Dwarfing is a process in which a

breed A breed is a specific group of domestic animals having homogeneous appearance (phenotype), homogeneous behavior, and/or other characteristics that distinguish it from other organisms of the same species. In literature, there exist several slig ...

of animals or

cultivar A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture ...

of plants is changed to become significantly smaller than standard members of their species. The effect can be induced through human intervention or non-human processes, and can include genetic, nutritional or hormonal means. Used most specifically, dwarfing includes pathogenic changes in the structure of an organism (for example, the bulldog, a genetically

achondroplastic Achondroplasia is a genetic disorder with an autosomal dominant pattern of inheritance whose primary feature is dwarfism. In those with the condition, the arms and legs are short, while the torso is typically of normal length. Those affected ...

dog breed), in contrast to non-pathogenic proportional reduction in stature (such as the whippet, a small sighthound dog breed).

Animals

In animals, including humans, dwarfism has been described in several ways. Shortened stature can result from

growth hormone deficiency Growth hormone deficiency (GHD), or human growth hormone deficiency, is a medical condition resulting from not enough growth hormone (GH). Generally the most noticeable symptom is that an individual attains a short height. Newborns may also prese ...

starvation Starvation is a severe deficiency in caloric energy intake, below the level needed to maintain an organism's life. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, de ...

, portal systemic shunts, renal disease,

hypothyroidism Hypothyroidism (also called ''underactive thyroid'', ''low thyroid'' or ''hypothyreosis'') is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone. It can cause a number of symptoms, such as ...

diabetes mellitus Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...

and other conditions. Any of these conditions can be established in a population through

genetic engineering Genetic engineering, also called genetic modification or genetic manipulation, is the modification and manipulation of an organism's genes using technology. It is a set of technologies used to change the genetic makeup of cells, including ...

selective breeding Selective breeding (also called artificial selection) 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 ...

, or

insular dwarfism Insular dwarfism, a form of phyletic dwarfism, is the process and condition of large animals evolving or having a reduced body size when their population's range is limited to a small environment, primarily islands. This natural process is disti ...

, or some combination of the above. Dwarfing can produce more practical breeds that can fit in small accommodations, or may appeal aesthetically, as well as other associated side effects. Smaller stature may be a deliberate goal of breeding programs, or it may be a side effect of other breeding goals.

Nonpurposeful dwarfing

In some husbandry conditions, humans created dwarf breeds, or allowed them to develop, without specifically selecting for smaller animals. It is likely that the Shetland sheep breed, Shetland collie breed of dogs, and various pony breeds of horses developed in this manner. In the case of the Shetland sheep and collies, it is likely that environmental conditions, such as a lack of abundant fodder, led to farmers selecting smaller animals who continued to reproduce on limited food over larger animals who did not reproduce well on limited diets. In this case, the emphasis was on selecting for survival and reproduction, not size.

Purposeful dwarfing

Humans have encouraged the deliberate development of dwarf breeds of many domestic animals, including horses, cattle, dogs, and chickens. Some have been breeds of smaller animals that were not originally selected for size, but are now held to specific sizes by a breed standard. In many cases, the exact physiological mechanism that alters the growth of individuals in that breed is not well known, and some breeds have multiple mechanisms at play. As the genetic mutations that cause dwarfing occur in many species, dwarf animals can be the offspring of normal-appearing animals. Even in breeds which have not been selected for dwarfing, some genetic lines may show a tendency to produce dwarfs, which may be encouraged by deliberate breeding. This often takes the form of in-breeding to concentrate recessive genes, and can result in other genetic abnormalities being established in the population. Some animal breeds that have been formally subject to dwarfing include: * Rabbits (

American Fuzzy Lop The American Fuzzy Lop is a rabbit breed recognized by the American Rabbit Breeders Association (ARBA). It is similar in appearance to a Holland Lop. However, the American Fuzzy Lop is a wool breed and will have wool similar to the Angora rabbit, A ...

, Britannia Petite (US), Dwarf Hotot, Florida White Rabbit, Jersey Wooly, Lionhead Polish (UK), Holland Lop Netherland Dwarf, Mini Rex, Mini Satin, others) * Dogs (

English Bulldog The Bulldog is a British breed of dog of mastiff type. It may also be known as the English Bulldog or British Bulldog. It is of medium size, a muscular, hefty dog with a wrinkled face and a distinctive pushed-in nose.French Bulldog,

Chihuahua Chihuahua may refer to: Places * Chihuahua (state), a Mexican state **Chihuahua (dog), a breed of dog named after the state **Chihuahua cheese, a type of cheese originating in the state **Chihuahua City, the capital city of the state **Chihuahua Mu ...

, Corgi, Whippet, Miniature Pinscher, others) * Poultry (Bantum chickens, Call Ducks) * Goats ( Nigerian Dwarf, Pygmy Goat) * Cattle (Dwarf Brahman, Lowline cattle Guinea Cracker Cattle, Dexter cattle) * Equines (Miniature Donkey, Fell Pony,

Hackney Pony The Hackney pony is a breed of pony closely related to the Hackney horse. Originally bred to pull carriages, they are used today primarily as show ponies. The breed does not have its own stud book, but shares one with the Hackney horse in ...

Miniature horse, Shetland Pony, others)

Plants

As with animals, plants can be dwarfed through

and

, but can also undergo natural, morphological changes to acclimatize to environmental stresses such as soil quality,Hutchings, M. J.; de Kroon, H. (1994), "Foraging in Plants: The Role of Morphological Plasticity in Resource Acquisition", ''Adv. Ecol. Res.'' 25: 159–238 light, drought, flood,Else, M. A.; et al. (1996), "Stomatal Closure in Flooded Tomato Plants Involves Abscisic Acid and a Chemically Unidentified Anti-Transpirant in Xylem Sap", ''Plant Physiol'' 112: 239-247 cold,Okamoto, T.; Tsurumi, S.; Shibasaki, K.; Obana, Y.; Takaji, H.; Oono Y.; Rahman, A. (2008), "Genetic Dissection of Hormonal Responses in the Roots of ''Arabidopsis'' Grown Under Continuous Mechanical Impedance", ''Plant Physiol.'' 146: 1651–1662 infection,Scholthof, H. B.; Scholthof, K. B. G.; Jackson, A. O. (1995), "Identification of Tomato Bushy Stunt Virus Host-Specific Symptom Determinants by Expression of Individual Genes from a Potato Virus X Vector", ''Plant Cell'' 7: 1157-1172 and

herbivory A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

Chouinard, A.; Filion, L. (2005), "Impact of Introduced White-Tailed Deer and Native Insect Defoliators on the Density and Growth of Conifer Saplings on Anticosti Island, Quebec", ''Ecoscience'' 12: 506-518 resulting in a dwarfed stature. Plants dwarfed due to environmental stress are said to be " stunted." The majority of dwarfing in plants occurs not from the damage environmental stresses inflict on them, but instead by hormones produced in response to the stress.Zhang, Y.; Turner, J. G. (2008), "Wound-Induced Endogenous Jasmonates Stunt Plant Growth by Inhibiting Mitosis", ''PLoS ONE'' 3: e3699

Plant hormone Plant hormone (or phytohormones) are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, from embryogenesis, the regulation of organ size, pat ...

s act as a signal to the various tissues of plants inducing one or more responses, the class of

plant hormone Plant hormone (or phytohormones) are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, from embryogenesis, the regulation of organ size, pat ...

responsible for dwarfing in plants due to injury are called

jasmonate Jasmonate (JA) and its derivatives are lipid-based plant hormones that regulate a wide range of processes in plants, ranging from growth and photosynthesis to reproductive development. In particular, JAs are critical for plant defense against her ...

s. Such responses include, but are not limited to: less frequent cell divisions and reduction of cell elongation.Swarup, R.; Perry, P.; Hagenbeek, D.; Van Der Straeten, D.; Beemster, G. T. S.; et al. (2007), "Ethylene Upregulates Auxin Biosynthesis in ''Arabidopsis'' Seedlings to Enhance Inhibition of Root Cell Elongation", ''Plant Cell'' 19: 2186–2196

Dwarfing trees

horticulture Horticulture is the branch of agriculture that deals with the art, science, technology, and business of plant cultivation. It includes the cultivation of fruits, vegetables, nuts, seeds, herbs, sprouts, mushrooms, algae, flowers, seaweeds and no ...

, dwarfing can be considered a desirable characteristic in modern

orchard An orchard is an intentional plantation of trees or shrubs that is maintained for food production. Orchards comprise fruit- or nut-producing trees which are generally grown for commercial production. Orchards are also sometimes a feature of ...

s. This kind of dwarfing can be attained through

, or more often, scions are grafted on to dwarfing rootstocks. Almost all modern

apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus '' Malus''. The tree originated in Central Asia, where its wild ancest ...

s in commercial use are propagated as dwarf or semi-dwarf trees for ease of picking and spraying. Dwarfing fruit trees acts through a reduction in the nutrients which travel from the roots through the trunk to the leaves and buds. Many commercial orchards of various species use this technique to improve the overall health and productivity of the individual trees. An individual tree may be made up of three or more separate cultivars - one for the root system, which is generally selected for good stability and resistance to soil-borne diseases, one for the trunk, which modifies the overall height of the tree, and one for the productive limbs and buds, which actually produces the fruit. Frequently, the root system stock is the most resistant to cold damage - both by natural selection and by protection from the cold air by the earth. When frost severely damages a tree, the more productive branch and bud cultivar may be killed off, leaving the root to sprout new stalks. In the case of oranges and other citrus, this results in sweet orange trees being frozen back so that the more hardy, cold-tolerant sour orange rootstock puts out new growth.

Dwarfing grains

Dwarfing genes are widely used in creating more productive food plants, such as grains. One condition that results in loss of grain crops is called 'lodging', where heavy ears of almost ripe grain bend the stalk until the grain touches the ground, becomes wet, and spoils. During the

Green Revolution The Green Revolution, also known as the Third Agricultural Revolution, was a period of technology transfer initiatives that saw greatly increased crop yields and agricultural production. These changes in agriculture began in developed countrie ...

, research that identified wheat reduced-height genes (''Rht'') and a rice semidwarf gene (''sd1'') resulted in crops that yielded significantly more harvestable grain.

References

{{reflist, 2 Horticulture Livestock Organism size