Drosophila subobscura | |
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Five anatomical images of a Drosophila subobscura (male) on a rotting squash, located near Christchurch Park, Ipswich | |
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Species group: | obscura |
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Species: | D. subobscura |
Binomial name | |
Drosophila subobscura Collin, 1936 | |
Drosophila subobscura is a species of fruit fly in the family Drosophilidae. Originally found around the Mediterranean, it has spread to most of Europe and the Near East. It has been introduced into the west coasts of Canada, the United States, and Chile. Its closest relative is Drosophila madeirensis , found in the Madeira Islands, followed by D. guanche , found in the Canary Islands. These three species form the D. subobscura species subgroup. When they mate, males and females perform an elaborate courtship dance, in which the female can either turn away to end the mating ritual, or stick out her proboscis in response to the male's, allowing copulation to proceed. D. subobscura has been regarded as a model organism for its use in evolutionary-biological studies.
Both wild type and laboratory-reared individuals of D. subobscura are brown, with clear wings, yellow halters, yellowish legs, and red eyes. They do not exhibit sexual size dimorphism; the males and females are about 2 mm (0.08 in) long. The males have a brown antenna, grey pollinose, and brown dorsal surface of the thorax. The tergum (dorsal area excluding the head) is dark brown. There are three tarsal segments on the fore legs. The first segment is the longest and contains the proximal comb, which has 7-12 teeth. The second segment contains the distal comb, which has 10-13 teeth. The females share the same characteristics as the males, except in respect to tarsal combs. The eggs are only half the length of those of the closely related D. obscura species. Its larvae and pupa are of the usual drosophilid type. [1]
The arista (bristles arising from the antennae) of D. subobscura contain 6-8 branches, with 1-2 of those branches below the terminal fork. The species has a brown antenna with grey pollinosity that is approximately the same color as the rest of the head-capsule. The front of the antenna is dark brown and matte, without any pollinosity except on the frontal triangle and fronto-orbital plates, both of which are shiny and slightly pollinose. The carina (tracheal cartilage that divides the two bronchi) of the fly is rounded, widening below, and the face is a paler brown color with grey pollinosoty. The genae is brown with heavy, grey pollinosity. The ocelli (small or 'simple' eyes of an insect) are the same color as the eyes. [1]
The dorsa of the thorax is brown with grey pollinose. There appear to be no traces of any longitudinal stripes or lines upon it. [1] The wings are colorless. Their membrane never folds nor crumples, but instead expands and displays intricate venation. [1] [2]
The legs of D. subobscura are a yellowish color. The combs of the teeth are each aligned on the longitudinal axis of the first and second tarsal segments of the fore legs. The proximal comb, identified as the comb of the first segment, has 7-12 teeth and is about half as long as the segment itself. Teeth on the distal end of the segment are slightly longer than the segment. The first tarsal segment is slightly longer than both the second and third segments, but shorter than their combined length. The abdomen has tergites that are uniformly dark brown, but shiny in some lights. Other lights reveal a grey pollinosity appearance. [1]
The upper reclinate fronto-orbital bristles are long, the middle reclinate bristles are short, and the lower proclinate bristles are medium in length. Proportionally, the listed bristles lengths can be characterized in a 4:2:3 fashion. The ocellar, post-vertical, and inner and outer vertical bristles are all about the same length as the upper reclinate fronto-orbital bristles. The bristle behind the vibrissa is less than half the length of the upper reclinate fronto-orbital bristles. The species also has two pairs of dorso-central bristles, which contain 8-10 rows of acrostichal hairs. No acrostichal bristles are seen to have developed in the species. The anterior scutella bristles are parallel to each other. The anterior sternopleural bristles are shorter than the posterior ones. The wings have costal bristles. The pre-apical tibial and apical tibial bristles of the legs are not exceptionally long. [1]
D. subobscura are found to be unusual among the Drosophila genus, because they are monandrous (females only mate one at a time). [3] [4] Additionally, unlike the rest of the Drosophila genus, D. subobscura do not mate in the absence of light [5] [6] nor do they produce courtship songs by wing vibration. [7] A study published in 2017 revealed that the difference in courtship behavior between D. subobscura and D. melanogaster (in particular, the D. subobscura's nuptial gift transfer behavior) could be potentially due to the optogenetic activation of a distinct neural circuit that differs in both flies. [8]
In 1933, A. H. Sturtevant captured a species of Drosophila in England. When Sturtevant submitted the captured specimens to J. E. Collin of Newmarket, Collin initially misidentified the species as D. obscura. Three years later, the first description of D. subobscura appeared in an addendum to Gordon's paper through a short note written by Collin. In the note, Collin compared both sexes of D. subobscura and differentiated them as a separate species from D. obscura, their nearest related species. Collin's description, considered incomplete but necessary to validate the D. subobscura name, was followed up with a more complete description by Dr. James Smart. [9] [10] [1]
In 1942, A. H. Sturtevant founded the obscura group, which initially consisted of the affinis and obscura species groups. [11] The obscura group falls under the subgenus Sophophora . The obscura species group currently contains 6 subgroups, listed alphabetically: affinis,microlabis,obscura,pseudoobscura,subobscura, and sinobscura.D. subobscura belongs to the subobscura subgroup, along with the closely related Drosophila guanche and Drosophila madeirensis . [12]
In experimental trials, D. subobscura does not breed with any other species of obscura, except D. madeirensis, a species also in the subobscura subgroup. When crossed, sterile males and fertile female hybrids are formed. [13] As of March 2019, the first long-read sequencing of D. subobscura's genome has been presented, showing that evolution of its genome structure is indirectly driven by the effects of suppressing recombination of genetic inversions. This suppressive effect maintains various sets of adaptive alleles together in the midst of gene flow. [14]
When Collin identified Sturtevant's captured species as D. subobscura in 1933, the name was coined as a manuscript name. The species was then bred at the Department of Biometry in University College in London to be genetically experimented on. Here, one paper that resulted from this experimental work in London referred to the tested species as Collin's coined manuscript name, D. subobscura, and was referred to as such moving forward. During this time, involved parties knew that D. subobscura was simply a manuscript name, thus creating anticipation that Collin would publish a description of the species and consequently validate the name. Although Collin did not publish the anticipated description of the species, in 1936, he contributed a note in the addendum of a paper published by Gordon that same year. The note outlines a diagnosis of the sexes and differentiation of the species from D. obscura and attributes the D. subobscura name to Collin. Thus, the name “D. subobscura Collin” dates from 1936, because none of the papers that come before it include a description of the given species that would have satisfied nomenclature rules. Therefore, prior to the addendum in Gordon's paper in 1936, the D. subobscura name used in published works must be regarded as a manuscript name. In 1938, two years after Gordon's paper, Dr. Eugéne Séguy had discovered a new species of Drosophila in Kenya, naming it D. subobscura. Though this D. subobscura was recorded in the 1938 Zoological Record , the “D. subobscura Collin” name has not appeared in the Zoological Record as a new species, yet. [1] [15] [16] [17]
D. subobscura is widely distributed in Europe, from Scandinavia south to the Mediterranean, and in North Africa and the Middle East as far east as Iran. [18] Its distribution spans over thirty latitudinal degrees, with its most dense populations residing in the western Palaeartic realm. [19] Introduced populations of D. subobscura are found in the west coasts of Canada, the United States, and Chile. [20]
D. subobscura was first discovered in the Americas (southern Chile) in February 1978. [21] D. subobscura was later found in La Serena, Chile, in the summer of 1979; [22] Punta Arenas, Chile, in January 1981; San Carlos de Bariloche, Argentina, in November 1981; and then Mar de Plata, Argentina, in 1984. In 1982, D. subobscura was discovered in North America in the city of Port Townsend, Washington, followed by the surrounding northern and southern areas, from Vancouver B.C. to Oregon. In fall 1983, D. subobscura was found in the Central Valley, Davis, and El Rio areas of California. [23]
There has been recent speculation about D. subobscura colonization in western North America being a more modern-event. The origin of the North and South America colonizers remains unknown, but evidence reveals that they derive from the original, Palearctic populations. [20]
D. subobscura is mainly found in open fields or forest fringes. [24] Decreases in light and temperature induce locomotion activity in D. subobscura towards areas outside of the forest. [25] The genome of some Greek populations of D. subobscura has shown evidence of microgeographic variation, prompting a possibility that the species exhibits habitat choice. [26]
However, no evidence has been found to show that D. subobscura exhibits individual habitat choice, aligning with the fact that its well-studied inversion polymorphism is relatively inflexible and slow to respond to the environment. Additionally, individuals do not exhibit much preference for different times of the day; even then, there remains some evidence to suggest that the species displays feeding and breeding site fidelity, as individuals were shown to return to familiar baits. [27]
D. subobscura is monandrous, a behavior not usually seen among Drosophila. [28] Visual stimuli dictate courtship behavior. [29] D. subobscura do not mate in the dark [30] and do not produce a courtship song via wing vibrations like other species of Dipterans. [31] Instead, the lone male repeatedly “scissors” its wings, an activity augmented in the presence of other flies. This behavior indicates that the male is looking to court a female. When a female appears, the male taps her with his own front legs. The male then stands in front and directly faces the female to stick out his proboscis. The male and female then start to “dance”, as the female rapidly sidesteps, while the male tries to keep himself directly facing the female. During the dance, the male's wings are usually raised and extended. Sometimes, mounting can occur without a dance taking place prior. At this point, the female has two options: she can either end the dance, without mating, by turning away from the male and leaving, or she can stand still, extend her own proboscis, and invite the male to mount her by parting her wings. In the latter behavior, the male stretches its wings sideways and swings behind the female to mount her. The male and female probosces may or may not touch beforehand. [29] Additionally, unique to just D. subobscura among the other species in its subgroup, males will attempt to mate with wax models, only if the wax is moved in the patterns similar to female-male courtship dances. If wax models did not carry out the dance, then ultimately the males did not attempt copulation. [32]
Although males always extend their own proboscis, this activity within the female varies greatly. Activities among three consecutive male-female courtships showed three different female behaviors: 1) no protrusion of the proboscis, 2) continued extension of the proboscis for several seconds after mounting had occurred, and 3) repeated protrusion and withdrawal of the proboscis before the male mounted. [29] The tips of the male and female probosces can be observed to be brought into contact, where they alternate with back and forth motions. [33]
D. subobscura practice nuptial feeding, a practice where a nutritional gift is transferred from one partner to another during/directly after courtship and/or copulation. In the case of D. subobscura, the gift is a regurgitated drop of liquid secreted from the male's crop, onto the female's proboscis. [34] Preventing production and exchange of nutritional gifts among D. subobscura has been shown to decrease both male mating success and egg count among females. [35]
It has been shown that males that are in good condition produce more nutritional gifts, thereby increasing their mating success. Additionally, starved females show preference for well-fed males as a way to increase the female's fecundity – this preference is speculated to be the case due to the greater quantity of drops that well-fed males produce. [36] If larger males, carrying bigger nutritional gifts, are prevented from producing their gifts, then small males are more successful in female courtship, due to better tracking of the female during the courtship dance. Larger males are seen to have slower acceleration and deceleration speeds. [37]
Reported observations of mating behavior in inbred males reveal that in most cases, active courtships were seen, but mating did not normally follow. However, prolonged dances were rare. In some instances, the male directly approaches the female, in which the female steps sideways several times in front of the stationary male, before ultimately turning away. Occasionally, the male attempts to follow the sidestep movements of the female but would often lag behind and struggle to consistently face the female. In the incident that the female stands still and extends her proboscis, the male usually would attempt to mount. More often than not, the inbred male would fall on his back, or land too far forward or too far back on the female. In the case of the latter, the female normally stands still with her wings partially extended before eventually kicking off the male. Inbred males who have continuously but unsuccessfully attempted to court a female may approach the female from the side or behind and attempt to directly mount, a behavior described as “desperation” to some scientists. These mating attempts remain unsuccessful. The observed lower mating success in inbred males has been thought to be due to lower athletic ability via physiologically-efficient muscles, sense organs, and neuromuscular coordination, rather than lower intensity of courtship. [29]
A study has displayed that the condition of D. subobscura's gut microbiota can have an effect on its mating behavior. [38] Upon suppressing the gut bacteria of female D. subobscura with antibiotics, researchers observed that these females mated faster with males that had intact microbiota. Females with intact gut bacteria were less willing to mate with males that had intact microbiota. Additionally, fecundity was seen to increase when the gut bacteria of male and female D. subobscura were suppressed through antibiotics, compared to no suppression. [38]
Analysis of D. subobscura's salivary gland has shown that its genome mimics the Drosophila karyotype, consisting of a small dot and five large acrocentric rods. Additionally, the genome does not show a chromocenter and contains high levels of chromosomal polymorphisms caused by paracentric inversions on all of the acrocentric rods. [39] Polytene drawings and photomaps helped further the study of these inversions, allowing for the finding of more than 600 different linkages and genetic markers, which encompass a majority of the euchromatic genome. [40] [41] [42] [43] More than 65 inversions have been identified. [44]
D. subobscura is frequently used in evolutionary-biological studies. [45] [46] [47] [48] [49] As D. subobscura, among others within its species group, has been reputed as a model organism for evolutionary-biological studies, its genetics and ecology have been scrutinized for more than forty years. [50] These flies have served as favorable models ever since Theodosius Dobzhansky and his colleagues published their influential works in the 1930s. [51] [52] From the species' discovery in the Palearctic realm to its colonization of North and South America, it has attracted the interests of both European and American scientists as experimental material in evolution, biology, and ecology. [53]
The D. subobscura genome has been used to track global climate change by measuring the magnitude and direction of shifts in chromosome inversion frequencies in comparison to ambient temperatures at selected European, North American. and South American sites. [54] In 21 of 22 populations of D. subobscura, genotypes seen in warm climates increased in frequency. It was shown that genetic changes in D. subobscura at these sites can be used as a possible tool to track global climate warming. [54]
Drosophila 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.
Selfish genetic elements are genetic segments that can enhance their own transmission at the expense of other genes in the genome, even if this has no positive or a net negative effect on organismal fitness. Genomes have traditionally been viewed as cohesive units, with genes acting together to improve the fitness of the organism. However, when genes have some control over their own transmission, the rules can change, and so just like all social groups, genomes are vulnerable to selfish behaviour by their parts.
Drosophila melanogaster is a species of fly in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly", "pomace fly", or "banana fly". In the wild, D. melanogaster are attracted to rotting fruit and fermenting beverages, and are often found in orchards, kitchens and pubs.
An inversion is a chromosome rearrangement in which a segment of a chromosome becomes inverted within its original position. An inversion occurs when a chromosome undergoes a two breaks within the chromosomal arm, and the segment between the two breaks inserts itself in the opposite direction in the same chromosome arm. The breakpoints of inversions often happen in regions of repetitive nucleotides, and the regions may be reused in other inversions. Chromosomal segments in inversions can be as small as 1 kilobases or as large as 100 megabases. The number of genes captured by an inversion can range from a handful of genes to hundreds of genes. Inversions can happen either through ectopic recombination between repetitive sequences, or through chromosomal breakage followed by non-homologous end joining.
The Drosophilidae are a diverse, cosmopolitan family of flies, which includes species called fruit flies, although they are more accurately referred to as vinegar or pomace flies. Another distantly related family of flies, Tephritidae, are true fruit flies because they are frugivorous, and include apple maggot flies and many pests. The best known species of the Drosophilidae is Drosophila melanogaster, within the genus Drosophila, also called the "fruit fly." Drosophila melanogaster is used extensively for studies concerning genetics, development, physiology, ecology and behaviour. Many fundamental biological mechanisms were discovered first in D. melanogaster. The fruit fly is mostly composed of post-mitotic cells, has a very short lifespan, and shows gradual aging. As in other species, temperature influences the life history of the animal. Several genes have been identified that can be manipulated to extend the lifespan of these insects. Additionally, Drosophila subobscura, also within the genus Drosophila, has been reputed as a model organism for evolutionary-biological studies, along with D. sechellia for the evolution of host specialization on the toxic noni fruit and Scaptomyza flava for the evolution of herbivory and specialist on toxic mustard leaves.
Drosophila simulans is a species of fly closely related to D. melanogaster, belonging to the same melanogaster species subgroup. Its closest relatives are D. mauritiana and D. sechellia.
The Drosophila melanogaster species subgroup contains 9 species of flies, including the best known species Drosophila melanogaster and D. simulans. The subgroup belongs to the Drosophila melanogaster species group within the subgenus Sophophora.
The mechanisms of reproductive isolation are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offspring are sterile. These barriers maintain the integrity of a species by reducing gene flow between related species.
Sexual conflict or sexual antagonism occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, particularly over the mode and frequency of mating, potentially leading to an evolutionary arms race between males and females. In one example, males may benefit from multiple matings, while multiple matings may harm or endanger females due to the anatomical differences of that species. Sexual conflict underlies the evolutionary distinction between male and female.
Drosophila pseudoobscura is a species of fruit fly, used extensively in lab studies of speciation. It is native to western North America.
A courtship display is a set of display behaviors in which an animal, usually a male, attempts to attract a mate; the mate exercises choice, so sexual selection acts on the display. These behaviors often include ritualized movement ("dances"), vocalizations, mechanical sound production, or displays of beauty, strength, or agonistic ability.
Interlocus sexual conflict is a type of sexual conflict that occurs through the interaction of a set of antagonistic alleles at two or more different loci, or the location of a gene on a chromosome, in males and females, resulting in the deviation of either or both sexes from the fitness optima for the traits. A co-evolutionary arms race is established between the sexes in which either sex evolves a set of antagonistic adaptations that is detrimental to the fitness of the other sex. The potential for reproductive success in one organism is strengthened while the fitness of the opposite sex is weakened. Interlocus sexual conflict can arise due to aspects of male–female interactions such as mating frequency, fertilization, relative parental effort, female remating behavior, and female reproductive rate.
A behaviour mutation is a genetic mutation that alters genes that control the way in which an organism behaves, causing their behavioural patterns to change.
Formally, a nuptial gift is a material presentation to a recipient by a donor during or in relation to sexual intercourse that is not simply gametes in order to improve the reproductive fitness of the donor. Often, such a gift will improve the fitness of the recipient as well. This definition implies neutral gifts, costly gifts and beneficial gifts regarding the fitness of the recipient.
Drosophila nigrospiracula is a fly species indigenous to the Sonoran Desert, spanning Arizona, Baja California, and part of Sonora, Mexico. D. nigrospiracula share the Sonoran Desert with three other species of Drosophila: D. pachea, D. mettleri, and D. mojavensis. This fly breeds on the decomposing tissues of two species of cacti that are also endemic to the region: cardón (Pachycereus pringlei) and saguaro (Carnegiea gigantea).
Laboratory experiments of speciation have been conducted for all four modes of speciation: allopatric, peripatric, parapatric, and sympatric; and various other processes involving speciation: hybridization, reinforcement, founder effects, among others. Most of the experiments have been done on flies, in particular Drosophila fruit flies. However, more recent studies have tested yeasts, fungi, and even viruses.
Seminal fluid proteins (SFPs) or accessory gland proteins (Acps) are one of the non-sperm components of semen. In many animals with internal fertilization, males transfer a complex cocktail of proteins in their semen to females during copulation. These seminal fluid proteins often have diverse, potent effects on female post-mating phenotypes. SFPs are produced by the male accessory glands.
Drosophila metlerri, commonly known as the Sonoran Desert fly, is a fly in the genus Drosophila. The species is found in North America and is most concentrated along the southern coast of California and in Mexico. D. mettleri are dependent on plant hosts, namely, the saguaro and cardon cacti. Thus, they are most prevalent in arid, desert conditions. It is able to detoxify chemicals found in the rotting liquid of cacti hosts, which allows it to use otherwise lethal soil as a nesting site.
Drosophila silvestris is a large species of fly in the family Drosophilidae that are primarily black with yellow spots. As a rare species of fruit fly endemic to Hawaii, the fly often experiences reproductive isolation. Despite barriers in nature, D. silvestris is able to breed with D. heteroneura to create hybrid flies in the laboratory.
The Hawaiian Drosophilidae are a lineage of flies within the genus Drosophila. This monophyletic clade includes all of the endemic Hawaiian Drosophila and all members of the genus Scaptomyza, which contains both Hawaiian and non-Hawaiian species. The Hawaiian Drosophilidae are descended from a common ancestor estimated to have lived 25 million years ago. Species of Hawaiian Drosophilidae flies have been studied as models of speciation and behavioral evolution. Along with other members of the native Hawaiian ecosystem, the conservations status of many species of Hawaiian Drosophilidae is threatened by habitat loss and introduced predators, among other factors.
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