Albinism in animals:

Have you ever seen an albino animal before? Ever wondered how an animal can end up being this white when every other animal within a certain species is dark? Well, here I will try to explain a little bit about albinism in animals, why they become white, and what effects it might have on the animal that's showing this abnormality.

Albinism is a rather seldom happening, and it is rare to see animals displaying this for several reasons. One of the reasons for this rare event is the fact that this is due to mutations that hardly ever happens, maybe just in 1/ 20000-50000 cases, the rate depends a little bit on what kind of mutation that is causing the albinism(Encyclopædia Britannica 2014). Second, although this condition can be inherited and transmitted to the next generation, this is not very likely, since albino animals usually have lower fitness and less chance of surviving.

So what is actually albinism?

It is a condition that's congenital, and animals that have this are displaying an absence of pigmentation in skin, hair/scales/fur, and also in eyes.This makes the skin pale(more like pink since the blood vessels give the skin some color), and hairs and fur look white. Eyes will also look red, due to lost pigmentation(Encyclopædia Britannica 2014). The reason for this is the absence of the pigment melanin, and this can be due to different things. A common reason for this is likely to be connected with Tyrosinase, an enzyme that catalyzes the process where melanin is synthesized from Tyrosine. With albinism this enzym might be defect or absent, and the result is absence of melanin that normally would give an individual color.(Encyclopædia Britannica 2014). Albinism is normally determined by homozygosity of recessive genes, but can also be determined by genes on the X-chromosomes(Redei 2008)

A bit about melanin production:

(Redei 2008):

During embryonic development precursor cells called melanoblasts move to the surface areas of the skin and become specialized cells called melanocytes.

Melanoblasts→ melanocytes

Melanocytes contain organelles that's called melanosomes were melanin is synthesized:

Melanosomes

↓

(Tyrosinase)

Tyrosine → Melanin.

Sometimes albinism can be a result of other things as well, and does not necessarily have to do with Tyrosinase. It might be that the melanosomes don't mature like they should, or that something else in the tyrosine-melanin pathway is defect. There is more than one enzyme contributing in this pathway, and defects can be found everywhere, because everything is dictated by genes, and genes are susceptible to mutations. But as mentioned, a defect Tyrosinase are very often the cause here(Redei 2008)

Why is albinism often decreasing fitness or making it harder for an individual to survive?

First of all albinism and the absent of pigmentation makes an individual more susceptible to cancer. Pigments acts as a screen against UV radiation, and protects the skin against damage(Encyclopædia Britannica 2014). When the animal doesn't have this protection, the damage caused by sun's radiation increases cancer rates, and rates of survival decreases. Second, some mutations that causes the albinism can also affect the eyes in other ways than just affect the eye's color. Albinism can give different eye diseases, either direct or indirect, that can effect an individuals survival(Witkop jr, 1989). Third, albinism effects defense mechanisms related to color and also camouflage. Imagine a white mouse running on the ground where it is seen against a dark brown background of dirt and leaf litter. It would be spotted hundreds of meters away, compared to a brown mouse with excellent camouflage. This mouse would literally advertise to predators where it is found at all times, and would probably not survive for long(see earlier blogs on this topic). Fourth reason for not seeing to many albinos in the wild can also be related to sexual selection. Sexual selection might exclude some albino animals if they don't show the desired colors that the other sex prefers. Then their chance of reproducing can decrease, and albino genes are then less likely to reach the next generation.

Under is some pictures of animals that are showing albinism.

Picture 1: Elks outside Oslo in Norway. Photo: Arnhild Oien

Picture2: How do you think this peacock do when it comes to impressing the ladies? 

References:

Witkop jr, CJ 1989, 'Albinism', Clinics in Dermatology, vol.7, no.2, pp.80-91, viewed 15 May 2014, <http://www.sciencedirect.com.elibrary.jcu.edu.au/science/article/pii/0738081X8990059X# >

Redei, GP 2008, Encyclopedia of Genetics, Genomics, Proteomics and Informatics, 3^rd edn, Springer, US.

Encyclopædia Britannica 2014, Albinism, Encyclopædia Britannica online, viewed 15 May 2014, <http://www.britannica.com.elibrary.jcu.edu.au/EBchecked/topic/12993/albinism >

Picture 1: Viewed 15 May 2014, http://www.bt.dk/utroligt-men-sandt/royal-albino-elg-faar-kongeligt-navn

Picture 2: Viewed 15 May 2014 http://animalshak.com/2012/09/wordless-wednesday-albino-peacock.html