Drosophila


Drosophila, from Ancient Greek δρόσος, meaning "dew", and φίλος, meaning "loving", is a genus of fly, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or 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 ; 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, Drosophila 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".

Morphology

Drosophila species are small flies, typically pale yellow to reddish brown to black, with red eyes. When the eyes are removed, the brain is revealed. Drosophila brain structure and function develop and age significantly from larval to adult stage. Developing brain structures make these flies a prime candidate for neuro-genetic research. According to a study published in Nature in October 2024, by the scientists examining the brain of an adult female Drosophila, the shape and location of each of its 130,000 neurons and 50 million synapses were identified. In this study, the most detailed analysis ever conducted on the brain of an adult animal is represented. Many species, including the noted Hawaiian picture-wings, have distinct black patterns on the wings. The plumose arista, bristling of the head and thorax, and wing venation are characters used to diagnose the family. Most are small, about long, but some, especially many of the Hawaiian species, are larger than a house fly.

Evolution

Detoxification mechanisms

Environmental challenge by natural toxins helped to prepare Drosophilae to detox DDT, by shaping the glutathione S-transferase mechanism that metabolizes both.

Selection

The Drosophila genome is subject to a high degree of selection, especially unusually widespread negative selection compared to other taxa. A majority of the genome is under selection of some sort, and a supermajority of this is occurring in non-coding DNA.
Effective population size has been credibly suggested to positively correlate with the effect size of both negative and positive selection. Recombination is likely to be a significant source of diversity. There is evidence that crossover is positively correlated with polymorphism in Drosophila populations.

Biology

Habitat

Drosophila species are found all around the world, with more species in the tropical regions. Drosophila made their way to the Hawaiian Islands and radiated into over 800 species. They can be found in deserts, tropical rainforest, cities, swamps, and alpine zones. Some northern species hibernate. The northern species D. montana is the best cold-adapted, and is primarily found at high latitudes or high altitudes. Most species breed in various kinds of decaying plant and fungal material, including fruit, bark, slime fluxes, flowers, and mushrooms. Drosophila species that are fruit-breeding are attracted to various products of fermentation, especially ethanol and methanol. Fruits exploited by Drosophila species include those with a high pectin concentration, which is an indicator of how much alcohol will be produced during fermentation. Citrus, morinda, apples, pears, plums, and apricots belong into this category.
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 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, D. bifurca, that has sperm cells that are long. The cells mostly consist of a long, thread-like 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 species 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 and depends on the environmental factors such as temperature, breeding substrate, and crowding.
Fruit flies lay eggs in response to environmental cycles. Eggs laid at a time during which likelihood of survival is greater than in eggs laid at other times yield more larvae than eggs that were laid at those times. Ceteris paribus, the habit of laying eggs at this 'advantageous' time would yield more surviving offspring, and more grandchildren, than the habit of laying eggs during other times. This differential reproductive success would cause D. melanogaster to adapt to environmental cycles, because this behavior has a major reproductive advantage.
Their median lifespan is 35–45 days.

Aging

accumulates in Drosophila intestinal stem cells with age. Deficiencies in the Drosophila DNA damage response, including deficiencies in expression of genes involved in DNA damage repair, accelerates intestinal stem cell aging. Sharpless and Depinho reviewed evidence that stem cells undergo intrinsic aging and speculated that stem cells grow old, in part, as a result of DNA damage.

Mating systems

Courtship behavior

The following is based on D. simulans and D. melanogaster.
Courtship behavior of male Drosophila is an attractive behaviour. Females respond via their perception of the behavior portrayed by the male. Male and female Drosophila use a variety of sensory cues to initiate and assess courtship readiness of a potential mate. The cues include the following behaviours: positioning, pheromone secretion, following females, making tapping sounds with legs, singing, wing spreading, creating wing vibrations, genitalia licking, bending the stomach, attempt to copulate, and the copulatory act itself. The songs of D. melanogaster and D. simulans have been studied extensively. These luring songs are sinusoidal in nature and vary within and between species.
The courtship behavior of Dr. melanogaster has also been assessed for sex-related genes, which have been implicated in courtship behavior in both the male and female. Recent experiments explore the role of fruitless and doublesex, a group of sex-behaviour linked genes.
The fruitless gene in Drosophila helps regulate the network for male courtship behavior; when a mutation to this gene occurs altered same sex sexual behavior in males is observed. Male Drosophila with the fru mutation direct their courtship towards other males as opposed to typical courtship, which would be directed towards females. Loss of the fru mutation leads back to the typical courtship behavior.

Pheromones

A novel class of pheromones was found to be conserved across the subgenus Drosophila in 11 desert dwelling species. These pheromones are triacylglycerides that are secreted exclusively by males from their ejaculatory bulb and transferred to females during mating. The function of the pheromones is to make the females unattractive to subsequent suitors and thus inhibit courtship by other males.

Polyandry

The following section is based on the following Drosophila species: D. serrata, D. pseudoobscura, D. melanogaster, and D. neotestacea. Polyandry is a prominent mating system among Drosophila. Females mating with multiple sex partners has been a beneficial mating strategy for Drosophila. The benefits include both pre and post copulatory mating. Pre-copulatory strategies are the behaviours associated with mate choice and the genetic contributions, such as production of gametes, that are exhibited by both male and female Drosophila regarding mate choice. Post copulatory strategies include sperm competition, mating frequency, and sex-ratio meiotic drive.
These lists are not inclusive. Polyandry among the D. pseudoobscura in North America vary in their number of mating partners. There is a connection between the number of time females choose to mate and chromosomal variants of the third chromosome. It is believed that the presence of the inverted polymorphism is why re-mating by females occurs. The stability of these polymorphisms may be related to the sex-ratio meiotic drive.
However, for D. subobscura, the main mating system is monandry, not normally seen in ''Drosophila.''