The effects of mutations in rats - Albinism
All of the genes that cause changes in our rats away from the smooth coated, top eared agouti are mutations. Many discussions occur regarding whether specific mutations are in the best interests of the rat or not, most notably hairless, tailless, rex, and albino. The subject is emotive and raises issues for breeders and owners as to whether there are varieties that are better not actively bred/sought after. Having inherited my daughter’s still infant ‘line’ of pink eyed whites (PEWs), I found myself in the unenviable position of having to decide whether I should carry on breeding them, and decided to try to impartially investigate the effects of albinism in order to make a decision.
Albinism is a hereditary mutation in which the animal doesn’t produce the usual melanin that is responsible for pigmentation of the skin, fur and eyes. Melanin has two major functions in wild rats; protecting the eyes (and other vulnerable areas) from damage from UV radiation, and camouflage. Clearly camouflage is not an issue for pet rats, indeed some albino rats would be better camouflaged in human driven environments than agoutis, but since they have no need to blend in with their surroundings this is unlikely to affect them. The issue of how UV light affects non-pigmented eyes is one which has been widely studied and seems to be quite well understood.
The effects of albinism on vision
At the back of a pigmented rat’s eyes the retina is made up of a layer of photo receptors (which are stimulated by light) and over the top of these is a layer of epithelium which contains the pigment melanin. This also absorbs light and prevents light from ‘bouncing back’ and stimulating the retina more than once. Signals from stimulated photo receptors (cones and rods) are then transmitted to the visual area of the brain, where they are processed. Albinism removes all of the pigmentation from the eyes which leads to a range of visual problems from reduced acuity and depth perception to degeneration of the retina itself due to overexposure to light. Albinos also have a significantly smaller visual pathway (the nervous system link from the eyes to the visual centre of the brain). It is extremely likely that by a few weeks of age (and with exposure to normal levels of daylight) albino rats have extremely poor vision. The blurry world of the pigmented rat will have become increasingly blurry, with little perception of depth and movement. Their vision is also quite ‘flooded’ with light, so that normal light can dazzle. It is likely that some mature albino rats have such poor vision that they are effectively blind.
The other senses
There are two studies that seem to suggest that rats might have a reduced sense of smell. However, there are many others where albino rats have been used for ‘smell-experimentation’ which seems unlikely if they have any significant impairment. One of the studies that suggested impairment showed that albino rats seemed to display a reduced aversion to raw garlic. But there could be other reasons why this was so, not just lack of smell. Hearing and whisking appear to be normal in albinos.
Because sight is not the primary sense in rats it is unlikely that albino rats feel the effects of albinism as acutely as albino humans (who also have psychosocial aspects of the condition to deal with). Probably because of this, what is viewed as a ‘condition’ in humans is considered no more than another colour variety in rats. However, it is not realistic to say that rats do not use sight enough to be diminished by the loss of it. Maze experiments (amongst others) have clearly demonstrated that rats rely heavily on visual clues to find their way around.
Albinos in laboratories
In researching this article I found myself asking the question “Why albinos?” in relation to the predominance of this variety in laboratories. Even after reading a bit about the history of the Wistar Institute and the beginnings of the use of albino rats for experimentation I was unable to answer this question. I wondered if it might be due to some perceived docility in relation to agouti strains, but could find nothing on this subject.
Each of us will need to draw our own conclusions about whether any mutation is a mutation too far. The PEWs I have known personally span the whole spectrum of rattie temperament, from docile and loving, to easily spooked and cautious, to cheerful, outgoing and bombproof. I cannot find noticeable disadvantage in all PEWs but I do think that where vision is so poor as for the rat to be considered blind, there do seem to be differences, and my human behaviour around them needs to be modified in response. These rats often seem to be easily surprised if they don’t hear me coming, so I make a special point of speaking to them and touching them gently before moving to pick them up.
The ‘lab to wild’ experiment at http://www.http//www.ratlife.org used albino rats, and they clearly adapted well to their new environment without noticeable disadvantage (other than their colour made them very visible!) I would, however, (personally) become uncomfortable about adding in further mutations like hairlessness and rex, that would decrease the information available to them from other sense organs as well.
Articles related to breeding rats.
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