What is an albino? How can there be so many types of albinism in reptiles? I thought albinos were always white? All of these questions stem from a fundamental difference in the ways pigmentation are displayed between mammals and reptiles. In mammals, there is only a single chromatophore, the epidermal melanocyte. Therefore, if it fails to function properly, any 'albino' is all-white. In reptiles, there are three types of chromatophores present. This explains the numerous types of 'albinos' present in captive collections today.
These cells synthesize and contain black and brown pigmentation known as melanin. There are two kinds of melanophores present, dermal and epidermal. Dermal melanophores are located in the upper dermis, while epidermal melanophores are located in the lower epidermis skin layers.
The process of creating melanin is fairly simple. Tyrosine, which is a type of amino acid, is converted into dopa, and then into dopaquinone in the presence of tyrosinase, which is synthesized by the melanophores. Dopaquinone is later modified into melanin and deposited in the appropriate melanophores. This is the root of the terms 'Tyrosinase-positive (T+)' and 'Tyrosinase negative (T-)' albinos.
In T- albinos, tyrosinase is not produced by the melanophores and no melanin is ever created in the melanophores. The result is an animal possessing absolutely no black or dark brown pigment whatsoever.
In the T+ form of albino, tyrosinase is produced but is blocked from gaining access into the melanophores. Simply put, all the parts are there - they just can't mix. However, in most specimens there is a certain amount of 'mixing' that occurs by cells disrupting or possibly by osmotic transfer. The exact method is unclear, and may vary. What is clear is that T+ albinos are generally darker than their counterparts, often containing traces of melanin deposits that result in a slightly darker look than the T- albinos of the same specie. Often red coloration is particularly prominent and many times the eyes are dramatically darker than expected.
These chromatophores produce red and yellow pigments known as pteridines. These may vary in color from pure yellow to pure red, as well as intermediate shades. Xanthophores possessing a predominantly red coloration are referred to as erythrophores.
Xanthophores also retain yellow to reddish pigments contained in the diet in the form of carotenoids. Carotenoid retention continues throughout life, and intensity of pigmentation varies based on the quantity and types of carotenoids contained in the diet. Additionally, the animals' genetic predisposition towards and ability to store carotenoids will affect appearance.
Iridophores, unlike the other two types of chromatophores, do not produce pigments. Instead they contain deposits of purines. These deposits are crystalline in nature and reflect varying amounts of light. The way the light is reflected is determined by the type of purines and the way the crystals are oriented. These structures control the appearance and reflection of green, blue and red light to our eyes. The primary forms of purines in reptiles are guanine, hypoxanthine, and adenine.
Iridophores appear to be most concentrated in areas lacking melanophores and may play a role in blocking harmful UV radiation contained in sunlight.
This area is under construction. Check back soon to learn more about chromatophore biology in reptiles. We will try to complete it soon, but the breeding season is upon us!