Previously I wrote about melanism (http://on.fb.me/1ToI4db), amelanism also exists and is characterised by a lack of melanin pigments (making it the opposite of melanism). Melanin is a pigment produced from an amino acid by a melanosome. Amelanism can affect a range of animals including fish, mammals, birds, and amphibians. However, difficulty in producing melanins affects these groups of animals differently.
In mammals, if a melanosome is unable to produce melanin, no pigment is produced. As such, the mammal has white hair, pink skin, and pink, red, or violet eyes. Hair is affected by the lack of melanin, as in a normally functioning melanosome, melanin is produced and then engulfed by a cell. When this cell happens to be at the root bulb of a hair, the hair takes up the melanin pigment.
In other vertebrates such as fish, birds, and amphibians however things happen a little differently. These vertebrates produce a wider range of pigments via chromatophores (for example xanthophores produce yellow pigment, erythrophores produce orange pigment, and cyanophores produce blue pigment). Therefore a lack of melanin affect pigmentation differently, so amelanistic vertebrates are less likely than mammals to have pale skin and red eyes.
Got a closeup of some Doryteuthis pealeii hatchlings! Chromatophores are the cells responsible for the color changing camouflage in cephalopods. You can see that one of the hatchlings has the chromatophores on its head activated, showing yellow (xanthophores) and maroon pigment (erythrophores), while the other squid has inactive chromatophores (dark dots).
Chameleons are some of the most brilliantly colored animals on the planet. But how did they evolve the ability to change color?
Scientists used to believe that chameleons changed color by spreading out pigments in their skin, much like octopuses or squid do.
The top layer of chameleon skin – called the epidermis – contains yellow pigment cells called xanthophores, and red pigment cells called erythrophores. But the amount of pigment in the cells stays the same, even when the chameleon changes color.
Just beneath the chameleon’s skin is a layer of cells called iridophores. These cells contain microscopic salt crystals, which are arranged in a three-dimensional pattern like oranges stacked on a fruit stand.
When light hits the crystals, some wavelengths are absorbed and some are reflected. The result, to our eyes, is the beautiful rainbow of colors on the chameleon’s skin. But what we’re actually seeing is light that is bouncing off of these tiny crystals. What we perceive as green, for example, is blue wavelengths of light being reflected off the crystals and through the layer of yellow xanthophore cells in the chameleon’s epidermis. The result is bright green skin that contains no green pigment!
The process of changing color is called metachrosis.
DEEP LOOK: a new ultra-HD (4K) short video series created by KQED San Francisco and presented by PBS Digital Studios.
Explore big scientific mysteries by going incredibly small.