HOME

TheInfoList



OR:

The term melanism refers to black pigment and is derived from the gr, μελανός. Melanism is the increased development of the dark-colored pigment
melanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...
in the skin or hair. Pseudomelanism, also called abundism, is another variant of pigmentation, identifiable by dark spots or enlarged stripes, which cover a large part of the body of the animal, making it appear melanistic. The morbid deposition of black matter, often of a malignant character causing pigmented
tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
s, is called melanosis.


Adaptation

Melanism related to the process of adaptation is called adaptive. Most commonly, dark individuals become fitter to survive and reproduce in their environment as they are better camouflaged. This makes some species less conspicuous to predators, while others, such as leopards, use it as a foraging advantage during night hunting. Typically, adaptive melanism is heritable: A dominant allele, which is entirely or nearly entirely expressed in the
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (biology), morphology or physical form and structure, its Developmental biology, developmental proc ...
, is responsible for the excessive amount of melanin. Adaptive melanism has been shown to occur in a variety of animals, including mammals such as squirrels, many cats and canids, and
coral snake Coral snakes are a large group of elapid snakes that can be divided into two distinct groups, the Old World coral snakes and New World coral snakes. There are 16 species of Old World coral snakes, in three genera (''Calliophis'', ''Hemibungarus ...
s. Adaptive melanism can lead to the creation of morphs, the most notable example being the peppered moth, whose evolutionary history in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and ...
is offered as a classic instructional tool for teaching the principles of
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Cha ...
.


Industrial melanism

Industrial melanism is an evolutionary effect in insects such as the peppered moth, '' Biston betularia'' in areas subject to industrial pollution. Darker pigmented individuals are favored by
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Cha ...
, apparently because they are better
camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
d against polluted backgrounds. When pollution was later reduced, lighter forms regained the advantage and melanism became less frequent.Grant, B. S., Wiseman L. L., 2002. Recent history of melanism in American peppered moths. Journal of Heredity 93:86-90.Grant, B. S., Cook, A. D., Clarke, C. A., & Owen, D. F. (1998). Geographic and temporal variation in the incidence of melanism in peppered moth populations in America and Britain. ''Journal of Heredity'', 89(5), 465-471. Other explanations have been proposed, such as that the melanin pigment enhances function of immune defences, or a thermal advantage from the darker coloration.Mikkola, K., Albrecht, A., 1988. The melanism of ''Adalia-bipunctata'' around the Gulf of Finland as an industrial phenomenon (Coleoptera, Coccinellidae). Annales Zoologici Fennici 25:177-85.Muggleton, J., Lonsdale, D., Benham, B. R., 1975. Melanism in ''Adalia-bipunctata L'' (ColCoccinellidae) and its relationship to atmospheric pollution. Journal of Applied Ecology 2:451-464.De Jong, P. W., Verhoog, M. D., Brakefield, P. M., 1992. Sperm competition and melanic polymorphism in the 2-spot ladybird, ''Adalla bipunctata'' (Coleoptera, Coccinellidae). Journal of Heredity 70:172-178.


In cats

Melanistic coat coloration occurs as a common polymorphism in 11 of 37 felid species and reaches high population frequency in some cases but never achieves complete fixation. The black panther, a melanistic leopard, is common in the equatorial rainforest of Malaya and the tropical rainforest on the slopes of some African mountains, such as Mount Kenya. The serval also has melanistic forms in certain areas of East Africa. In the jaguarundi, coloration varies from dark brown and gray to light reddish. Melanic forms of jaguar are common in certain parts of South America. In 1938 and 1940, two melanistic bobcats were trapped alive in sub-tropical
Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...
. In 2003, the dominant mode of inheritance of melanism in jaguars was confirmed by performing
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (biology), morphology or physical form and structure, its Developmental biology, developmental proc ...
-transmission analysis in a 116-individual captive
pedigree Pedigree may refer to: Breeding * Pedigree chart, a document to record ancestry, used by genealogists in study of human family lines, and in selective breeding of other animals ** Pedigree, a human genealogy (ancestry chart) ** Pedigree (anim ...
. Melanistic animals were found to carry at least one copy of a mutant '' MC1R'' sequence allele, bearing a 15- base pair inframe deletion. Ten unrelated melanistic jaguars were either homozygous or
heterozygous Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. ...
for this allele. A 24-base pair deletion causes the incompletely dominant allele for melanism in the jaguarundi. Sequencing of the agouti signalling peptide in the agouti gene coding region revealed a 2-base pair deletion in black domestic cats. These variants were absent in melanistic individuals of Geoffroy's cat,
oncilla The oncilla (''Leopardus tigrinus''), also known as the northern tiger cat, little spotted cat, and tigrillo, is a small spotted cat ranging from Central America to central Brazil. It is listed as Vulnerable on the IUCN Red List, and the pop ...
, pampas cat and
Asian golden cat The Asian golden cat (''Catopuma temminckii'') is a medium-sized wild cat native to the northeastern Indian subcontinent, Southeast Asia and China. It has been listed as Near Threatened on the IUCN Red List since 2008, and is threatened by poac ...
, suggesting that melanism arose independently at least four times in the cat family. Melanism in leopards is inherited as a Mendelian, monogenic recessive trait relative to the spotted form. Pairings of black animals have a significantly smaller litter size than other possible pairings. Between January 1996 and March 2009, Indochinese leopards were photographed at 16 sites in the Malay Peninsula in a sampling effort of more than 1000 trap nights. Of 445 photographs of melanistic leopards, 410 were taken south of the Kra Isthmus, where the non-melanistic morph was never photographed. These data suggest the near fixation of the dark allele in the region. The expected time to fixation of this recessive allele due to genetic drift alone ranged from about 1,100 years to about 100,000 years. Melanism in leopards has been hypothesized to be causally associated with a selective advantage for ambush. Other theories are that genes for melanism in felines may provide resistance to viral infections, or a high-altitude adaptation, since black fur absorbs more light for warmth.


In birds

The chicken breeds Silkie and
Ayam Cemani The Ayam Cemani is a rare breed of chicken from Indonesia. They have a dominant gene that causes hyperpigmentation (fibromelanosis), making the chicken mostly black, including feathers, beak, and internal organs. The Cemani is a very popula ...
commonly exhibit this trait.
Ayam Cemani The Ayam Cemani is a rare breed of chicken from Indonesia. They have a dominant gene that causes hyperpigmentation (fibromelanosis), making the chicken mostly black, including feathers, beak, and internal organs. The Cemani is a very popula ...
is an uncommon and relatively modern breed of chicken from Indonesia. They have a dominant gene that causes hyperpigmentation (Fibromelanosis), making the chicken entirely black; including feathers, beak, and internal organs. In April 2015, an extremely rare black flamingo was spotted on the Mediterranean island of Cyprus.


In amphibians

The
alpine salamander The alpine salamander (''Salamandra atra'') is a black salamander that can be found in the French Alps, and through the mountainous range in Europe. It is a member of the genus '' salamandra''. Their species name, ''atra'', may be derived from the ...
, ''Salamandra atra'', has one subspecies (''S. atra atra'') that is completely black. The pigment comes from a specific cell called a melanophore, which produce the compound melanin. There are four other subspecies of this salamander, and they have varying levels of melanin pigmentation. The subspecies have yellow spots in different concentrations or proportions. The pigment-producing cells that contribute to the yellow spots of some sub-species are called xanthophores. It appears that the fully-black phenotypes do not ever develop these xanthophores. Alpine salamanders produce a toxin from their skin, and both fully melanistic, black salamanders and spotted individuals produce the compound. Studies done that traced DNA histories have suggested that the original alpine salamander phenotype was black with some yellow spots, meaning that the fully black color evolved over time and was thus selected for over many generations.


In humans

Melanism, meaning a mutation that results in completely dark skin, does not exist in humans. Melanin is the primary determinant of the degree of skin pigmentation and protects the body from harmful ultraviolet radiation. The same ultraviolet radiation is essential for the synthesis of
vitamin D Vitamin D is a group of Lipophilicity, fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and many other biological effects. In humans, the most important compounds in this group ar ...
in skin, so lighter colored skin – less melanin – is an adaptation related to the prehistoric movement of humans away from equatorial regions, as there is less exposure to sunlight at higher latitudes. People from parts of Africa,
South Asia South Asia is the southern subregion of Asia, which is defined in both geographical and ethno-cultural terms. The region consists of the countries of Afghanistan, Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan, and Sri Lanka.;;;;; ...
, Southeast Asia, and Australia may have very dark skin, but this is not melanism.


Peutz–Jeghers syndrome

This rare genetic disorder is characterized by the development of macules with
hyperpigmentation Hyperpigmentation is the darkening of an area of skin or nails caused by increased melanin. Causes Hyperpigmentation can be caused by sun damage, inflammation, or other skin injuries, including those related to acne vulgaris.James, William; Be ...
on the lips and oral mucosa ( melanosis), as well as benign polyps in the gastrointestinal tract.


Socio-politics

The term ''melanism'' has been used on
Usenet Usenet () is a worldwide distributed discussion system available on computers. It was developed from the general-purpose Unix-to-Unix Copy (UUCP) dial-up network architecture. Tom Truscott and Jim Ellis conceived the idea in 1979, and it wa ...
,
internet forum An Internet forum, or message board, is an online discussion site where people can hold conversations in the form of posted messages. They differ from chat rooms in that messages are often longer than one line of text, and are at least tempora ...
s and blogs to mean an African-American social movement holding that dark-skinned humans are the original people from which those of other skin color originate. The term ''melanism'' has been used in this context as early as the mid-1990s and was promoted by some Afrocentrists, such as Frances Cress Welsing.


See also

* Albinism * Albino and white squirrels *
Amelanism Amelanism (also known as amelanosis) is a pigmentation abnormality characterized by the lack of pigments called melanins, commonly associated with a genetic loss of tyrosinase function. Amelanism can affect fish, amphibians, reptiles, birds, and ...
* Black squirrel * Black swan *
Erythrism Erythrism or erythrochroism refers to an unusual reddish pigmentation of an animal's hair, skin, feathers, or eggshells. Causes of erythrism include: * Genetic mutations which cause an absence of a normal pigment and/or excessive production of ot ...
* Isabellinism *
Heterochromia iridum Heterochromia is a variation in coloration. The term is most often used to describe color differences of the iris, but can also be applied to color variation of hair or skin. Heterochromia is determined by the production, delivery, and conce ...
* Leucism, a partial loss of pigmentation that results in animals with pale or white skin, hair and/or feathers * Piebaldism * Vitiligo, a skin condition which causes areas of the skin to lose its colour * Xanthochromism, an unusual yellow colouration in animals * Peutz–Jeghers syndrome * Ocular melanosis * Melanosis


References


Bibliography

* * *
Melanism and disease resistance in insects
* Fryer, G. 2013. How should the history of industrial melanism in moths be interpreted? ''The Linnean''. 29 (2): 15 - 22. {{Portal bar, Environment, Ecology, Earth sciences, Evolutionary biology Genetic disorders with no OMIM Disturbances of pigmentation Dermatologic terminology Animal coat colors