# Congenital Defects...



## James D (Nov 17, 2008)

Ok, well this question is quite a specific one but I know (should I say hope?) there's at least one or two people that can answer it....

It's got to that time of year where every 5 minutes someone is posting about something hatching (I too am guilty of this). It seems as though each year there is a rise in the number of hatchlings with defects. I realise this is likely due to an overall increase in the numbers being hatched each year, so this is not what I'm asking about. I saw Andys thread about inbreeding depression and found that fascinating so it got me thinking....

I only really visit the lizard section of the forum so this mostly applies to them.

I don't think I've seen a 'sad news' thread yet where someone doesn't blame temperature fluctuations for the resulting deformity. I have a bit of knowledge about embryonic development but not enough relating to reptile embryology to answer my own question. 

How likely is it that temperature fluctuations are the cause of these deformities? 
I'm talking about when something hatches with only one eye/eyelid, an extra toe, or a limb missing. I realise that it is impossible to say by looking at an animal, what the cause of its disfigurement was, but I'm looking for an opinion on this from those with greater knowledge than me on the subject.

Sorry for waffling!


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## GlasgowGecko (Feb 23, 2008)

Hey James,

I have real mixed feelings, and some strong misgivings about the whole notion of temperature fluctuation controlling birth defects.

I fully accept that temperature plays a vital part in egg development, but would suggest that it is most likely to work between a relatively broad range of temperatures. The difference in temperatures responsible for sex determination for example would see a range of up to 10f. This makes me think that a 'fluctuation' in temperature would have to be relatively large, and sustained for a large amount of time.

This is not to say that it doesn't happen, but in my opinion it is more likely that it is either something else entirely, or in conjunction with another factor.
One potential here could be chemical imbalance, deficiency of certain trace elements could certainly be responsible for deformities of the eyes, and other organs.

Andy


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## xmashx (Sep 14, 2007)

this is helpful to me too. because when i got my Beardie i didnt know he had a birth defect. his liver was the wrong shape and size for his body. it would be helpful to know if its the breeders fault or somthing that you cant control.
xmashx


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## GlasgowGecko (Feb 23, 2008)

xmashx said:


> this is helpful to me too. because when i got my Beardie i didnt know he had a birth defect. his liver was the wrong shape and size for his body. it would be helpful to know if its the breeders fault or somthing that you cant control.
> xmashx


I'm sorry to hear that you had an issue with your Dragon, but I can say with certainty that we will never be able to confirm one way or another who is to 'blame' if indeed blame is the right way to look at it.

Clutch size may in fact have an effect on hatchling development with regards to resource partitioning before laying. This adds a further dimension to an already very difficult problem.

Andy


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## James D (Nov 17, 2008)

GlasgowGecko said:


> Hey James,
> 
> I have real mixed feelings, and some strong misgivings about the whole notion of temperature fluctuation controlling birth defects.
> 
> ...


Thanks Andy.

I had a feeling that temperature fluctuations were not the disaster everybody seems to think they are.
I have had temps swing by 8F (from 78 to 86 and then back) in a matter of hours and the babies have hatched out just fine. When I used to breed cresties the 'incubator' varied from 70-82F and I never once had a problem.

I would agree with you that dietary deficiencies (of the breeding female) are likely to be a potential cause that is often ignored. 

I just wish that people would be a little more open minded when it comes to these things. I think it is a complete waste of time reading through a lot of the threads regarding deformities as it is often just pages of people saying 'temps. fluctuated too much' or 'the parents were brother and sister'. I know that when I had 2 _S. williamsi_ hatchlings dead in the shell (one of which was deformed), they were the only responses I received!


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## GlasgowGecko (Feb 23, 2008)

The real fact of the matter is that it is just very difficult to tell what has happened. There are a variety of issues, and each is likely to be controlled by different factors.

If for example we take Polydactyl crested geckos. This is almost certainly (in my opinion) a genetic defect, not to mention a real worry. However something like a kink in the tail of a bearded dragon is much more difficult to delimit.

I also agree that it irritates me (perhaps more than it should) when people suggest things like temperature fluctuation as the cause for eye lid defects, suggesting that because it has never happened before it cannot be genetic. 

Andy


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## SleepyD (Feb 13, 2008)

James D said:


> I had a feeling that temperature fluctuations were not the disaster everybody seems to think they are.
> I have had temps swing by 8F (from 78 to 86 and then back) in a matter of hours and the babies have hatched out just fine. When I used to breed cresties the 'incubator' varied from 70-82F and I never once had a problem.


can only talk with regards to leo's but I have to say that I've found the eggs/babies a lot hardier then people give them credit for ~ my incubator suffered a power loss for several hours with temps plummating down to 70*F (was during that cold snap) ... of the eggs that were in it at the time I only lost a couple and had one hatchling with a stumpy tail (the tip had stayed in the egg)



> I would agree with you that dietary deficiencies (of the breeding female) are likely to be a potential cause that is often ignored.


*nods* I've always firmly felt that this has played a far more prevelant part in some problems then people think ~ mind you I also think this (along with breeding too young) is more responsible for duff/infertile eggs as opposed to 'infertile' males.



GlasgowGecko said:


> I also agree that it irritates me (perhaps more than it should) when people suggest things like temperature fluctuation as the cause for eye lid defects, suggesting that because it has never happened before it cannot be genetic.


I'm no genetic buff but I do think that genetics/faults play a far greater part in the occurance of eye/eye-lid deformaties then temps ~ I know some american breeders for instance will remove any leo with these problems as well as things like bug-eye's, kinked tails etc from any breeding program


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## GlasgowGecko (Feb 23, 2008)

SleepyD said:


> Im no genetic buff but I do think that genetics/faults play a far greater part in the occurance of eye/eye-lid deformaties then temps ~ I know some american breeders for instance will remove any leo with these problems as well as things like bug-eye's, kinked tails etc from any breeding program


Having re-read my post it seems to read like I was suggesting that it could not be genetic. This is actually the opposite of what i was suggesting. My point was more related to how people justify deformities inappropriately.

Without a doubt I would suggest that the occurrence of eyelid deformities (and others of this type) have increased within the captive population, and appear to have done so at much greater frequency than I would comfortably explain away with increased overall breeding activity. For this reason I would also suggest that there is a very good chance that this is genetically linked rather than simple nutrient deficiency (as is sometime suggested), however its exact nature is very unclear. Most tend to think about genetics as simple inheritance, but unfortunately this is most likely not the case, which again makes explaining the reasons why they should not breed doubly difficult.

The reason most large scale breeders will purge individuals with deformities, regardless of whether they are genetic or not is quite simple. If an external problem is present there may be further issues which you cannot see, which may also effect fitness in both this generation and the next.

Again, I have to say that I think the underlying problem here is prolonged inbreeding causing fixation of deleterious recessives, undoubtedly caused by small effective population size.

Andy


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## SleepyD (Feb 13, 2008)

GlasgowGecko said:


> Having re-read my post it seems to read like I was suggesting that it could not be genetic. This is actually the opposite of what i was suggesting. My point was more related to how people justify deformities inappropriately.


read fine to me which is why I said about genetics playing a bigger part then temps 



> For this reason I would also suggest that there is a very good chance that this is genetically linked rather than simple nutrient deficiency (as is sometime suggested), however its exact nature is very unclear. Most tend to think about genetics as simple inheritance, but unfortunately this is most likely not the case, which again makes explaining the reasons why they should not breed doubly difficult.
> The reason most large scale breeders will purge individuals with deformities, regardless of whether they are genetic or not is quite simple. If an external problem is present there may be further issues which you cannot see, which may also effect fitness in both this generation and the next.


I think it may be cases of either and or .....for example stunted growth isn't always inherited ~ it can also be down to either a singler genetic fault or nutritional deficiencies ~ however in some cases it can even be a combination of both with a genetic weakness being triggered or aggrevated through poor nutrition.
I agree that if external problem is there then there may well be further issues unseen in which case it's far better to remove from any further breeding.



> Again, I have to say that I think the underlying problem here is prolonged inbreeding causing fixation of deleterious recessives, undoubtedly caused by small effective population size.


*nods* taking this as the case then it would also lean towards weakened genetics/problems which could be triggered so to speak by other factors ..... really hope that made sense as most of what I learnt was 30+ years ago and is probably out of date lol


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## paulh (Sep 19, 2007)

When I was breeding corn snakes, my incubator was set to go to 90 Fahrenheit during the day. At night, the power was shut off, and the temperature slid down to the low to mid 70s F. I got good hatches with no deformities. So I am skeptical of the temperature theory, at least as the sole cause. 

Vitamin deficiencies in the parents are known to produce congenital deformities in vetebrates from trout to pigs and chickens. I see no reason why such deficiencies could not produce deformities in reptiles, too.

Genetics could be involved in causeing extra toes in lizards. My cat has extra toes, which is known to be genetic.


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