Melanism

The term melanism refers to black pigment and is derived from the Greek: μελανός.[2] Melanism is the increased development of the dark-colored pigment melanin in the skin or hair.

Melanistic black eastern grey squirrel
Melanistic guinea pigs are rare, and are used in rituals by Andean curanderos.[1]

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.[3]

The morbid deposition of black matter, often of a malignant character causing pigmented tumors, is called melanosis.[4]

Adaptation
A melanistic European adder (Vipera berus) compared to a normal-colored adder

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 black panthers, use it as a foraging advantage during night hunting.[5] Typically, adaptive melanism is heritable: A dominant allele, which is entirely or nearly entirely expressed in the phenotype, 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 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 is offered as a classic instructional tool for teaching the principles of natural selection.[6]

Industrial melanism
Main article: 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, apparently because they are better camouflaged against polluted backgrounds. When pollution was later reduced, lighter forms regained the advantage and melanism became less frequent.[7][8][9][10][11][12] Other explanations have been proposed, such as that the melanin pigment enhances function of immune defences,[13] or a thermal advantage from the darker coloration.[14][15][16]

In cats
See also: Black cat
Melanistic and normally coloured jaguars

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.[17] In 1938 and 1940, two melanistic bobcats were trapped alive in sub-tropical Florida.[18]

Pseudomelanism on a cheetah

In 2003, the dominant mode of inheritance of melanism in jaguars was confirmed by performing phenotype-transmission analysis in a 116-individual captive pedigree. 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 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, pampas cat and Asian golden cat, suggesting that melanism arose independently at least four times in the cat family.[19]

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.[20] 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.[21] Melanism in leopards has been hypothesized to be causally associated with a selective advantage for ambush.[22] 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 heat.[23]

In birds
White Silkie rooster
Black Silkie rooster

The Silkie chicken commonly exhibits this trait. In April 2015, an extremely rare black flamingo was spotted on the Mediterranean island of Cyprus.[24]

Ayam Cemani 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 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 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, Southeast Asia, and Australia 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 on the lips and oral mucosa (melanosis), as well as benign polyps in the gastrointestinal tract.[25]

Socio-politics
Further information: Melanin theory

The term melanism has been used on Usenet, internet forums 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[26] and was promoted by some Afrocentrists, such as Frances Cress Welsing.

gollark: That would be bad, actually.
gollark: 1/80 or so. Where are you going with this?
gollark: ?
gollark: As supreme world dictator I would A/B test things in different regions, so we could finally know things without making everyone experience a bad system.
gollark: You can blame basically all deaths ever on capitalism, or none of them.

See also

References
  1. Morales, E. (1995). The Guinea Pig : Healing, Food, and Ritual in the Andes. University of Arizona Press. ISBN 0-8165-1558-1.
  2. Liddell, H. G.; Scott, R. (1940). "μελα^νός". A Greek-English Lexicon, revised and augmented throughout by Sir Henry Stuart Jones, with the assistance of Roderick McKenzie. Oxford: Clarendon Press.
  3. Osinga, N.; Hart, P.; van VoorstVaader, P. C. (2010). "Albinistic common seals (Phoca vitulina) and melanistic grey seals (Halichoerus grypus) rehabilitated in the Netherlands". Animal Biology. 60 (3): 273−281. doi:10.1163/157075610x516493.
  4. Webster's Revised Unabridged Dictionary (1913). Melanosis Archived 2013-07-29 at the Wayback Machine. C. & G. Merriam Co. Springfield, Massachusetts. Page 910
  5. King, R.C., Stansfield, W.D., Mulligan, P.K. (2006). A Dictionary of Genetics, 7th ed., Oxford University Press
  6. Begon, M.; Townsend, C. R. & Harper, J. L. (2006). https://books.google.com/books?id=Lsf1lkYKoHEC&lpg=PR9&ots=UBO0G3ZMZn&lr=&pg=PA9&redir_esc=y#v=onepage&f=true |chapterurl= missing title (help). Ecology: From individuals to ecosystems (Fourth ed.). Malden, Oxford: Wiley Publishing. ISBN 9781405151986.
  7. Majerus, M. E. (2009). Industrial melanism in the peppered moth, Biston betularia: an excellent teaching example of Darwinian evolution in action. Evolution: Education and Outreach, 2(1), 63-74.
  8. McIntyre, N. E. (2000). Ecology of urban arthropods: a review and a call to action. Annals of the Entomological Society of America, 93(4), 825-835.
  9. Cook, L. M., Saccheri, I. J., 2013. The peppered moth and industrial melanism: evolution of a natural selection case study. Journal of Heredity 110:207-12
  10. Grant, B. S., Wiseman L. L., 2002. Recent history of melanism in American peppered moths. Journal of Heredity 93:86-90.
  11. Brakefield, P. M., Liebert, T. G., 2000. Evolutionary dynamics of declining melanism in the peppered moth in the Netherlands. Proceedings of the Royal Society of London Biology 267:1953-1957.
  12. 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.
  13. Mikkola, K., & Rantala, M. J. (2010). Immune defence, a possible nonvisual selective factor behind the industrial melanism of moths (Lepidoptera). Biological Journal of the Linnean Society, 99(4), 831-838.
  14. 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.
  15. 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.
  16. 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.
  17. Searle, A. G. (1968) Comparative Genetics of Coat Colour in Mammals. Logos Press, London
  18. Ulmer, F. A. (1941) Melanism in the Felidae, with special reference to the Genus Lynx. Journal of Mammalogy 22 (3): 285–288.
  19. Eizirik, E.; Yuhki, N.; Johnson, W. E.; Menotti-Raymond, M.; Hannah, S. S.; O'Brien, S. J. (2003). "Molecular Genetics and Evolution of Melanism in the Cat Family". Current Biology. 13 (5): 448–453. doi:10.1016/S0960-9822(03)00128-3. PMID 12620197.
  20. Robinson, R. (1970). "Inheritance of black form of the leopard Panthera pardus". Genetica. 41 (1): 190–197. doi:10.1007/BF00958904. PMID 5480762.
  21. Kawanishi, K.; Sunquist, M. E.; Eizirik, E.; Lynam, A. J.; Ngoprasert, D.; Wan Shahruddin, W. N.; Rayan, D. M.; Sharma, D. S. K.; Steinmetz, R. (2010). "Near fixation of melanism in leopards of the Malay Peninsula". Journal of Zoology. 282 (3): 201–206. doi:10.1111/j.1469-7998.2010.00731.x.
  22. Majerus, M. E. N. (1998). Melanism: evolution in action. Oxford University Press, New York
  23. Seidensticker, J., Lumpkin, S. (2006). Smithsonian Q & A: the ultimate question and answer book. Cats. Collins, New York
  24. Krol, Charlotte (2015-04-09). "Rare black flamingo spotted in Cyprus". The Telegraph. Archived from the original on 2015-04-25. Retrieved 2015-05-16.
  25. Broomfield, Denis. "Would Journal Clinic Case". Would Journal Clinic Case.
  26. "Sundiata, AFROCENTRISM: THE ARGUMENT WE'RE REALLY HAVING". Retrieved 2007-06-23.

Bibliography
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