Thoughts on novel mutations through selective breeding?

[user 7388]

Ok, hear me out.

In 1892, Wilhelm Mucke started trying to breed a white rabbit without red eyes. Reportedly, he started with breeding Dutch rabbits, and once he crossed them with the white varieties of Flemish Giant and Holland Lop he managed to get a pure white rabbit with blue eyes. He presented this in 1907 as the Vienna White. Now we know that the V locus controls the Vienna gene, separate from both albinism and Dutch, which created Vienna-marked rabbits in heterozygotes (that are similar to Dutches in some cases) and BEWs in homozygotes (although this gets covered by homozygous albinos.)

Another known example of this occurring is when the Lionhead rabbit was bred. Reportedly, mini Swiss Fox rabbits were bred to the Netherland Dwarf/Hermelin breed of rabbit. The Swiss Fox was a long-haired rabbit so I presume it was an angora genotype, ll. The ND is a dwarf rabbit, Dwdw. When bred together a novel mane gene arose that we know call M. Heterozygotes are single-maned, homozygotes are double-maned. This is also a dominant mutation, and like Vienna, is separate from angora or dwarfism. We can breed llMM rabbits (which is just too much wool if you ask me) and maned rabbits are starting to appear in full size, for example in European NZ meat herds. There's also the Belgische Bartkaninchen breed.

But people also cross/mix rabbits all the time and don't spontaneously cause new mutants. What could the X factor be?

I'm interested in the possibility of green-eyed rabbits. Blue eyes come from a lack of eumelanin produced in the stroma, causing the light to refract in the eyeball off the epithelium (which still has eumelanin pigment) and appear blue, for the same reasons water and air appear blue (they aren't actually pigmented blue!) Albinism causes no eumelanin in the epithelium either, so the light is reflected off the blood, hence red eyes. Lutino, from what I can gather, retains some pigment in the epithelium but to a lesser degree, hence pink or in some cases lilac. Now in humans, then the stroma has mild eumelanin pigmentation instead of full, we get hazel eyes; the brown affects the blue refration to get an in between. In rabbits that seems to appear as blue-gray instead, potentially due to the different structure of the eye. But in humans, when the stroma is pigmented by pheomelanin instead of eumelanin, we get green eyes.

Rabbits, of course, have eumelanin and pheomelanin too. That's where the coat colours come from. I would hypothesize that if a mutation occurred which cause the stroma to be pigmented by pheomelanin instead of eumelanin, a novel green (or possibly yellow-green given the different structure?) eye phenotype would occur.

The E locus affects the MC1R gene in such a way that dominant mutations overproduce eumelanin and recessive extensions produce none, so the melanocytes default to pheomelanin, at least in the coat. This doesn't seem to extend to the eyes though as non-extension red/fawn/cream rabbits still have brown eyes. Could a further recessive E locus mutation cause eumelanin production to cease in the stroma?

The C locus turns off pheomelanin production, leading towards albinism as we trend towards more recessive mutations. But hypothesize a super-dominant mutation on the C locus: could it result in an overproduction of pheomelanin? Say, in the stroma? That, paired with something which limits eumelanin in the stroma, could leave a stroma only pigmented with pheomelanin.

The B locus weakens eumelanin. Some people report young chocolate rabbits to have green eyes. This is probably more akin to hazel than true green, but following the trend of the creation of Vienna, it does seem that selecting for nearly-correct phenotypes with selective breeding can spontaneously trigger the desired mutation. Not sure what selective pressure would help that (reduced eumelanin in the stroma can lead to increased eye sensitivity in full sun, so perhaps darkness could provide pressures for lighter coloured eyes? In human history, moving north seems to correlate with lighter coloured eyes) but chocolate rabbits might be part of the solution.

Of course people have already been breeding chocolates, non-extensions, non-extension chocolates, and more. These mutations haven't spontaneously occurred that we know of so far. Whether it ended up being a mutation limited to an existant colour locus and thus was limited to a certain phenotype, or mutated in a new locus (allowing us to backbreed green eyes to any colour rabbit), I feel like this could end up a valuable pursuit.

Curious to get feedback on my line of thought here and if anyone knows anything more about this stuff that might help. Thanks!

 

[Zass]

In a lot of those traditional breeding projects, extensive line breeding and often strait up inbreeding for many generations was common.

Perhaps that's your missing factor? While rabbit breeders do lightly or occasionally inbreed or linebreed, it's almost never to the extent that was routinely done in the past.

Public opinion has steered people away from it, despite research that suggests that rabbits can be inbred for many generations without genetic harm.

 

[user 7388]

That's a good point Zass. I do plan on doing some linebreeding in my breeding program over the coming years to reenforce my desired phenos, so maybe I'll get lucky. I've heard linebreeding is safe to ~7 generations if you start with healthy rabbits but that would be ~7 years (maybe half if I do winter breeding indoors) to get to the point where mutations might occur. Perhaps I'll push the common accepted practices these days and do some direct inbreeding... I'll probably just end up with detrimental health conditions, but you never know! Thanks

 

[Zass]

I think, the point of mutation is very likely to be exactly where "genetic harm" is occurring. What you are describing would not be a project for anyone at all faint of heart.

You would have to be ready to cull everything "off" and possibly the lines that produced it too.

Otherwise, you could easily end up causing more harm than good. Doing it responsibly could mean losing the whole project if things go south.

(For example, if you end up causing a genetic predisposition towards cataracts, it would be better to terminally cull the entire line that produced them rather than to pet them out, and let them potentially introduce those harmful genes into the general population..)

 

[hotzcatz]

There very well may be rabbits out there with green eyes. How many people take their rabbits out and about?

They wouldn't be taking them to a show table unless green eyes were a 'breed standard'. By requiring certain colors of eyes in breed standards, that's gonna keep some breeders from trying for them and actively breeding against them if they do show up.

There's also quite a bit of pressure on folks to follow breed standards, too. Folks selling a show prospect can get $$$$ (or €€€€, ¥ ¥ ¥ ¥, etc.) while the person doing cross breeding or whatever to get their mutations can only sell to the pet or meat market at merely a fraction of the price.

 

[user 7388]

Yeah, I'm sure a lot of people get into rabbit genetics in order to improve their breed and show rabbits but I'm the opposite. Just like I'm not a fan of purebred dog breeding (mixed breeds are so much healthier and unique! Purebreeding for function/attitude like with working dogs is different because you don't necessarily cull physical traits, selecting for aptitude mainly, so that's ok!) I think breeding for show is probably going to hurt the domestic rabbit gene pool over time (caveat being exceptionally responsible breeders who meticulously track all their bloodlines, I suppose.) Of course this somewhat conflicts with the idea of selectively breeding in order to cause novel mutations or wanting to breed a unique line of your own rabbits!

But I suppose the difference there is culling off-type show rabbits is, as you say, a good way to miss novel mutations. I was reading about Lutino the other day and if the guy who was breeding the orange rabbits had simply culled out the rabbit that appeared with pink eyes instead of breeding it back and expanding on it, we might not have Lutino rabbits right now. Now Lutino might not actually improve fitness for rabbits all around, but as a breeder, I'm still intrigued by it and wouldn't have wanted to see it culled. But with the mane and Vienna genes those breeders were intentionally crossing out rabbits (which should improve fitness) in order to come up with something unique, so that wouldn't happen while breeding for show at all.

The other aspect of selective breeding I'm very intrigued by is breeding for aptitude like with working dogs, or maybe more similarly, breeding for tameness like the Belyayev fox domestication project. One of the things I'd like to do in my herd is start breeding only the friendliest rabbits, and then get more rigorous about what I accept in personality for a breeding. I'm very tired of getting clawed up when I have to pick up a rabbit; selecting for the rabbits that are the calmest about being picked up and don't kick--to the point where you could get a tame enough rabbit that it rarely or never kicks even--will likely have such a reductive effect on adrenal response that we could see novel phenotypic changes as a result of biochemical pathways being altered, as was the case in the fox domestication project. Of course foxes, like cats and dogs, aren't prey animals so it just might not be possible to achieve that. Still, some of my rabbits come right up to me in my hutches and nuzzle my hands and face when I get down on their level, and others flee to the back of the cages. Obviously selecting for rabbits that want attention and loving will have a positive result in my rabbitry, even if it doesn't cause a novel mutation. Of course, selecting for that as a primary selective pressure means throwing phenotypic selection out the window, which is why some fancy breed show rabbits are naturally very flighty, because you have to select for phenotype over personality (although again I'm sure the best breeders manage both.)

I'm still only in my second year of rabbit breeding so I've got a lot to learn still, practically (when reading articles ceases to help) but I'm excited by the prospects moving forward.

EDIT: Oh, and Zass, you're totally right. If genetic disorders crop up you'd have to cull extensively. It's a tough job. That's why I was intrigued about the mutations which came up from outcrossing rather than inbreeding!

 

[hotzcatz]

Temperament will breed true. It's one of the criteria when deciding which bunnies to breed. The ones here are English angora and they're selected for fiber quality, health, temperament and possible coat colors. We do try for ARBA conformation but that's pretty far down the list.

With the coat care requirements of an English angora, we can't have bad tempered rabbits.

There's variations within each genetic characteristic. With breeding selection, it wouldn't be hard to skew the characteristics towards one end or the other.