In plant biology and agriculture, Vavilovian mimicry (also crop mimicry or weed mimicry [1] ) is a form of mimicry in plants where a weed evolves to share characteristics with a crop plant through generations of involuntary artificial selection. It is named after the Russian plant geneticist Nikolai Vavilov.
Selection against the weed may occur by killing a young or adult weed, by separating its seeds from those of the crop by winnowing, or both. The process has operated since Neolithic times, creating secondary crops such as rye and oats through mimicry of cereals such as wheat.
Vavilovian mimicry is a form of mimicry in plants where a weed of cultivation evolves to share characteristics with a crop through generations of artificial selection. [2] It is sometimes described as crop mimicry or weed mimicry. [3] It is named after Nikolai Vavilov, a prominent Russian plant geneticist of the early 20th century. [1] [4] In addition, Vavilov described as 'secondary crops' cereals such as rye that he believed derived from weeds that mimicked other cereals. [1] [2]
Evolutionary biologists describe mimicry in terms of three roles for the species involved: mimic, model, and dupe. The mimic is the species that in some ways resembles the model, creating a deception; the dupe is the species that is deceived. [2] Vavilovian mimicry is disjunct, meaning that the mimic, model, and dupe involved are all from different species. In Georges Pasteur's terms, the model is "agreeable to the dupe" (e.g. farmers intentionally plant and harvest wheat), whereas in Batesian mimicry, the model is "forbidding to the dupe" (e.g. birds find wasps unpleasant, and try to avoid them). [2]
Vavilovian mimicry can be classified as reproductive, because it provides a means for the mimic to reproduce – as when rye seeds are unintentionally sown as wheat by the farmer, or when rye seedlings or older plants are unintentionally allowed to grow in a wheat field because they look like wheat. It can further be counted as aggressive (as if parasitic), because its propagation is at the expense of the intended crop: if there is more rye in a field, there is less wheat. Finally, in the case of secondary crops, it can be considered mutualistic, as both the rye, and the farmer who grows and eats it, benefit from the process. [2]
Delbert Wiens has argued that secondary crops cannot be classified as mimics, because they result from artificial as opposed to natural selection, and because the selective agent is a machine. [5] Pasteur points out that "indirect artificial selection" is involuntary and thus no different from natural selection. Farmers do not wish to cause weeds to become steadily more difficult to separate from their crops by removing weeds which do not resemble the crops, but they have no option because the alternative is to let the weeds flourish. [2] Pasteur adds that manual selection has been occurring since the Neolithic Revolution, at which time no machinery was involved. [2]
Among the cereals, rye (Secale cereale) is derived from wild rye ( Secale montanum ), a widely distributed Mediterranean species. Rye was originally just a weed growing with wheat and barley, but came under similar selective pressures to the crops. Like wheat, it came to have larger seeds and more rigid spindles to which the seeds are attached, as farmers (intentionally or not) selected for grains that remained on the plant. Weeds such as rye were selected against by killing young or adult plants, separating its seeds from those of the crop (winnowing), or both. Further, wheat is an annual plant, while wild rye is a perennial. At the end of each growing season wheat produces seeds, while wild rye does not, and is thus destroyed when the post-harvest soil is tilled. However, occasional mutants do set seed; they were protected from destruction. Rye has thus evolved to become an annual plant, and in Vavilov's terms a secondary or mimetic crop. [1]
Rye is a hardier plant than wheat, surviving in harsher conditions. Having become preadapted as a crop through wheat mimicry, rye was then positioned to become a cultivated plant in areas where soil and climatic conditions favored its production, such as mountainous terrain. [7]
This fate is shared by oats (Avena sativa and Avena byzantina ), which also tolerate poorer conditions, and like rye, grow as a weed alongside wheat and barley. [7] Derived from a wild species ( Avena sterilis ), [8] it has thus come to be a crop in its own right. Once again paralleling wheat, rye and other cereals, oats have developed tough spindles which prevent seeds from easily dropping off, while other characteristics which help in natural dispersal have become vestigial, including the awns which allow them to self bury. [7]
Weeding of adult plants is generally impractical; instead they are separated based on properties of the seed. The gold-of-pleasure or false flax (Camelina sativa linicola) looks much like the flax plant Linum usitatissimum, and occurs alongside it in the field. This is done by a winnowing machine, which in this case acts as an inanimate dupe. Seeds that the machine throws the same distance as flax seeds have thus been selected for, making it nearly impossible to separate the seeds of these two species. [7] [9]
The flax-dodder ( Cuscuta epilinum ) is a parasitic creeper that grows around flax (linseed) plants, harming the crop. Much like the other cases, its seeds have become larger. A mutant double-seeded variety has become prevalent, as seed size has once again been the character upon which selection has acted. [7]
Selection can occur on the vegetative stage, through hand weeding. Weeding often takes place when the crop plant is very young, and at its most vulnerable. Echinochloa oryzoides , a species of grass which is found as a weed in rice (Oryza sativa) fields, looks similar to rice and its seeds are often mixed in rice and difficult to separate. This close similarity has been enhanced by the weeding process, an unintentionally selective force that increases the similarity of the weed to the crop in each subsequent generation. [9]
Agricultural science is a broad multidisciplinary field of biology that encompasses the parts of exact, natural, economic and social sciences that are used in the practice and understanding of agriculture. Professionals of the agricultural science are called agricultural scientists or agriculturists.
A cereal is a grass cultivated for its edible grain. Cereals are the world's largest crops, and are therefore staple foods. They include rice, wheat, rye, oats, barley, millet, and maize. Edible grains from other plant families, such as buckwheat and quinoa, are pseudocereals. Most cereals are annuals, producing one crop from each planting, though rice is sometimes grown as a perennial. Winter varieties are hardy enough to be planted in the autumn, becoming dormant in the winter, and harvested in spring or early summer; spring varieties are planted in spring and harvested in late summer. The term cereal is derived from the name of the Roman goddess of grain crops and fertility, Ceres.
The oat, sometimes called the common oat, is a species of cereal grain grown for its seed, which is known by the same name. Oats appear to have been domesticated as a secondary crop, as their seeds resembled those of other cereals closely enough for them to be included by early cultivators. Oats tolerate cold winters less well than cereals such as wheat, barley, and rye, but need less summer heat and more rain, making them important in areas such as Northwest Europe that have cool wet summers. They can tolerate low-nutrient and acid soils. Oats grow thickly and vigorously, allowing them to outcompete many weeds, and compared to other cereals are relatively free from diseases.
Rye is a grass grown extensively as a grain, a cover crop and a forage crop. It is grown principally in an area from Eastern and Northern Europe into Russia. It is much more tolerant of cold weather and poor soil than other cereals, making it useful in those regions; its vigorous growth suppresses weeds and provides abundant forage for animals early in the year. It is a member of the wheat tribe (Triticeae) which includes the cereals wheat and barley. Rye grain is used for bread, beer, rye whiskey, and animal fodder. In Scandinavia, rye was a staple food in the Middle Ages, and rye crispbread remains a popular food in the region. Europe produces around half of the world's rye; relatively little is traded between countries. A wheat-rye hybrid, triticale, combines the qualities of the two parent crops and is produced in large quantities worldwide. In European folklore, the Roggenwolf is a carnivorous corn demon or Feldgeist.
Trofim Denisovich Lysenko was a Soviet agronomist and scientist. He was a strong proponent of Lamarckism, and rejected Mendelian genetics in favour of his own idiosyncratic, pseudoscientific ideas later termed Lysenkoism.
Avena is a genus of Eurasian and African plants in the grass family. Collectively known as the oats, they include some species which have been cultivated for thousands of years as a food source for humans and livestock. They are widespread throughout Europe, Asia and northwest Africa. Several species have become naturalized in many parts of the world, and are regarded as invasive weeds where they compete with crop production. All oats have edible seeds, though they are small and hard to harvest in most species.
In evolutionary biology, mimicry is an evolved resemblance between an organism and another object, often an organism of another species. Mimicry may evolve between different species, or between individuals of the same species. In the simplest case, as in Batesian mimicry, a mimic resembles a model, so as to deceive a dupe, all three being of different species. A Batesian mimic, such as a hoverfly, is harmless, while its model, such as a wasp, is harmful, and is avoided by the dupe, such as an insect-eating bird. Birds hunt by sight, so the mimicry in that case is visual, but in other cases mimicry may make use of any of the senses. Most types of mimicry, including Batesian, are deceptive, as the mimics are not harmful, but Müllerian mimicry, where different harmful species resemble each other, is honest, as when species of wasps and of bees all have genuinely aposematic warning coloration. More complex types may be bipolar, involving only two species, such as when the model and the dupe are the same; this occurs for example in aggressive mimicry, where a predator in wolf-in-sheep's-clothing style resembles its prey, allowing it to hunt undetected. Mimicry is not limited to animals; in Pouyannian mimicry, an orchid flower is the mimic, resembling a female bee, its model; the dupe is the male bee of the same species, which tries to copulate with the flower, enabling it to transfer pollen, so the mimicry is again bipolar. In automimicry, another bipolar system, model and mimic are the same, as when blue lycaenid butterflies have 'tails' or eyespots on their wings that mimic their own heads, misdirecting predator dupes to strike harmlessly. Many other types of mimicry exist.
Nikolai Ivanovich Vavilov was a Russian and Soviet agronomist, botanist and geneticist who identified the centers of origin of cultivated plants. He devoted his life to the study and improvement of wheat, maize and other cereal crops that sustain the global population.
Batesian mimicry is a form of mimicry where a harmless species has evolved to imitate the warning signals of a harmful species directed at a predator of them both. It is named after the English naturalist Henry Walter Bates, who worked on butterflies in the rainforests of Brazil.
Camelina sativa is a flowering plant in the family Brassicaceae usually known as camelina, gold-of-pleasure, or false flax, but also occasionally as wild flax, linseed dodder, German sesame, or Siberian oilseed. It is native to Europe and areas of Central Asia, but cultivated as an oilseed crop mainly in Europe and in North America. It is not related to true flax, in the family Linaceae.
Avena sterilis is a species of grass weed whose seeds are edible. Many common names of this plant refer to the movement of its panicle in the wind.
Avena fatua is a species of grass in the oat genus. It is known as the common wild oat. This oat is native to Eurasia but it has been introduced to most of the other temperate regions of the world. It is naturalized in some areas and considered a noxious weed in others.
A noxious weed, harmful weed or injurious weed is a weed that has been designated by an agricultural or other governing authority as a plant that is harmful to agricultural or horticultural crops, natural habitats or ecosystems, or humans or livestock. Most noxious weeds have been introduced into an ecosystem by ignorance, mismanagement, or accident. Some noxious weeds are native, though many localities define them as necessarily being non-native. Typically they are plants that grow aggressively, multiply quickly without natural controls, and display adverse effects through contact or ingestion. Noxious weeds are a large problem in many parts of the world, greatly affecting areas of agriculture, forest management, nature reserves, parks and other open space.
Avena nuda is a species of grass with edible seeds in the oat genus Avena.
Aggressive mimicry is a form of mimicry in which predators, parasites, or parasitoids share similar signals, using a harmless model, allowing them to avoid being correctly identified by their prey or host. Zoologists have repeatedly compared this strategy to a wolf in sheep's clothing. In its broadest sense, aggressive mimicry could include various types of exploitation, as when an orchid exploits a male insect by mimicking a sexually receptive female, but will here be restricted to forms of exploitation involving feeding. For example, indigenous Australians who dress up as and imitate kangaroos when hunting would not be considered aggressive mimics, nor would a human angler, though they are undoubtedly practising self-decoration camouflage. Treated separately is molecular mimicry, which shares some similarity; for instance a virus may mimic the molecular properties of its host, allowing it access to its cells. An alternative term, Peckhamian mimicry, has been suggested, but it is seldom used.
Echinochloa oryzoides is a species of grass known by the common name early barnyard grass. Its origin is not certain but it may be Eurasia. The grass is a major weed of rice paddies; it is a serious problem as it is an effective Vavilovian mimic of rice, very difficult to separate from the crop.
A crop wild relative (CWR) is a wild plant closely related to a domesticated plant. It may be a wild ancestor of the domesticated (cultivated) plant or another closely related taxon.
A grain is a small, hard, dry fruit (caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legumes.
In evolutionary biology, mimicry in plants is where a plant evolves to resemble another organism physically or chemically. Mimicry in plants has been studied far less than mimicry in animals. It may provide protection against herbivory, or may deceptively encourage mutualists, like pollinators, to provide a service without offering a reward in return.
The agricultural weed syndrome is the set of common traits which make a plant a successful agricultural weed. Most of these traits are not, themselves, phenotypes but are instead methods of rapid adaptation. So equipped, plants of various origins - invasives, natives, mildly successful marginal weeds of agriculture, weeds of other settings - accumulate other characteristics which allow them to compete in an environment with a high degree of human management.