Interesting Deformed Bearded Dragon Hatchling

This baby dragon was found dead still inside his egg on January 2nd, 2005. I thought this was a very interesting case and decided to post these photos here for the interest of others.

This hatchling had been able to slit its egg shell and get only his mouth and nose out before it expired. Upon discovery, the hatchling was removed from its egg for examination and to determine cause of death.

Note the following abnormalities:
1. tail is completely lacking
2. body and neck are markedly enlarged
3. right nostrol communicates with the mouth and there are no teeth on rostral (nose) end of the maxilla (upper jaw).
4. Both rear limbs are dysplasic (deformed), the left rear food has an extra digit (polydactyl) which is much larger than the rest of the digits on this limb.
5. The "cloaca" (or what looks like one here) does not appear to have a true opening to allow for defication.

"His" (sex could not be determined due to lack of cloaca) parents are a pair of Sandfire het Leucistics. No other offspring have shown any deformities, either in this clutch or older sibs. This is believed to be a fluke. I plan on performing a necropsy in a few days to see the state of the internal organs.

It is assumed that if this hatchling would have survived the hatching process it would have required euthanasia or eventually succomed due to lacking a true cloaca.

<img src="http://therasdragon.splunk.net/BDs/Deformed/deform4.JPG">

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<img src="http://therasdragon.splunk.net/BDs/Deformed/deform1.JPG">

<img src="http://therasdragon.splunk.net/BDs/Deformed/deform2.JPG">

<img src="http://therasdragon.splunk.net/BDs/Deformed/deform3.JPG">

<img src="http://therasdragon.splunk.net/BDs/Deformed/deform6.JPG">

<img src="http://therasdragon.splunk.net/BDs/Deformed/deform7.JPG">

If the above do not display visit this link:
http://therasdragon.splunk.net/BDs/Deformed/deform.php

Because the parents were het for Luecistics the cause of deformity most probibally is due to inbreeding. Any time you are working with a mutation it means that all animals originated from one. The only way to ensure a good captive population over several generations is to only breed the very best and healthiest from every clutch with as distantly related animals as possible.

Craig

Statistically this deformity cannot be assigned as a genetic deformity. Let me explain.

Imbreeding only INCREASES the likelihood that genetic defects will occur. It is not at all a certainty.

First off, BOTH parents have to be carriers for the defective gene. On average full siblings only have 25% of their genetic makeup in common. So let’s say that your dad has a gene for purple hair, he didn't have purple hair cos it's a recessive gene. Now you get 50% of your DNA from mom and 50% from dad. Each child your dad has that means has a 50% chance of getting the purple hair gene. So you had a 50% chance and your sister had a 50% chance, meaning you have a 25% of BOTH having that gene.
Now how about cousins? Even more complex, I'll try to make this simple. Let’s say you win the lottery here and both you and your sister have the purple hair gene. You each have a child (not with each other). Your child has a 50% chance of getting your purple hair gene. Since you had a 50% before you multiply those together. 50% X 50% = 25% chance that your son will inherit the purple hair gene that your father had. And same would go for your sister's child.
Now lets say we live in the boonies, your son marries his cousin from your sister. They each had a 25% chance. You multiply their chances together to figure out the chance that BOTH have the purple hair gene. 25% X 25% = 12.5%. There is a 12.5% chance that two cousins will have the same purple hair gene.
So what do these percentages mean? With each successive generation apart there is less and less of a chance that you'll end up with parents with the same defective gene from ol' gran-pappy. By the time you get to 3rd or 4th cousin, the chance is about the same as you having a kid with Suzi-Q from your freshman English class in high school (unless your sister was Suzi).

So now we know the CHANCES of the parents having the same gene. What if they do?

If a birth defect, or any defect at all, comes from genetics and is a recessive trait (as it would have to be otherwise the parents wouldn't have had tails, and yep they do) we would see 1/4 of the offspring from normal parents displaying this trait. Wait this sounds familiar... it's just the same odds as we see with getting leucistics from two leucistic hets. huh, why is that? A child has a 50% chance of getting it from mom, and a 50% chance from dad. 50% X 50% = 25%. So that means if mom and dad BOTH carry it we should SEE 25% of the babies without tails.

Now a bit of family history on my pair. They have produced over 70 babies, this is the one and only defective baby produced. 1/70 does not equal 25%. Hmmm... so statistics tells us that this is probably not genetic.

Can someone be born with something that's not genetic? Of course. It actually is the NORM. MOST genetic defects of this kind (extreme deformities or aplasia of limbs) are NOT genetic. Congenital deformities, those present at birth can be caused by a number of factors, the least of which is genetics. More commonly they are caused by problems associated with development of the fetus itself. Problems caused by everything from hormone imbalances, dietary deficiencies, drugs or toxins, as well as plain and simple bad luck. There are many examples of such non-genetic deformities in people. Heart-valve deformities, spina bifida, camel toes, birth marks, etc.

So what am I getting at? Let’s recap.
First the chances of two individuals from the same family having the same gene decreases drastically over generations.
Second, genetic deformities caused by a recessive gene should show up at a frequency of 25% within the same pairing.
Third, most congenital defects (aka those present at birth) are not genetic.

So how does this apply to this case?
The parents are 1st cousins, thus they had a 12.5% chance of carrying a defective gene IF and ONLY IF one existed in their family tree. WAIT! What do I mean IF? That's right. The gene has to be in the family first. The chances of that are extremely slim to BEGIN with.

So how do genes get defective? Mutation. For the most part most bearded dragons aren't smoking cigarettes or soaking themselves in one of the many carcinogens that can cause genetic mutations. So it HAS to happen completely at random. I sadly do not have the base rate of genetic mutation under normal circumstances memorized for this posting, but I'll let you know it's extremely and I mean extremely small.

Ok, let’s get back on track here.
If you were told you had a 12.5% chance of surviving, would you be optimistic? Well we'd want to be, but reality would point more to no. 12.5% is not something to bet on, unless you LIKE losing money.

Do we see evidence of a genetically inherited defect IN this pairing? YES. Is it what this baby had? NO. He wasn't leucistic :P.

So how come imbreeding isn't practiced more heavily? One thing that has been proven to be caused by imbreeding is what is called "decrease in hybrid vigor". As a population gets more and more inbred, more and more of them have pairs of completely identical genes in their DNA. This is called homologous pairs. For some reason animals with MORE homology are less hardy than those with very little. That's why mutt dogs typically have fewer problems than pure breeds. That's why nearly extinct species like Pandas and Cheetahs aren't very healthy animals.
BUT... this requires massive amounts of inbreeding generation after generation.

So what does this mean to the bearded dragon breeder?
It is OK to inbreed some, as long as you understand the risks and can recognize a problem (I.e. know how to spot a problem using statistics). If at all possible outcross your lines to maintain hybrid vigor as much as you can.

For more information on this subject read the following:
1. ANY college level Genetics and/or Embryology text - this will explain the basic concepts of inheritance and development as well as imbreeding principles.
2. Thomson's Special Veterinary Pathology, 3rd Ed. by William W. Carlton and M. Donald McGavin (this explains congenital defects and their causes, as well as how UNLIKELY they are do to genetics).

I hope this helps clear up the misconception that birth defects are CAUSED by imbreeding and if they ever appear, BLAME it on that.

that would be so much less complex if you used punnett squares

Just a small aside... the entire captive population of Bearded Dragons in the states is descended from the small number of stock animals that were present outside of Australia when the export ban went into effect (and a few which have been smuggled out since; largely ending up in europe). Off the top of my head I do not have an exact number for the source stock but I *believe* I remember reading numbers from a few dozen to around a hundred. Every captive bearded dragon outside of Australia is about as inbred as you can get. Individual morphs which may trace their roots back to stock found within that breeding population which have been more specifically and recently line bred aren't really any more or less likely to display a defective genetic trait (if not specifically linked to the phenotypical anomoly) than buying two random "unrelated" animals from different sources.

I also generally pitch in the fact that inbreeding can't actually add anything to a gene pool- it merely exponentially strengthens the traits for which a genetic basis is already present. Not everything comes down to simple mendelian genetics either... The point being that with genetically flawless (tough to define really given the subtle nature of generational evolution) base stock you could inbreed forever and never experience a single problem.

First, it's really had to type a punnet square and second, they're annoying.

You are right, inbreeding does NOT inprove your stock, it only can maintain a trait within a population. EXCESSIVE inbreeding however CAN hurt your stock because it decreases your hybrid vigor. You end up with animals with more homozygous pairs of genes, thus effecting their reproductive efficiency, their hardiness, their size and the symmetry of their skull. That is why when you line-breed (a type of inbreeding actually) you outcross in ulternating generations and breed then two offspring from two DIFFERENT outcrosses together to reestablish the gene in the case of a simple recessive gene like leucistics.

However, you have to be EXTREMELY inbred to end up with deformities of this severity being caused BY the inbreeding. Even Cheetas and Pandas aren't THAT inbred.

BTW the US pet and research gerbil population all descending from the same 6 originally imported animals. They are a completely closed population. No one is being imported at all, we're at least bringing in european stock in Beardeds. So we're not that bad off. And gerbils aren't seeing any problems as of yet from being as inbred as they are.

It's about doing whatever you do responsibly.

Now, I dare you to ask anyone who breeds reptiles on any scale larger than one pair if they've ever produced a deformed baby, you'll get a lot of yeses.
Does that mean they did something wrong? Maybe, but most likely it was just a fluke of nature. Which is what causes MOST deformities.

I am in no way BTW saying that inbreeding is a good thing. It's a risky thing. But as long as you understand the risk you are taking and act accordingly, that's what is important.

Seamus Haley - I really like your icon with the head banging on the computer. I feel like that everyday :P