The term melanism refers to black pigment and is derived from the gr, μελανός. Melanism is the increased development of the dark-colored
pigment
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic comp ...
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 amin ...
in the
skin
Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation.
Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...
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
Heredity, also called inheritance or biological inheritance, is the passing on of traits from parents to their offspring; either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic inf ...
: A
dominant allele
An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution.
::"The chro ...
, 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 or physical form and structure, its developmental processes, its biochemical and physiological prop ...
, 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
The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...
and
canids, and
coral snakes. 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 European mainland, continental mainland. It comprises England, Scotlan ...
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
evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
ary 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
Polymorphism, polymorphic, polymorph, polymorphous, or polymorphy may refer to:
Computing
* Polymorphism (computer science), the ability in programming to present the same programming interface for differing underlying forms
* Ad hoc polymorphis ...
in 11 of 37
felid species and reaches high population frequency in some cases but never achieves complete
fixation. The
black panther
A black panther is the melanistic colour variant of the leopard (''Panthera pardus'') and the jaguar (''Panthera onca''). Black panthers of both species have excess black pigments, but their typical rosettes are also present. They have been ...
, a melanistic
leopard
The leopard (''Panthera pardus'') is one of the five extant species in the genus '' Panthera'', a member of the cat family, Felidae. It occurs in a wide range in sub-Saharan Africa, in some parts of Western and Central Asia, Southern Russia ...
, is common in the
equatorial rainforest
Tropical and subtropical moist broadleaf forests (TSMF), also known as tropical moist forest, is a subtropical and tropical forest habitat type defined by the World Wide Fund for Nature.
Description
TSMF is generally found in large, disc ...
of
Malaya
Malaya refers to a number of historical and current political entities related to what is currently Peninsular Malaysia in Southeast Asia:
Political entities
* British Malaya (1826–1957), a loose collection of the British colony of the Straits ...
and the
tropical rainforest
Tropical rainforests are rainforests that occur in areas of tropical rainforest climate in which there is no dry season – all months have an average precipitation of at least 60 mm – and may also be referred to as ''lowland equatori ...
on the slopes of some African mountains, such as
Mount Kenya. The
serval also has melanistic forms in certain areas of
East Africa
East Africa, Eastern Africa, or East of Africa, is the eastern subregion of the African continent. In the United Nations Statistics Division scheme of geographic regions, 10-11-(16*) territories make up Eastern Africa:
Due to the histori ...
. In the
jaguarundi
The jaguarundi (''Herpailurus yagouaroundi'') is a wild cat native to the Americas. Its range extends from central Argentina in the south to northern Mexico, through Central and South America east of the Andes. The jaguarundi is a medium-siz ...
, coloration varies from dark brown and gray to light reddish. Melanic forms of
jaguar
The jaguar (''Panthera onca'') is a large cat species and the only living member of the genus ''Panthera'' native to the Americas. With a body length of up to and a weight of up to , it is the largest cat species in the Americas and the thi ...
are common in certain parts of
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the souther ...
. In 1938 and 1940, two melanistic
bobcat
The bobcat (''Lynx rufus''), also known as the red lynx, is a medium-sized cat native to North America. It ranges from southern Canada through most of the contiguous United States to Oaxaca in Mexico. It is listed as Least Concern on the IU ...
s 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, a ...
.
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 or physical form and structure, its developmental processes, its biochemical and physiological prop ...
-transmission analysis in a 116-individual captive
pedigree. Melanistic animals were found to carry at least one copy of a mutant ''
MC1R
The melanocortin 1 receptor (MC1R), also known as melanocyte-stimulating hormone receptor (MSHR), melanin-activating peptide receptor, or melanotropin receptor, is a G protein–coupled receptor that binds to a class of pituitary peptide hormon ...
'' sequence
allele
An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution.
::"The chro ...
, bearing a 15-
base pair inframe deletion. Ten unrelated melanistic jaguars were either
homozygous
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.
Mo ...
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.
Mo ...
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 cat
The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...
s. 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 popula ...
,
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 poach ...
, suggesting that melanism arose independently at least four times in the cat family.
Melanism in leopards is inherited as a
Mendelian,
monogenic recessive trait
In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and ...
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
The Malay Peninsula ( Malay: ''Semenanjung Tanah Melayu'') is a peninsula in Mainland Southeast Asia. The landmass runs approximately north–south, and at its terminus, it is the southernmost point of the Asian continental mainland. The are ...
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
Genetic drift, also known as allelic drift or the Wright effect, is the change in the frequency of an existing gene variant (allele) in a population due to random chance.
Genetic drift may cause gene variants to disappear completely and there ...
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 popular g ...
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 popular g ...
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
Flamingos or flamingoes are a type of wading bird in the family Phoenicopteridae, which is the only extant family in the order Phoenicopteriformes. There are four flamingo species distributed throughout the Americas (including the Caribbean) ...
was spotted on the Mediterranean island of
Cyprus
Cyprus ; tr, Kıbrıs (), officially the Republic of Cyprus,, , lit: Republic of Cyprus is an island country located south of the Anatolian Peninsula in the eastern Mediterranean Sea. Its continental position is disputed; while it is ...
.
In amphibians
The
alpine salamander, ''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
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
. The same ultraviolet radiation is essential for the synthesis of
vitamin D
Vitamin D is a group of 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 are vitamin D3 ...
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
Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, south-eastern region of Asia, consistin ...
, and Australia may have very dark skin, but this is not melanism.
Peutz–Jeghers syndrome
This rare
genetic disorder
A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorde ...
is characterized by the development of
macules with
hyperpigmentation on the lips and
oral mucosa
The oral mucosa is the mucous membrane lining the inside of the mouth. It comprises stratified squamous epithelium, termed "oral epithelium", and an underlying connective tissue termed '' lamina propria''. The oral cavity has sometimes been des ...
(
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 was ...
,
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
blog
A blog (a truncation of "weblog") is a discussion or informational website published on the World Wide Web consisting of discrete, often informal diary-style text entries (posts). Posts are typically displayed in reverse chronological order ...
s to mean an
African-American
African Americans (also referred to as Black Americans and Afro-Americans) are an Race and ethnicity in the United States, ethnic group consisting of Americans with partial or total ancestry from sub-Saharan Africa. The term "African American ...
social movement
A social movement is a loosely organized effort by a large group of people to achieve a particular goal, typically a social or political one. This may be to carry out a social change, or to resist or undo one. It is a type of group action and m ...
holding that dark-skinned humans are the original people from which those of other
skin color
Human skin color ranges from the darkest brown to the lightest hues. Differences in skin color among individuals is caused by variation in pigmentation, which is the result of genetics (inherited from one's biological parents and or individ ...
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
Albinism is the congenital absence of melanin in an animal or plant resulting in white hair, feathers, scales and skin and pink or blue eyes. Individuals with the condition are referred to as albino.
Varied use and interpretation of the term ...
*
Albino and white squirrels
*
Amelanism
*
Black squirrel
Black squirrels are a melanistic subgroup of squirrels with black coloration on their fur. The phenomenon occurs with several species of squirrels, although it is most frequent with the eastern gray squirrel (''Sciurus carolinensis'') and the ...
*
Black swan
*
Erythrism
*
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 concentra ...
*
Leucism
Leucism () is a wide variety of conditions that result in the partial loss of pigmentation in an animal—causing white, pale, or patchy coloration of the skin, hair, feathers, scales, or cuticles, but not the eyes. It is occasionally spelled ' ...
, a partial loss of pigmentation that results in animals with pale or white skin, hair and/or feathers
*
Piebaldism
*
Vitiligo
Vitiligo is a disorder that causes the skin to lose its color. Specific causes are unknown but studies suggest a link to immune system changes.
Signs and symptoms
The only sign of vitiligo is the presence of pale patchy areas of depigmen ...
, a skin condition which causes areas of the skin to lose its colour
*
Xanthochromism, an unusual yellow colouration in animals
*
Peutz–Jeghers syndrome
Peutz–Jeghers syndrome (often abbreviated PJS) is an autosomal dominant genetic disorder characterized by the development of benign hamartomatous polyps in the gastrointestinal tract and hyperpigmented macules on the lips and oral mucosa ( ...
*
Ocular melanosis
Ocular melanosis (OM) is a blue-gray and/or brown lesion of the conjunctiva that can be separated into benign conjunctival epithelial melanosis (BCEM) and primary acquired melanosis (PAM), of which the latter is considered a risk factor for uveal ...
*
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