How much line breeding is too much?

The place where I see line breeding being a problem among reptiles is, if one of the original subjects carries a defective trait, i.e. Spider Wobble, Desert Females, making it susceptible to a disease or abnormality, then one might consider that the entire line would be predisposed to the same. In the Hobby everyone has come to expect and accept that Spiders have a wobble, though in varying degrees of severity. But, what if the anomily was something viral, versus neuroligical? If a virus came along that infected the original subject and where fatal, one might expect the entire line to succomb to the disease. Potentially a lot of snakes could be lost in a short period of time. If you want an example look up "White Nose Fungus" among bats. They say it may make extinct, the little brown bat in a decade or less, if they cant find a solution.

On the other hand, those subjects from the line that didn't succomb, if any, would continue the lineage, and the line would be stronger for it. Straight up Darwinian Theory, survival of the fittest.

I'm not saying that line breeding reptiles is always safe regardless of how many generations, but I believe it would take significant inbreeding to get to a place where you could point it out as "the" problem.

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Originally Posted by Spoons

I see absolutely no reason why reptiles would be any different than any other animal. Yeah, they're a different type of animal with different genes, but crossing back those genes too much reliably causes problems.

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You can't make a blanket statement like that, crossing back a lot creates high homozygosity animals thats all. Now that can cause problems if there are negative recessive or polygenic traits to be brought out. If there is not, you create animals that can reliably have zero issues. Bringing in new genetic could actually be the downfall to a project, depending on the new genes brought in.

I don't even see a difference between mammals and reptiles, look at many peoples rat colonies, focusing on high production zero issue rats.... eventually you selectively breed out the issues and just have healthy rats that don't have issues anymore and as a bonus make lots of babies on average. Unforchantly I feel behind on production and haven't caught back up so I have all sorts of random rat genetics now as I had to buy more. I didn't realize how good I had it with my inbreed rats.

It just happens that humans (everyone favorite thing to compare) seem to have a lot of negative traits on average, so hooking up with your close family will more than likely cause problems statistically. It's not to say you couldn't eventually breed out human genetic problems either, just would take an enormous amount of time and im sure theres issues with ethics of it also.

Look at a ball python and angolan python.They more than likely had a common ancestor that had two different paths of inbreeding to create the two species we have today. I think it would be silly to assume multiple paths lead to the exact same animals we have today. There was also more than likely many failures they are not around anymore.

Inbreeding can make stronger animals as it can make weaker ones, homozygosity just tends to make traits more extreme one way or another.

"Now that can cause problems if there are negative recessive or polygenic traits to be brought out"

This is spot on. And you're right, you could have no problems at all. I agree that, as least from immediate glance, problems are less common in reptiles- but I guess I don't care to risk it.

Great things have been done with line breeding. No arguments there. But it is not foolproof and not without it's faults is all. :) I should maybe not have compared to humans - it is definitely something that has piqued my interest. I'd like to dig more into it when I have the time!

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Originally Posted by Spoons

"Now that can cause problems if there are negative recessive or polygenic traits to be brought out"

This is spot on. And you're right, you could have no problems at all. I agree that, as least from immediate glance, problems are less common in reptiles- but I guess I don't care to risk it.

Great things have been done with line breeding. No arguments there. But it is not foolproof and not without it's faults is all. :) I should maybe not have compared to humans - it is definitely something that has piqued my interest. I'd like to dig more into it when I have the time!

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I just don't like the demonizing of it, "the risk" is completely fabricated by people blindly against inbreeding. Sure you can find scattered accounts of negative traits showing up when inbreeding, but there are accounts of them showing up in unrelated animals also. If you are breeding responsibility, you would work to remove the negative traits, inbreed or not. Breeding in general is not foolproof and without faults and you don't have to look far to see that.

All line breeding does is concentrate genetic traits. Which is exactly what it's intended to do. There is no such thing as too much or too little. If the genetic trait is detrimental to the individual, then it's bad. If it's advantageous, then it's good. And there is no way to determine which it will be, if any, until the cross has been made.

If there were no line breeding, we would have virtually no morphs and everyone would only have normal 'wild type' ball pythons.

Not that I'm any kind of expert but OWAL and Mark have it spot on couldn't have said it better myself.

My my theory on humans having so many negative genetic traits currently is due to the very short amount of time (relative to other genus) that we have been around. Add in the fact that our species got lucky with the brain traits we have allowing us to master the food chain and you can see how our negative defects never really got a chance to be selected out. Humans had it very easy historically compared to every other species out there. The brain really got us into a position where we had abundance and therefore we do not have as direct of a Darwinian pull against negative traits. Even before civilization we had much better lives then most other species.

I know this post is a month and a half old, but its exactly what i was wondering myself, among other things. ;)

I understand that lower order animals tolerate inbreeding far more than do higher order animals.

do you see anything like reduced clutch size or infertility if too many generations are inbred?

Say, brother and sister breed, then breed dad to daughters, mom to a son, then keep crossing and crossing?

Is that typically avoided simply because people move on to more complex designer morphs, thereby outcrossing by default?

Is there any value to holding an animal out for a few years, then breeding, so the genes haven't been in the pool for a while?

Or (if one isn't an absolute anti-inbreeding fanatic) does it really not matter?

I work with a practically extinct breed of dog and our struggle is that there is so few of the breed that there is not enough genetic diversity. We avoid inbreeding/line breeding as much as possible to try to build diversity. Unfortunately, generation after generation, breedings begin to bottle neck and you end up crossing lines. In dogs, inbreeding once won't nessesarily cause an issue but multiple line breedings will make genetically weak dogs. I'm new to reptile genetics and many veteran BP breeders have said that it does not have any effect so I would listen to them. For my projects, I am going to attempt to reach my goal without any line breeding because Id like to believe, like dogs, outcrossing lines equals a more genetically solid animal. Of course those are just my practices so I'd recommend you listen to the more experienced reptile keepers

What breed, alittlelssbutter?

Mammals are more complex, so I can see where more would be able to go wrong.

I bred fruit flies for my dart frogs for 4 years or so from only two original cultures. I got about 48 generations out of each. Never a drop in production, or (that I saw) physical defects like one wing, no eyes, missing legs, etc. However, the flightless flies DID evolve the ability to fly!

Snakes are much less complex than are dogs.

I can only think of it being like a radio flyer vs a harley full dresser. Many more parts on a harley than a red wagon to go wrong.

Kai Ken