Morgan began using fruit flies in experimental studies of heredity at Columbia University in 1910. His laboratory was located on the top floor of Schermerhorn Hall, which became known as the Fly Room. The Fly Room was cramped with eight desks, each occupied by students and their experiments. They started off experiments using milk bottles to rear the fruit flies and handheld lenses for observing their traits. The lenses were later replaced by microscopes, which enhanced their observations. The Fly Room was the source of some of the most important research in the history of biology. Morgan and his students eventually elucidated many basic principles of heredity, including sex-linked inheritance, epistasis, multiple alleles, and gene mapping.

"Thomas Hunt Morgan and colleagues extended Mendel's work by describing X-linked inheritance and by showing that genes located on the same chromosome do not show independent assortment. Studies of X-linked traits helped confirm that genes are found on chromosomes, while studies of linked traits led to the first maps showing the locations of genetic loci on chromosomes". The first maps of "Drosophila" chromosomes were completed by Alfred Sturtevant.