Domestication syndrome refers to two sets of phenotypic traits that are common to either domesticated plants [1] [2] or domesticated animals. [3]
Domesticated animals tend to be smaller and less aggressive than their wild counterparts, they may also have floppy ears, variations to coat color, a smaller brain, and a shorter muzzle. Other traits may include changes in the endocrine system and an extended breeding cycle. [3] [4] [5] These animal traits have been claimed to emerge across the different species in response to selection for tameness, which was purportedly demonstrated in a famous Russian fox breeding experiment, [6] [7] [8] though this claim has been disputed. [9] [10]
Other research [3] suggested that pleiotropic change in neural crest cell regulating genes was the common cause of shared traits seen in many domesticated animal species. However, several recent publications have either questioned this neural crest cell explanation [4] [11] [10] or cast doubt on the existence of domestication syndrome itself. [9] One recent publication [10] points out that shared selective regime changes following transition from wild to domestic environments are a more likely cause of any convergent traits. In addition, the sheer number, diversity, and phenotypic importance of neural crest cell-derived vertebrate features means that changes in genes associated with them are almost inevitable in response to any significant selective change. [10]
The process of plant domestication has produced changes in shattering/fruit abscission, shorter height, larger grain or fruit size, easier threshing, synchronous flowering, and increased yield, as well as changes in color, taste, and texture. [12]
Charles Darwin's study of The Variation of Animals and Plants Under Domestication in 1868 identified various behavioral, morphological, and physiological traits that are shared by domestic animals, but not by their wild ancestors. These shared traits became known as "the domestication syndrome", [3] a term originally used to describe common changes in domesticated grains. [1] [2] In animals, these traits include tameness, docility, floppy ears, altered tails, novel coat colors and patterns, reduced brain size, reduced body mass and smaller teeth. [3] [4] [5] Other traits include changes in craniofacial morphology, alterations to the endocrine system, and changes to the female estrous cycles including the ability to breed all year-round. [3] [5] [14]
A recent hypothesis suggests that neural crest cell behaviour may be modified by domestication, which then leads to those traits that are common across many domesticated animal species. [3] [15] [16] This hypothesis has claimed support from many gene-based studies; e.g., [17] [18] However, recent publications have disputed this support; pointing out that observed change in neural crest related genes only reveals change in neural crest-derived features. [4] [11] In effect, it is not evidence of linked trait changes in different species due to pleiotropic neural crest mechanisms as claimed by the neural crest cell hypothesis. [3] For example, all of the craniofacial skeleton is derived from the neural crest, so any animal population that experiences evolutionary change in craniofacial features will show changes in genes associated with the neural crest. The number and importance of neural crest cell features in all vertebrates means change in these features is almost inevitable under the major selective regime shifts experienced by animals making the wild to domestic transition. [10]
Many similar traits – both in animals and plants – are produced by orthologs; however, whether this is true for domestication traits or merely for wild forms is less clear. Especially in the case of plant crops, doubt has been cast because some domestication traits have been found to result from unrelated loci. [19]
In 2018, a study identified 429 genes that differed between modern dogs and modern wolves. As the differences in these genes could also be found in ancient dog fossils, these were regarded as being the result of the initial domestication and not from recent breed formation. These genes are linked to neural crest and central nervous system development. These genes affect embryogenesis and can confer tameness, smaller jaws, floppy ears, and diminished craniofacial development, which distinguish domesticated dogs from wolves and are considered to reflect domestication syndrome. The study concluded that during early dog domestication, the initial selection was for behavior. This trait is influenced by those genes which act in the neural crest, which led to the phenotypes observed in modern dogs. [18]
The 2023 parasite-mediated domestication hypothesis suggests that endoparasites such as helminths and protozoa could have mediated the domestication of mammals. Domestication involves taming, which has an endocrine component; and parasites can modify endocrine activity and microRNAs. Genes for resistance to parasites might be linked to those for the domestication syndrome; it is predicted that domestic animals are less resistant to parasites than their wild relatives. [20] [21]
A dog's cranium is 15% smaller than an equally heavy wolf's, and the dog is less aggressive and more playful. Other species pairs show similar differences. Bonobos, like chimpanzees, are a close genetic cousin to humans, but unlike the chimpanzees, bonobos are not aggressive and do not participate in lethal inter-group aggression or kill within their own group. The most distinctive features of a bonobo are its cranium, which is 15% smaller than a chimpanzee's, and its less aggressive and more playful behavior. These, and other, features led to the proposal that bonobos are a 'self-domesticated' ape. [22] [23] In other examples, the guinea pig's cranium is 13% smaller than its wild cousin the cavy, and domestic fowl show a similar reduction to their wild cousins. In a famous Russian farm fox experiment, foxes selectively bred for reduced aggression appeared to show other traits associated with domestication syndrome. This prompted the claim that domestication syndrome was caused by selection for tameness. The foxes were not selectively bred for smaller craniums and teeth, floppy ears, or skills at using human gestures, but these traits were demonstrated in the friendly foxes. Natural selection favors those that are the most successful at reproducing, not the most aggressive. Selection against aggression made possible the ability to cooperate and communicate among foxes, dogs and bonobos. [22] : 114 [24] The more docile animals have been found to have less testosterone than their more aggressive counterparts, and testosterone controls aggression and brain size. [25] The further away a dog breed is genetically from wolves, the larger the relative brain size is. [26]
The domestication syndrome was reported to have appeared in the domesticated silver fox cultivated by Dmitry Belyayev's breeding experiment. [27] However, in 2015 canine researcher Raymond Coppinger found historical evidence that Belyayev's foxes originated in fox farms on Prince Edward Island and had been bred there for fur farming since the 1800s, and that the traits demonstrated by Belyayev had occurred in the foxes prior to the breeding experiment. [28] A 2019 opinion paper by Lord and colleagues argued that the results of the "Russian farm fox experiment" were overstated, [13] although the pre-domesticated origins of these Russian foxes were already a matter of scientific record. [8]
In 2020, Wright et al. [29] argued Lord et al.'s critique refuted only a narrow and unrealistic definition of domestication syndrome because their criteria assumed it must be caused by genetic pleiotropy, and arises in response to 'selection for tameness'--as was claimed by Belyaev, [6] Trut, [7] and the proposers of the neural crest hypothesis. [3] [16] In the same year, Zeder [30] pointed out that it makes no sense to deny the existence of domestication syndrome on the basis that domestication syndrome traits were present in the pre-domesticated founding foxes.
The hypothesis that neural crest genes underlie some of the phenotypic differences between domestic and wild horses and dogs is supported by the functional enrichment of candidate genes under selection. [27] But, the observation of changed neural crest cell genes between wild and domestic populations need only reveal changes to features derived from neural crest, it does not support the claim of a common underlying genetic architecture that causes all of the domestication syndrome traits in all of the different animal species. [11]
Gleeson and Wilson [10] synthesised this debate and showed that animal domestication syndrome is not caused by selection for tameness, or by neural crest cell genetic pleiotropy. However, it could result from shared selective regime changes (which they termed 'reproductive disruption') leading to similarly shared trait changes across different species--in effect, a series of partial trait convergences. They proposed four primary selective pathways that are commonly altered by the shift to a domestic selective context, and would often lead to similar shifts in different populations. These pathways are:
Because the 'Reproductive Disruption' [10] hypothesis explains domestication syndrome as a result of changed selective regimes, it can encompass multiple genetic or physiological ways that similar traits might emerge in the different domesticated species. For example, tamer behaviour might be caused by reduced adrenal reactivity, [31] by increased oxytocin production, [32] or by a combination of these or other mechanisms, across the different populations and species.
The same concept appears in the plant domestication process which produces crops, but with its own set of syndrome traits. In cereals, these include little to no shattering [12] /fruit abscission, [19] shorter height (thus decreased lodging), larger grain [12] or fruit [19] size, easier threshing, synchronous flowering, altered timing of flowering, increased grain weight, [12] glutinousness (stickiness, not gluten protein content), [19] [12] increased fruit/grain number, altered color compounds, taste, and texture, daylength independence, determinate growth, lesser/no vernalization, less seed dormancy. [19]
Control of the syndrome traits in cereals is by:
Many of these are mutations in regulatory genes, especially transcription factors, which is likely why they work so well in domestication: They are not new, and are relatively ready to have their magnitudes altered. In annual grains, loss of function and altered expression are by far the most common, and thus are the most interesting goals of mutation breeding, while copy number variation and chromosomal rearrangements are far less common. [12]
Wheat is a grass widely cultivated for its seed, a cereal grain that is a staple food around the world. The many species of wheat together make up the genus Triticum ; the most widely grown is common wheat. The archaeological record suggests that wheat was first cultivated in the regions of the Fertile Crescent around 9600 BC. Botanically, the wheat kernel is a caryopsis, a type of fruit.
Triticale is a hybrid of wheat (Triticum) and rye (Secale) first bred in laboratories during the late 19th century in Scotland and Germany. Commercially available triticale is almost always a second-generation hybrid, i.e., a cross between two kinds of primary (first-cross) triticales. As a rule, triticale combines the yield potential and grain quality of wheat with the disease and environmental tolerance of rye. Only recently has it been developed into a commercially viable crop. Depending on the cultivar, triticale can more or less resemble either of its parents. It is grown mostly for forage or fodder, although some triticale-based foods can be purchased at health food stores and can be found in some breakfast cereals.
Domestication is a multi-generational mutualistic relationship in which an animal species, such as humans or leafcutter ants, takes over control and care of another species, such as sheep or fungi, to obtain from them a steady supply of resources, such as meat, milk, or labor. The process is gradual and geographically diffuse, based on trial and error.
Selective breeding is the process by which humans use animal breeding and plant breeding to selectively develop particular phenotypic traits (characteristics) by choosing which typically animal or plant males and females will sexually reproduce and have offspring together. Domesticated animals are known as breeds, normally bred by a professional breeder, while domesticated plants are known as varieties, cultigens, cultivars, or breeds. Two purebred animals of different breeds produce a crossbreed, and crossbred plants are called hybrids. Flowers, vegetables and fruit-trees may be bred by amateurs and commercial or non-commercial professionals: major crops are usually the provenance of the professionals.
Oryza sativa, having the common name Asian cultivated rice, is the much more common of the two rice species cultivated as a cereal, the other species being O. glaberrima, African rice. It was first domesticated in the Yangtze River basin in China 13,500 to 8,200 years ago.
The founder crops or primary domesticates are a group of flowering plants that were domesticated by early farming communities in Southwest Asia and went on to form the basis of agricultural economies across Eurasia. As originally defined by Daniel Zohary and Maria Hopf, they consisted of three cereals, four pulses, and flax. Subsequent research has indicated that many other species could be considered founder crops. These species were amongst the first domesticated plants in the world.
The domesticated silver fox is a form of the silver fox that has been to some extent domesticated under laboratory conditions. The silver fox is a melanistic form of the wild red fox. Domesticated silver foxes are the result of an experiment designed to demonstrate the power of selective breeding to transform species, as described by Charles Darwin in On the Origin of Species. The experiment at the Institute of Cytology and Genetics in Novosibirsk, Russia explored whether selection for behaviour rather than morphology may have been the process that had produced dogs from wolves, by recording the changes in foxes when in each generation only the most tame foxes were allowed to breed. Many of the descendant foxes became both tamer and more dog-like in morphology, including displaying mottled- or spotted-coloured fur.
The domestication of vertebrates is the mutual relationship between vertebrate animals including birds and mammals, and the humans who have influence on their care and reproduction.
Dmitry Konstantinovich Belyayev was a Soviet geneticist and academician who served as director of the Institute of Cytology and Genetics (IC&G) of the USSR Academy of Sciences, Novosibirsk, from 1959 to 1985. His decades-long effort to breed domesticated silver foxes was described by The New York Times as “arguably the most extraordinary breeding experiment ever conducted.” A 2010 article in Scientific American stated that Belyayev “may be the man most responsible for our understanding of the process by which wolves were domesticated into our canine companions.”
Common wheat, also known as bread wheat, is a cultivated wheat species. About 95% of wheat produced worldwide is common wheat; it is the most widely grown of all crops and the cereal with the highest monetary yield.
Triticeae is a botanical tribe within the subfamily Pooideae of grasses that includes genera with many domesticated species. Major crop genera found in this tribe include wheat, barley, and rye; crops in other genera include some for human consumption, and others used for animal feed or rangeland protection. Among the world's cultivated species, this tribe has some of the most complex genetic histories. An example is bread wheat, which contains the genomes of three species with only one being a wheat Triticum species. Seed storage proteins in the Triticeae are implicated in various food allergies and intolerances.
Marker assisted selection or marker aided selection (MAS) is an indirect selection process where a trait of interest is selected based on a marker linked to a trait of interest, rather than on the trait itself. This process has been extensively researched and proposed for plant- and animal- breeding.
Self-domestication is a scientific hypothesis that suggests that, similar to domesticated animals, there has been a process of artificial selection among members of the human species conducted by humans themselves. In this way, during the process of hominization, a preference for individuals with collaborative and social behaviors would have been shown to optimize the benefit of the entire group: docility, language, and emotional intelligence would have been enhanced during this process of artificial selection. The hypothesis is raised that this is what differentiated Homo sapiens from Homo neanderthalensis and Homo erectus.
Thinopyrum intermedium, known commonly as intermediate wheatgrass, is a sod-forming perennial grass in the Triticeae tribe of Pooideae native to Europe and Western Asia. It is part of a group of plants commonly called wheatgrasses because of the similarity of their seed heads or ears to common wheat. However, wheatgrasses generally are perennial, while wheat is an annual. It has gained the Royal Horticultural Society's Award of Garden Merit as an ornamental.
Plant genetics is the study of genes, genetic variation, and heredity specifically in plants. It is generally considered a field of biology and botany, but intersects frequently with many other life sciences and is strongly linked with the study of information systems. Plant genetics is similar in many ways to animal genetics but differs in a few key areas.
Host–parasite coevolution is a special case of coevolution, where a host and a parasite continually adapt to each other. This can create an evolutionary arms race between them. A more benign possibility is of an evolutionary trade-off between transmission and virulence in the parasite, as if it kills its host too quickly, the parasite will not be able to reproduce either. Another theory, the Red Queen hypothesis, proposes that since both host and parasite have to keep on evolving to keep up with each other, and since sexual reproduction continually creates new combinations of genes, parasitism favours sexual reproduction in the host.
Plant breeding started with sedentary agriculture, particularly the domestication of the first agricultural plants, a practice which is estimated to date back 9,000 to 11,000 years. Initially, early human farmers selected food plants with particular desirable characteristics and used these as a seed source for subsequent generations, resulting in an accumulation of characteristics over time. In time however, experiments began with deliberate hybridization, the science and understanding of which was greatly enhanced by the work of Gregor Mendel. Mendel's work ultimately led to the new science of genetics. Modern plant breeding is applied genetics, but its scientific basis is broader, covering molecular biology, cytology, systematics, physiology, pathology, entomology, chemistry, and statistics (biometrics). It has also developed its own technology. Plant breeding efforts are divided into a number of different historical landmarks.
The evolution of schizophrenia refers to the theory of natural selection working in favor of selecting traits that are characteristic of the disorder. Positive symptoms are features that are not present in healthy individuals but appear as a result of the disease process. These include visual and/or auditory hallucinations, delusions, paranoia, and major thought disorders. Negative symptoms refer to features that are normally present but are reduced or absent as a result of the disease process, including social withdrawal, apathy, anhedonia, alogia, and behavioral perseveration. Cognitive symptoms of schizophrenia involve disturbances in executive functions, working memory impairment, and inability to sustain attention.
Wild ancestors are the original species from which domesticated plants and animals are derived. Examples include dogs which are derived from wolves and flax which is derived from Linum bienne. In most cases the wild ancestor species still exists, but some domesticated species, such as camels, have no surviving wild relatives. In many cases there is considerable debate in the scientific community about the identity of the wild ancestor or ancestors, as the process of domestication involves natural selection, artificial selection, and hybridization.
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.
{{cite web}}
: Missing or empty |title=
(help)