Melanism in Animals
Several species of animal come in a black color 'morph' as well as their regular color. This dark coloring is usual cased by genetically-determined melanism (also called melanosis). basically this term refers to any increase in dark pigment which may cause brown coloring or black patches or markings--but in the most extreme cases results in black or near black over most or all of the body.
There is considerable debate as to whether rates of melanism in populations of animals reflects adaptive evolution, such that if the environment becomes darker more animals in the population will be melanistic. One specific example being that soot produced by factories led to an increased in the number of black-colored peppered moths (see: peppered moth, pocket mouse).
Melanism is thought to occur more often at high altitudes, particularly in insects. In some cases it is also thought to be linked to improved disease resistance. Black morphs seem to be more common in areas with viral infections and it may be because they possess a stronger immune response and so are more likely to survive and breed.
Melanism is typically a dominant gene. So even when it is neutral in its effects it will tend to persist in an animal population over time.
Black animals often have a sinister meaning in myth and superstition. In Britain black rabbits were though to carry human souls, and a black cat might be a witch in animal form or her familiar. Other beliefs more idiosyncratic, for example if a black moth flies into your face it is meant to mean that someone has written you a letter.
Red foxes sometime appear in a black color morph called the "silver fox" or sometimes the "cross fox". This example was seen in Colorado in 2009. And another in Newfoundland (2008) more clearly showing the typical white tail tip and white "guard" hairs over the black coat which can produce a silver-gray effect.
Domestically bred lines of silver fox are raised commerically in cages for their fur, and a domesticated line has been developed in Russia to be kept as pets.
For other examples see: Austraiia (2007).
You will sometimes see coyotes referred to as "black phase" or "swamp coyotes". These are just local terms for coyotes with a black coat. They are quite rare and some people insist they are crosses with dogs rather than true coyotes. (Examples: South Carolina 2009)
Both grey and red wolves sometimes occur in melanistic forms. Research suggests that these have occurred through hybridization with dogs. The black-coat genes seems to have spread widely in wolves that live in wooded areas, where it may help them blend in to the background. So this may be a rare case where imported genetics proved to be beneficial to the wild species.
Most species of deer occasionally display melanism. Pictures by Richard Buquoi (example right) clearly show that melanism is a color morph that occurs spontaneously (veracity of these pictures is confirmed by Snopes). The whitetail doe and the melanistic fawn's twin display normal coloration for the species.
Melanism has also been seen in deer in Texas.
A black morph many people may have seen is the Eastern Gray Squirrel.
Melanism is recessive in these squirrels so depending on the parents you will see black and gray offspring from the same nest. Examples in this thread.
Melanism can also be partial. For example this squirrel has a black body but a red tail.
Melanism is found in a wide variety of fish species. It is particularly striking in this clownfish, seen here next to a normally colored companion.
Mosquito Fish (Gambusia holbrooki)
Another species that shows partial melanism, just the males may show dalmation spots. These melanic males are not just different in appearance, but also behavior--for example they are more aggressive in their pursuit of females.
There are historical examples of black tigers, but currently most are pseudo-melanistic, having brought stripes but retaining a striped pattern. It has been suggested but not conclusively proven that black cougars might also exist.
Perhaps the most widely known melanistic cat is the so called 'black panther'. this is not a species at all but a name applied to the black/melanistic forms or any large cats, most commonly the jaguar or leopard. A black cougar, if it can be proved to exist, would also be called a black panther as the cougar is a panther species.
Melanism in medium to large sized cat species attracts particular attention from cryptozoologists because there are persistent sightings and rumors of large black cats sited in areas where none are known to be endemic (for example in the Untied States and United Kingdom). Some groups believe black cougars exist in areas such as Michigan. However the only photographs being circulated could easily be common domesticated cats captured in a manner that makes their size difficult to judge.
Fair Game Pheasant Farm has this example (shown right) of a completely black male. Other examples can be seen at Three Creeks Farm.
The Thing About Peppered Moths
In the introduction I briefly mentioned the different color morphs of peppered moths (Biston betularia). Many people will have been taught in biology class that the industrial revolution caused the black forms to become more common because they were better camouflaged on sooty surfaces and so could avoid predation from birds.
There was a period of skepticism as this argument was based on some false assumptions and illustrated with stage photographs. However, more recent research has largely vindicated the idea of the rate of melanism in this species being strongly influenced by selective predation.
- Melanistic and Leucistic Birds - a set on Flickr
Flickr is almost certainly the best online photo management and sharing application in the world. Show off your favorite photos and videos to the world, securely and privately show content to your friends and family, or blog the photos and videos you
- Texas Cryptid Hunter: The Black Panthers of Texas: An Impossibility?
- B. S. Grant, D. F. Owen, and C. A. Clarke (1996). Parallel Rise and Fall of Melanic Peppered Moths in America and Britain. Journal of Heredity, 87, 351–357..[pdf]
- Cook, L. M., Grant, B. S., Saccheri, I. J., & Mallet, J. (2012). Selective bird predation on the peppered moth: the last experiment of Michael Majerus. Biology Letters, 8(4), 609-612. [html]
- Nachman MW, Hoekstra HE, D'Agostino SL. (2003). The genetic basis of adaptive melanism in pocket mice. PNAS, 100, 5268-5273. [pdf]