Thelytoky (from the Greek thēlys "female" and tokos "birth") is a type of parthenogenesis in which females are produced from unfertilized eggs, as for example in aphids. Thelytokous parthenogenesis is rare among animals and reported in about 1,500 species, about 1 in 1000 of described animal species, according to a 1984 study. It is more common in invertebrates, like arthropods, but it can occur in vertebrates, including salamanders, fish, and reptiles such as some whiptail lizards.
Thelytoky can occur by different mechanisms, each of which has a different impact on the level of homozygosity. It is found in several groups of Hymenoptera, including Apidae, Aphelinidae, Cynipidae, Formicidae, Ichneumonidae, and Tenthredinidae. It can be induced in Hymenoptera by the bacteria Wolbachia and Cardinium.
Hymenoptera (ants, bees, wasps, and sawflies) have a haplodiploid sex-determination system. They produce haploid males from unfertilized eggs (arrhenotoky), a form of parthenogenesis. However, in a few social hymenopterans, queens or workers are capable of producing diploid female offspring by thelytoky. The daughters produced may or may not be complete clones of their mother depending on the type of parthenogenesis that takes place. The offspring can develop into either queens or workers. Examples of such species include the Cape bee, Apis mellifera capensis, Mycocepurus smithii and clonal raider ant, Cerapachys biroi.
Automixis is a form of thelytoky. In automictic parthenogenesis, meiosis takes place and diploidy is restored by fusion of first division non-sister nuclei (central fusion) or the second division sister nuclei (terminal fusion). (see diagram).
Automixis with central fusion tends to maintain heterozygosity in the passage of the genome from mother to daughter. This form of automixis has been observed in several ant species including the desert ant Cataglyphis cursor, the clonal raider ant Cerapachys biroi, the predaceous ant Platythyrea punctata, and the electric ant (little fire ant) Wasmannia auropunctata. Automixis with central fusion also occurs in the Cape honey bee Apis mellifera capensis, the brine shrimp Artemia parthenogenetica, and the termite Embiratermes neotenicus.
Oocytes that undergo automixis with central fusion often display a reduced rate of crossover recombination. A low rate of recombination in automictic oocytes favors maintenance of heterozygosity, and only a slow transition from heterozygosity to homozygosity over successive generations. This allows avoidance of immediate inbreeding depression. Species that display central fusion with reduced recombination include the ants P. punctata and W. auropunctata, the brine shrimp A. parthenogenetica, and the honey bee A. m. capensis. In A. m. capensis, the recombination rate during the meiosis associated with thelytokus parthenogenesis is reduced by more than 10-fold. In W. auropunctata the reduction is 45-fold.
Single queen colonies of the narrow headed ant Formica exsecta provide an illustrative example of the possible deleterious effects of increased homozygosity. In this ant the level of queen homozygosity is negatively associated with colony age. Reduced colony survival appears to be due to decreased queen lifespan resulting from queen homozygosity and expression of deleterious recessive mutations (inbreeding depression).
Automixis with terminal fusion tends to promote homozygosity in the passage of the genome from mother to daughter. This form of automixis has been observed in the water flea Daphnia magna and the Colombian rainbow boa constrictor Epicrates maurus. Parthenogenesis in E. maurus is only the third genetically confirmed case of consecutive virgin births of viable offspring from a single female within any vertebrate lineage. However, survival of offspring over two successive litters was poor, suggesting that automixis with terminal fusion leads to homozygosity and expression of deleterious recessive alleles (inbreeding depression).
Arrhenotoky (from Greek -τόκος -tókos "birth of -" + ἄρρην árrhēn "male person"), also known as arrhenotokous parthenogenesis, is a form of parthenogenesis in which unfertilized eggs develop into males. In most cases, parthenogenesis produces exclusively female offspring, hence the distinction.
The set of processes included under the term arrhenotoky depends on the author: arrhenotoky may be restricted to the production of males that are haploid (haplodiploidy); may include diploid males that permanently inactivate one set of chromosomes (parahaploidy); or may be used to cover all cases of males being produced by parthenogenesis (including such cases as aphids, where the males are XO diploids). The form of parthenogenesis in which females develop from unfertilized eggs is known as thelytoky; when both males and females develop from unfertilized eggs, the term "deuterotoky" is used.In the most commonly used sense of the term, arrhenotoky is synonymous with haploid arrhenotoky or haplodiploidy: the production of haploid males from unfertilized eggs in insects having a haplodiploid sex-determination system. Males are produced parthenogenetically, while diploid females are usually produced biparentally from fertilized eggs. In a similar phenomenon, parthenogenetic diploid eggs develop into males by converting one set of their chromosomes to heterochromatin, thereby inactivating those chromosomes. This is referred to as diploid arrhenotoky or parahaploidy.Arrhenotoky occurs in members of the insect order Hymenoptera (bees, ants, and wasps) and the Thysanoptera (thrips). The system also occurs sporadically in some spider mites, Hemiptera, Coleoptera (bark beetles), and rotifers.Brevipalpus
Brevipalpus is a genus of mites in the family Tenuipalpidae, the flat mites. The genus includes several species that are among the most important economic pests in the flat mite family.Some Brevipalpus species are made up mostly of female individuals that reproduce via thelytoky, producing offspring without fertilization. Male individuals occur but often become feminized by Cardinium bacteria that colonize their bodies.Between each developmental stage, the juvenile rests as a chrysalis on a plant.
Brevipalpus mites damage their host plants by inserting their relatively long mouthparts into the plant tissue and injecting saliva during feeding. The saliva is toxic to the plant. Damage on grapefruit, for example, takes the form of circular, discolored lesions on the fruit which darken as they become necrotic. On pistachio, Brevipalpus damage appears as scabby blotches on the leaf petioles, stems, and nuts. Furthermore, several of these mites are vectors for a variety of serious plant viruses.Familiar species include:
Brevipalpus californicus, a mite known as a vector for the orchid fleck virus, which causes spots and rings on orchid leaves. The mite has a wide range of host plants. It has been known to form galls on bitter orange.
Brevipalpus chilensis, which is native to Chile, but has the potential to invade other regions as an agricultural pest of several crops, including grapes and citrus.
Brevipalpus lewisi, which is known from the Palearctic region, Australia, and the southwestern United States. It is a pest on pistachio, citrus, pomegranate, walnuts, grapes, and ornamental plants.
Brevipalpus obovatus, which is a pest of many plants, including the ornamentals Hibiscus rosa-sinensis and Brunfelsia uniflora.
Brevipalpus phoenicis, a pest of the tea plant, especially in Indonesia. It feeds on the leaves and in large numbers can reduce yields. It has also been observed on tangerine. This mite is a vector for Cilevirus, a plant virus that causes the disease citrus leprosis. Manifestations of the disease on a citrus tree include chlorotic lesions, girdling, fruit drop, defoliation, and the death of the tree. Of the major types of citrus, the orange is most vulnerable to the virus. The mite is also a vector of passion fruit green spot virus and coffee ringspot virus, and ringspots of Cestrum and Solanum plants.Brine shrimp
Artemia is a genus of aquatic crustaceans also known as brine shrimp. Artemia, the only genus in the family Artemiidae, has changed little externally since the Triassic period. The first historical record of the existence of Artemia dates back to the first half of the 10th century AD from Urmia Lake, Iran, with an example called by an Iranian geographer an "aquatic dog", although the first unambiguous record is the report and drawings made by Schlösser in 1757 of animals from Lymington, England. Artemia populations are found worldwide in inland saltwater lakes, but not in oceans. Artemia are able to avoid cohabiting with most types of predators, such as fish, by their ability to live in waters of very high salinity (up to 25%).The ability of the Artemia to produce dormant eggs, known as cysts, has led to extensive use of Artemia in aquaculture. The cysts may be stored for long periods and hatched on demand to provide a convenient form of live feed for larval fish and crustaceans. Nauplii of the brine shrimp Artemia constitute the most widely used food item, and over 2000 tonnes of dry Artemia cysts are marketed worldwide annually. In addition, the resilience of Artemia makes them ideal animals for running biological toxicity assays and it has become a model organism used to test the toxicity of chemicals. Breeds of Artemia are sold as novelty gifts under the marketing name Sea-Monkeys or Aqua Dragons.Cape honey bee
The Cape honey bee or Cape bee (Apis mellifera capensis) is a southern South African subspecies of the Western honey bee. They play a major role in South African agriculture and the economy of the Western Cape by pollinating crops and producing honey in the Western Cape region of South Africa.
The Cape honey bee is unique among honey bee subspecies because workers can lay diploid, female eggs, by means of thelytoky, while workers of other subspecies (and, in fact, unmated females of virtually all other eusocial insects) can only lay haploid, male eggs. Not all workers are capable of thelytoky - only those expressing the thelytoky phenotype, which is controlled by a recessive allele at a single locus (workers must be homozygous at this locus to be able to reproduce by thelytoky).Cataglyphis cursor
Cataglyphis cursor is a species of ant in the genus Cataglyphis. Described in 1846, it is known only from the Mediterranean parts of France.Drosophila mercatorum
Drosophila mercatorum is a species of fruit fly in the genus Drosophila, repleta subgroup, described by Patterson and Wheeler in 1942. Thought to be native to South America, its subspecies D. m. mercatorum now has a cosmopolitan distribution. The other subspecies, D. m. pararepleta, is confined to the east of the Andes mountains.
It is used in scientific studies of parthenogenesis since it was discovered to have low levels of naturally occurring thelytoky.Electric ant
The electric ant (Wasmannia auropunctata), also known as the little fire ant, is a small (approx 1.5 mm long), light to golden brown (ginger) social ant native to Central and South America, now spread to parts of Africa (including Gabon and Cameroon), North America, Puerto Rico, Israel, Cuba, and six Pacific Island groups (including the Galápagos Islands, Hawaii, New Caledonia and the Solomon Islands) plus north-eastern Australia (Cairns).The name, electric ant (or little fire ant) derives from the ant's painful sting relative to its size. This ant's impact in those environments and countries outside of its place of origin has been described as follows:
Wasmannia auropunctata .. is blamed for reducing species diversity, reducing overall abundance of flying and tree-dwelling insects, and eliminating arachnid populations. It is also known for its painful stings. On the Galápagos, it eats the hatchlings of tortoises and attacks the eyes and cloacae of the adult tortoises. It is considered to be perhaps the greatest ant species threat in the Pacific region.Encarsia formosa
Encarsia formosa is a species of chalcidoid wasp and a well known parasitoid of greenhouse whitefly, one of the first to be used commercially for biological pest control, from the 1920s. They can use at least 15 species of whitefly as a host, including Bemisia tabaci and Aleyrodes proletella.The tiny females (about 0.6 mm long) are black with a yellow abdomen and opalescent wings. This species reproduces asexually via thelytoky induced by Wolbachia infection. Males are produced only rarely. They are slightly larger than females and are completely black in coloration.Hymenoptera
Hymenoptera is a large order of insects, comprising the sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones.Females typically have a special ovipositor for inserting eggs into hosts or places that are otherwise inaccessible. The ovipositor is often modified into a stinger. The young develop through holometabolism (complete metamorphosis)—that is, they have a worm-like larval stage and an inactive pupal stage before they mature.Inbreeding avoidance
Inbreeding avoidance, or the inbreeding avoidance hypothesis, is a concept in evolutionary biology that refers to the prevention of the deleterious effects of inbreeding. The inbreeding avoidance hypothesis posits that certain mechanisms develop within a species, or within a given population of a species, as a result of natural and sexual selection in order to prevent breeding among related individuals in that species or population. Although inbreeding may impose certain evolutionary costs, inbreeding avoidance, which limits the number of potential mates for a given individual, can inflict opportunity costs. Therefore, a balance exists between inbreeding and inbreeding avoidance. This balance determines whether inbreeding mechanisms develop and the specific nature of said mechanisms.Inbreeding results in inbreeding depression, which is the reduction of fitness of a given population due to inbreeding. Inbreeding depression occurs via one of two mechanisms. The first mechanism involves the appearance of disadvantageous traits via the pairing of deleterious recessive alleles in a mating pair’s progeny. When two related individuals mate, the probability of deleterious recessive alleles pairing in the resulting offspring is higher as compared to when non-related individuals mate. The second mechanism relates to the increased fitness of heterozygotes.
A review of the genetics of inbreeding depression in wild animal and plant populations, as well as in humans, led to the conclusion that inbreeding depression and its opposite, heterosis (hybrid vigor), are predominantly caused by the presence of recessive deleterious alleles in populations. Inbreeding, including self-fertilization in plants and automictic parthenogenesis (thelytoky) in hymenoptera, tends to lead to the harmful expression of deleterious recessive alleles (inbreeding depression). Cross-fertilization between unrelated individuals ordinarily leads to the masking of deleterious recessive alleles in progeny.Many studies have demonstrated that homozygous individuals are often disadvantaged with respect to heterozygous individuals. For example, a study conducted on a population of South African cheetahs demonstrated that the lack of genetic variability among individuals in the population has resulted in negative consequences for individuals, such as a greater rate of juvenile mortality and spermatozoal abnormalities. When heterozygotes possess a fitness advantage relative to a homozygote, a population with a large number of homozygotes will have a relatively reduced fitness, thus leading to inbreeding depression. Through these described mechanisms, the effects of inbreeding depression are often severe enough to cause the evolution of inbreeding avoidance mechanisms.Laying worker bee
A laying worker bee is a worker bee that lays unfertilized eggs usually in the absence of a queen bee (cf gamergates in ants). Only drones develop from the eggs of laying worker bees (with some exceptions, see thelytoky). A beehive cannot survive with only a laying worker bee.Lorryia formosa
Lorryia formosa, commonly known as the yellow mite or the citrus yellow mite, is a species of acariform mite. They are in the subfamily Tydeinae of the family Tydeidae. Commonly found on the foliage of citrus trees around the world, Lorryia formosa also associates with a variety of other plant types. The life cycle includes six discrete stages of development, and the lifespan averages about 37 days. The females of the species use an asexual form of reproduction where the growth and development of embryos occurs without fertilization by a male, a process called thelytoky.Muscidifurax uniraptor
Muscidifurax uniraptor is a species of wasp (the taxonomic order Hymenoptera) in the family Pteromalidae. The species does not currently have a common name. M. uniraptor is a pupal parasitoid of synanthropic filth-breeding Diptera and is a natural enemy of the housefly Musca domestica and the stable fly Stomoxys calcitrans.Ooceraea biroi
Ooceraea biroi, the clonal raider ant, is a queenless clonal ant in the genus Ooceraea (recently transferred from the genus Cerapachys). Native to the Asian mainland, this species has become invasive on tropical and subtropical islands throughout the world. Unlike most ants, which have reproductive queens and mostly nonreproductive workers, all individuals in a O. biroi colony reproduce clonally via thelytokous parthenogenesis. Like most dorylines, O. biroi are obligate myrmecophages and raid nests of other ant species to feed on the brood.Platythyrea
Platythyrea is a genus of predaceous ants in the subfamily Ponerinae and the sole member of the tribe Platythyreini.Queen bee
The term "queen bee" is typically used to refer to an adult, mated female (gyne) that lives in a honey bee colony or hive; she is usually the mother of most, if not all, of the bees in the beehive. Queens developed from larvae selected by worker bees and specially fed in order to become sexually mature. There is normally only one adult, mated queen in a hive, in which case the bees will usually follow and fiercely protect her.
The term "queen bee" can be more generally applied to any dominant reproductive female in a colony of a eusocial bee species other than honey bees. However, as in the Brazilian stingless bee Schwarziana quadripunctata, a single nest may have multiple queens or even dwarf queens, ready to replace a dominant queen in a case of sudden death.Taeniogonalos
Taeniogonalos is a genus of wasps in the family Trigonalidae.Tetrastichinae
Tetraschininae is a subfamily of the chalcid wasp family Eulophidae. It is one of the largest subfamilies of the Eulophidae containing over 100 genera and nearly 3,000 species. The species of the family Tetrastichinae are found in almost any type of terrestrial habitat and have a worldwide distribution, except Antarctica. They show a varied biology and hosts for Tetraschine wasps have been identified from over 100 different insect families, across 10 different orders and they have also been recorded as being parasitoids on nematodes, mites and spiders' eggs. Some species are even phytophagous, while others are inquilines and yet others are gall formers.Trichadenotecnum
Trichadenotecnum is a genus of insects in the order Psocoptera, the booklice, barklice, and bookflies. It is one of the largest genera, including over 200 described species.The biology of the genus is similar to that of many other booklice. T. alexanderae, for example, feeds on pleurococcine algae and the female reproduces by mating with a male. In some closely related species, the females instead undergo thelytoky, producing eggs without fertilization.Trichadenotecnum is well separated from related genera, forming a monophyletic group. The large genus is divided into several clades, some of which are further divided into subclades. These groups are mainly separated on the basis of the morphology of the genitalia, which is quite variable in this genus. The male genitalia are the most important structures used to distinguish species. Some males have distinctly asymmetrical genitalia.In general, these insects have forewings that are about 2 or 3 millimeters long and have variable spotted patterns.Trichadenotecnum occur throughout most of the world, except for Australia and New Zealand, which have no native species.