# question about split scutes *warning, contains "the birds and the bees" discussion*



## moswen (Jan 26, 2011)

i have been thinking lately about split scutes. i've tried to do some online research but i just keep ending up with the same answers: "it could possibly be genetic" and "it could be inconsistencies or too high temps during incubation," which i already knew those two. but even these two theories have holes in them, in m OP. if the temps or something else in the incubator was wrong, then all the babies would have split scutes, right? or if it was genetic, then more than just "one random baby every so often" would have them too, right? just my own personal observations and questions. i have a new question that i haven't been able to find that has been addressed anywhere:

could split scutes be a result of a sort-of "tortoise over-breeding" so to speak? not like it's harmful in any way to breed tortoises as much as we do, i'm not saying that at all, but i wanted to know if anyone has any information on about how often tortoises breed in the wild? in the wild, they live as solitary creatures, and rarely come upon other tortoises. so, it leads me to believe that they would mate WAY less in the wild than they do being in the same enclosure with 1 or 2 males and 2-5 females. this amount of breeding, while not seeming (and i don't personally believe it is) harmful in any way whatsoever, is bound to produce some less-than-perfect babies, i should think. 

(close your eyes for this next paragraph if you're not comfortable reading about the birds and the bees!)

so, my own personal thought process has led me down this path:

in human and beast alike, the best sperm always race to the finish line to be the first little wigglers to the egg, therefore ensuring the best possible chances for survival with the best possible candidates. as much breeding as a tortoise in the wild may do, compared to as much breeding as a tortoise in captivity may do, i have come into the idea that there must be more chances for a "less than perfect" little sperm to reach an egg. and since a female tortoise actually has the ability to with hold her eggs until the time and place is right, (up to three years i believe is the time frame) i now am disposed to believe that our females may be full up with as much sperm as they can handle, so because of that they expel as many eggs as they can get out of themselves at one time. 

now, because of that thought process, i've also begun to wonder if they might have the ability to choose, to a certain extent, which eggs to lay? like, say you have a batch of 15 perfectly formed and thriving little baby hatchlings, but one has a split scute. not to say that this baby has less of a chance to survive or is less healthy, but i could call it a "sacrificial egg," as in, laying so many "perfect" babies and one "imperfect" baby, in order to try to give the other babies the best chance at survival, with the one extra baby being given up to great numbers, in the chance that that baby will be eaten, sparing one other baby the chance of survival. 

we've seen it for sure in the inter-mixing of species, the two particular instances i am remembering are p.babcoki (sp?) breeding with p.pardalis (sp again?) and sullies bred with leopards, that the females can produce both pure species and the intermixed species in the same clutch. we've also speculated about "who's your daddy" lol, as in a single clutch of eggs from a female may have several different fathers, so this also helps me believe that a female may have the ability to choose which eggs she produces and when she does it. i believe that this would also help to keep the species as little inter-bred as possible, with releasing several eggs in the same clutch with different fathers, if two of those babies should happen to meet up again and mate, the chances of them coming from the same mother AND father would be less, so this would also help insure the survival of the species. 

now, this is all just simply my thought process and my speculations, i'm not claiming any of this for fact!! but i do want to know what you guys think about it though!


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## Greg T (Jan 26, 2011)

Wow Rebekah, that's a really in-depth possibility for split scutes. I suppose it could be genetic somehow, who knows. I've always believed it was simply cells that didn't quite do what they were supposed to do. Kinda like the mystery of some human imperfections like deformations and diseases. Certainly there could be more there though!!

Keep wondering and thinking because that's what finds solutions and cures in this world!


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## GBtortoises (Jan 26, 2011)

My thought on it: I think most split scutes can be attributed to low incubation humidity and gas build up in the nest site. Essentially birth "deformities" if you want to consider them as that. I have wild caught adult tortoises with and without split scutes and adult captive born tortoises with and without split scutes. Some of those adults with split scutes have never produced an offspring with split scutes and some of those adults without split scutes have produced offspring with split scutes. I think incubation temperatures, humidity and air exchange in the egg chamber during incubation play a part in a tortoise being born with split scutes. I have never seen one of my adult females, of any species, purposely choose a dry nest site. In fact, rain and warm tempatures are usually what triggers them to nest when and where they do when outdoors. Pretty much every nest that I have dug up has some degree of moisture in it. In most cases that moisture can usually be felt by touch. There is also almost always, at least 90% of the time, an air pocket above the eggs in an outdoor nest which allows for gas exchange and condensation collection. In rare cases I have had tortoises lay in a somewhat dry nest site only because there was not a more suitable spot for them at the time and the eggs had to be deposited. When I've had tortoises nest indoors the conditions are really not ideal. Their choice of nest site has been narrowed down to one spot for them. Sometimes not as deep as they'd like it and the soil, even though compacted, does not hold as true to form as that in an area outdoors that has usually been undisturbed and very well compacted naturally. Indoors they tend not to build the same nest cavity as they would outdoors. Whether the eggs are laid outdoors or indoors they all end up in an incubator. I used to have a lot more tortoises born with split scutes before I raised the humidity from about 60% up to nearly 80% that I strive for now. I still incubate at high temperatures to produce predominately female offspring (88-90 degrees) but between raising the humidity within the incubator and opening it twice daily for about 5 minutes at a time to allow for adequate air exchange, I very rarely ever have any tortoises born with split scutes anymore. So if it were genetic it would happen in spite of all of the above that I do.


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## matt41gb (Jan 26, 2011)

I really don't truly believe that it's genetic. If splits scutes were in fact "genetic," they would have to arise from some mutation that's been passed down through the same bloodline. Just because the parents have a split scute doesn't necessarily mean that a baby would be born with one. If the splitting of the scute happens during the incubation process, then it wouldn't pass on "split scute" genes to its offspring. If it were a genetic mutation, I would have to believe that a higher percentage of hatchlings with split scutes would be produced. 

Over breeding tortoises in my opinion just can't happen. They are too perfectly adapted at selecting the right sperm to fertilize. The sperm that isn't suited for fertilization are either absorbed by the body, or flushed out of their system. If you were over breeding your tortoises then you would have a lot of sick, or dead ones just from the stress alone. 

-Matt


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## dmmj (Jan 26, 2011)

so multiple breeding does not affect tortoises like say dogs and cat breeding does?


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## kbaker (Jan 26, 2011)

GBtortoises said:


> My thought on it: I think most split scutes can be attributed to low incubation humidity and gas build up in the nest site. Essentially birth "deformities" if you want to consider them as that. I have wild caught adult tortoises with and without split scutes and adult captive born tortoises with and without split scutes. Some of those adults with split scutes have never produced an offspring with split scutes and some of those adults without split scutes have produced offspring with split scutes. I think incubation temperatures, humidity and air exchange in the egg chamber during incubation play a part in a tortoise being born with split scutes. I have never seen one of my adult females, of any species, purposely choose a dry nest site. In fact, rain and warm tempatures are usually what triggers them to nest when and where they do when outdoors. Pretty much every nest that I have dug up has some degree of moisture in it. In most cases that moisture can usually be felt by touch. There is also almost always, at least 90% of the time, an air pocket above the eggs in an outdoor nest which allows for gas exchange and condensation collection. In rare cases I have had tortoises lay in a somewhat dry nest site only because there was not a more suitable spot for them at the time and the eggs had to be deposited. When I've had tortoises nest indoors the conditions are really not ideal. Their choice of nest site has been narrowed down to one spot for them. Sometimes not as deep as they'd like it and the soil, even though compacted, does not hold as true to form as that in an area outdoors that has usually been undisturbed and very well compacted naturally. Indoors they tend not to build the same nest cavity as they would outdoors. Whether the eggs are laid outdoors or indoors they all end up in an incubator. I used to have a lot more tortoises born with split scutes before I raised the humidity from about 60% up to nearly 80% that I strive for now. I still incubate at high temperatures to produce predominately female offspring (88-90 degrees) but between raising the humidity within the incubator and opening it twice daily for about 5 minutes at a time to allow for adequate air exchange, I very rarely ever have any tortoises born with split scutes anymore. So if it were genetic it would happen in spite of all of the above that I do.



I am going to have to go with this one. I think the wording might be off...as in not 'too low', but in the 'correct range'. I hatch Sulcatas and for the first two years I kept the humidity (gage says 98% all the time) and temps about 89F. I tried lowering the temps, but I still had a few with extra scutes. Right now the temp is at 87F and the humidity is at 76%. The last clutch was perfect. I am going to keep everything the same for the next two clutches and see what happens.

And one more thing, I have never used a tight fitting container for my Sulcata eggs. There has always been a good air exchange and of course, I can never keep my nose out of the incubator.



matt41gb said:


> I really don't truly believe that it's genetic. If splits scutes were in fact "genetic," they would have to arise from some mutation that's been passed down through the same bloodline.
> -Matt



I don't want to believe genetics either, but Terry K's hatchling pictures show a good arguement. He had two different hatchlings with the exact same (defect) scute pattern. Did I see correctly, Terry K?:shy:


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## Tom (Jan 26, 2011)

I don't have a lot of breeding experience, but I do listen to those who do. I have tow factors to add to the discussion.
1. This is not a "black or white" issue. Its very much a grey area. You can't say at 88.2 degrees, you will get exactly 72% split scutes. Warmer temps, and possibly lower humidity, simply increase the likelihood of split scutes. Those who breed a lot have told me that some adults DO tend to throw more split scuted babies than others of the same species, regardless of incubation conditions and temps.

2. We received a very technical presentation with lots of pics at the TTPG Conference this year. He explained that there are 12 "stages" of embryonic development and it is during just one of these stages the the sex is determined. If I remember correctly the scutes form during another stage. Temperature fluctuations only matter when they hit at a certain time in one of these developmental stages.


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## cdmay (Jan 27, 2011)

Split scutes might be genetic in some very rare cases but the two most common causes are temperature and humidity. Although I don't pretend to know how or what goes on in a developing egg that results in the deformities, I do know from my own experiences and those of others, who produce many hundreds of tortoise hatchlings each year, that the environment around the egg is the number one factor.
As was mentioned, wild tortoises are sometimes found with scute deformities and where a female places her clutch of eggs can determine whether or not hatchlings will emerge with supernumerary scutes.
For example, in some populations of gopher tortoises in disturbed areas of Florida there are a very high percentage of hatchlings found with extra scutes. This is because female gopher tortoises typically nest right at the apron of their burrows. In some cases this is right out in the hot sun and so the eggs incubate 'hot' and probably dry too. One researcher found that in certain areas an unusually high number of hatchlings with supernumerary scutes appeared each year due to a lack of any shade at the nest sites.

Although there have been some recent postings on this forum where captive breeders attribute their many hatchlings with deformed shells to genetics, the evidence is against them. If it were genetic then there would be a predictable number of hatchlings produced from each breeding--or within a given number of hatchlings--produced from the same adult(s). In addition, if the deformities were caused by a genetic control they would be uniform. Instead these breeders are producing many differing forms of anomalous scutes---hatchlings with a single extra vertebral scute, hatchlings with numerous extra scutes around the carapace, some with 'zipper' or ladderback scutes, others with only the odd split scute here and there and so on. They are random deformities caused during the incubation process and not genetic. 
In one captive breeding group of red-foot tortoises there have been supernumerary scute hatchlings produced from animals of the 'northern' type (including Surinam and Colombia) as well as the 'cherry-head' form. Unless the breeder is using the same dominant gene carrying male to breed all of his females (of differing races), the odds against the condition being genetic are astronomical.

Someone asked how it is that if conditions during the incubation process would produce one hatchling with extra scutes, then how is it that all of the hatchlings within that clutch don't possess them. Good question. 
It might be that there are hot spots within the incubator and actually this is pretty common. 
But then it could be similar to the condition that exists in human females who become pregnant later in life. In women over 40 years old the potential for producing a baby with Down Syndrome or twins is greatly increased but that doesn't mean that ALL women over 40 will give birth to DS children or twins. It just means that statistically, the odds are much greater. The same goes for incorrect incubation conditions and turtle/tortoise eggs--the potential for individual hatchlings to emerge with shell deformities increases with humidity that is too low and or temperatures that are too hot.


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## Madkins007 (Jan 27, 2011)

Carl-

I appreciated your comments- they were great! The thing that most caught my eye was the comment about the variation in an incubator. From what I have seen published, incubators for reptile and bird eggs all seem to struggle with even temps, and it appears that one of the reasons for cost differences between them is how well they can equalize that.

It reminded me of a cooking show I was watching that was talking about how important it was to rotate your cookies during baking because of the hot and cool spots in every oven. It is so easy to think of an oven, a microwave, an incubator, etc. as being perfectly evenly heated throughout- even when our experience with trying to heat a bedroom or something so clearly shows this is not the case.

I did not post on this or the other thread you mention since I have zip experience in it, but the research I have done certainly agrees with you. There IS a genetic component- a fairly predictable number of off-spring from an affected parent will produce certain consistent mutations- an additional central scute in the same place, for example. If I remember correctly, you had a Cherry-head that sometimes produced offspring with a nuchal scute. The key issue is that it will be consistent.

More random mutations are probably due to temps, humidity, or in some cases, problems with the ova or sperm (very young or old parent, dietary deficiencies, poorly developed glands*, etc.). A concern I have seen in the research is that the temps and humidity issues cause problems throughout the incubation period. If they happen at THIS point, it is split scutes, but if they happen at THIS point, it could be poorly developed organs, or other mutations and defects. If we see the split or extra scutes, there could easily be other anomalies, mutations, defects, or problems 'under the hood'.


*- One really interesting bit of research I have been working on is the effect of UV light on very young animals and their parietal or other 'deep brain' glands. In many species, it seems that adequate (several relatively small exposures over time) UV lighting helps stimulate these glands during their growth phase just after birth or hatching, which in turn help regulate sleep, activity levels, seasonal behaviors, and even reproduction. Just another benefit of natural light very early in life!


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## travisgn (Jan 27, 2011)

I'm gonna C+P what I just put in another threat, as well as add some additional info:

This is what I said over there in response to the idea that if split scutes were genetic it would be more predictable, or that there would be a predictable percentage, etc:

A new mutation is still genetic, even if it is completely unique. There are common genetic diseases in humans that research has shown are actually new mutations more often than inherited mutations. One example is muscular dystrophy - it results from one of many possible mutations along a relatively long segment of DNA that is prone to mutation. Certain segments of DNA are more prone to mutation for various reasons. The point is, it is very difficult to pin down an expected percentage for something of that nature. It can be done in humans (thanks to massive research into our genes, along with the whole sub-field of population genetics in play), but there isn't, and probably never will be, the research into tortoises that would be necessary. 

I wish to add:

I disagree that a genetic factor would lead to split scute patterns that are similar. This makes me think of polydactyly (extra fingers) in humans and other species. It is always genetic, yet it manifests MANY different ways. Why? Because there isn't one gene that codes for: "5 normal fingers" and one that codes for: "5 fingers plus 1 extra next to the pinky." Genes are much more broad than that, they affect entire populations of cells that contain an active form of that particular gene. Your hand develops as one flat, round blob until it differentiates into fingers. The faulty gene would be active in many, many cells in the hand at that point, but the error would manifest differently based on essentially just random chance.

I have no experience with hatching tortoise eggs, and as such I have absolutely no comment about whether split scutes are caused by environmental conditions. I would guess that they easily could be. I mainly wish to dispel some apparent misconceptions about genetics. There seems to me to be no definitive way to exclude genetics from the split scute equation, and it almost certainly plays a role at least some of the time.


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## cdmay (Jan 28, 2011)

travisgn said:


> I'm gonna C+P what I just put in another threat, as well as add some additional info:
> 
> A new mutation is still genetic, even if it is completely unique. There are common genetic diseases in humans that research has shown are actually new mutations more often than inherited mutations. One example is muscular dystrophy - it results from one of many possible mutations along a relatively long segment of DNA that is prone to mutation. Certain segments of DNA are more prone to mutation for various reasons. The point is, it is very difficult to pin down an expected percentage for something of that nature. It can be done in humans (thanks to massive research into our genes, along with the whole sub-field of population genetics in play), but there isn't, and probably never will be, the research into tortoises that would be necessary.
> 
> ...



Thanks Travisng, those are interesting things that I was not aware of.
I get your point about a new mutation being part of the individual's genetic makeup. But in cases where the mutation is caused by an environmental factor (such as the split scutes) does it follow that the new mutation can be passed on to the offspring of the individual that has the mutation?


In regards to split scutes and other deformities being caused by environmental factors I think I can add some further experiences...
In the late 1970s when a friend and I first started breeding tortoises we had no idea what temperatures to incubate our eggs at as there was nothing in print, that we had access to anyway, about hatching tortoise eggs. So we incubated at 88 to 90 degrees. The first year we produced 78 hatchling red-foot tortoises of which over 30 possessed split scutes while others hatched with deformed eyes and jaws. There were numerous eggs that failed to hatch and when opened those eggs were found to contain near term but deformed hatchlings. It was horrible but like I said, we had nothing to go on.
The next year we dropped the temperatures down to 85 to 87 degrees and out of the 50 something hatchlings none had deformed eyes but a couple still hatched with deformed jaws. There were a fair number of hatchlings with anomalous scutes though.
Finally we landed at the 82.5 to 84.5 temperature range that I still use today and the number of hatchlings with any visible deformities dropped to near zero. Over the years I have spoken to many other tortoise breeders from all over the world who report similar experiences. 
Many breeders have discovered that when they incubate their eggs at those higher temperatures, or in very dry conditions, the number of hatchlings produced with scute deformities increases dramatically. Thats just the way it is. 
In addition, incubating at higher (or lower) temperatures results in a skewed sex ratio of the hatchlings. This has been demonstrated in both in captive and wild populations. 
I guess there could be some genetic influence involved as you mentioned, but if so then a lot of tortoises have that predisposition.


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## Tom (Jan 28, 2011)

Thanks for sharing that Carl. We'd all be stumbling around in the dark if people like you didn't share experiences like that.

Great info.


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## Madkins007 (Jan 28, 2011)

travisgn said:


> I wish to add:
> 
> I disagree that a genetic factor would lead to split scute patterns that are similar. This makes me think of polydactyly (extra fingers) in humans and other species. It is always genetic, yet it manifests MANY different ways. Why? Because there isn't one gene that codes for: "5 normal fingers" and one that codes for: "5 fingers plus 1 extra next to the pinky." Genes are much more broad than that, they affect entire populations of cells that contain an active form of that particular gene. Your hand develops as one flat, round blob until it differentiates into fingers. The faulty gene would be active in many, many cells in the hand at that point, but the error would manifest differently based on essentially just random chance.
> 
> I have no experience with hatching tortoise eggs, and as such I have absolutely no comment about whether split scutes are caused by environmental conditions. I would guess that they easily could be. I mainly wish to dispel some apparent misconceptions about genetics. There seems to me to be no definitive way to exclude genetics from the split scute equation, and it almost certainly plays a role at least some of the time.



That is a valid point, but puts too much emphasis on what I meant by 'predictable'. To use polydactylism as an example- we can apply some basic rules and statistics to guess the outcome in the offspring- how many may manifest it, how many will carry it as a recessive gene, etc.

When it DOES manifest, we can predict certain things about how the errors will show up based on how the hand develops- blob, proto-hand, glove with thumb, fingers splitting off the glove in almost a spiral pattern. interrupt it for fused fingers, not stop it in time for a spare pinkie, etc. We would not expect to see a finger growing out of the 'plane', duplicate thumbs, toes growing instead of fingers, etc.

So I meant it in more the 'weather forecasting' sense- we can tell what should happen, within a range of possibilities- even if we can not state exactly what will be.

As to how this applies to tortoises- a different thread mentioned that many Aldaberans show a split in a specific scute as the result of a genetic flaw. Some torts have a higher incidence of offspring with splits than others, and the splits tend to be reasonably consistent. Carl May was able to get some Cherry-heads to show a nuchal scute, sometimes wide, sometimes skinny, sometimes not there at all- but it was always a nuchal scute.

As for environmental factors- there is an abstract from many years ago about how researchers could introduce rather consistent flaws by playing with incubation factors, so it is definitely an issue.

Great reply!


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## EricIvins (Jan 28, 2011)

I think too many poeple are looking at the genetics of split scute animals as simple recessive, or a mutation with a predictable outcome..........

Polygenic inheritance/mutations my friends.........They are hereditary, but aren't inheritable in any predictable way......With several different genes or possible influences controlling what's going on.......


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## cdmay (Jan 28, 2011)

EricIvins said:


> I think too many poeple are looking at the genetics of split scute animals as simple recessive, or a mutation with a predictable outcome..........
> 
> Polygenic inheritance/mutations my friends.........They are hereditary, but aren't inheritable in any predictable way......With several different genes or possible influences controlling what's going on.......



I might be guilty of that but then my experiences are from breeding reptiles (corn snakes, leopard geckos, etc.) that display simple and very predictable mutations. They were so predictable in fact that breeders could accurately determine what percentage of hatchlings from a given clutch of eggs would show each unique trait.


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## EricIvins (Jan 28, 2011)

cdmay said:


> EricIvins said:
> 
> 
> > I think too many poeple are looking at the genetics of split scute animals as simple recessive, or a mutation with a predictable outcome..........
> ...



Blood Red and Zigzag Corns come to mind then.........Even Piebald Ball Pythons......

Similair but different - At least with those traits above, they can be somewhat predictable in the sense that each Egg has a certain percentage of producing that mutation - However, you can NOT predict the outcome of how the trait manifests itself ( Low white, medium white, high white pieds, etc.... )

Polygenics may have one gene controlling different things, or those genes may be influenced by environmental or mechanical factors, among many other possibilities - Which would explain why every split scute/extra scute animal is different.......


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## moswen (Jan 31, 2011)

oh man, i'm so sorry everyone i had no idea this thread was giong to get so much long-posted traffic! my internet card is down and my tiny little cell phone screen is giving me an eye-ache, i've read several though and you guys have some great insight and some _really_ great experience on the subject! it makes sense about the individual air pockets and therefore differentiating temps and humidities in each egg... i really have not read that and had not thought about it either! 

that's why i love this forum, i can search and search all day and come up with the same 3 websites, and 10 people on this forum have more and better information than that! you all are great, i look forward to the time that i can read this all on a real computer screen lol!


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## travisgn (Jan 31, 2011)

> That is a valid point, but puts too much emphasis on what I meant by 'predictable'. To use polydactylism as an example- we can apply some basic rules and statistics to guess the outcome in the offspring- how many may manifest it, how many will carry it as a recessive gene, etc.



To some degree, perhaps. Polydactyly can be caused by recessive OR dominant inheritance, or by a new mutation. So it is very hard to determine possible outcomes, especially when you don't know the parental genes, which we usually don't, just like in tortoises. Throw in variable expressivity and incomplete penetrance of genes and guessing outcomes even in humans becomes extremely difficult, and seemingly impossible with a limited understanding of tortoise genomes.



> When it DOES manifest, we can predict certain things about how the errors will show up based on how the hand develops- blob, proto-hand, glove with thumb, fingers splitting off the glove in almost a spiral pattern. interrupt it for fused fingers, not stop it in time for a spare pinkie, etc. We would not expect to see a finger growing out of the 'plane', duplicate thumbs, toes growing instead of fingers, etc.



The amount of variation in polydactyly is, I think, roughly equivalent to what we see in scute malformation. You're right in part, you are going to see some variation on the expected form of a hand, but not toes or noses sticking out, but the same is true of torts. They simply have scutes that are the wrong shape or size, and in the wrong quantities. Polydactyly involves having fingers of the wrong shape or size, and in the wrong quantities. And as with scutes, almost anything within those limiting factors is possible: extra thumb, extra pinky, extra middle finger, digits with and without bones or nails, etc.

While tortoises with a single extra scute in a particular place having offspring with the exact same single extra scute in the exact same place seems to be obviously genetic, that doesn't make other scute malformations any less likely to be genetic, though it seems likely that we would be dealing with an entirely different mutation or set of mutations.



> Thanks Travisng, those are interesting things that I was not aware of.
> I get your point about a new mutation being part of the individual's genetic makeup. But in cases where the mutation is caused by an environmental factor (such as the split scutes) does it follow that the new mutation can be passed on to the offspring of the individual that has the mutation?



Referring to genetic "mutations" and environmental "mutations" does muddy the water a bit. I prefer to only use mutation for a genetic condition, just to avoid confusion. Anyway, a physical defect that is caused by environmental factors during embryonic development would not be passed along to offspring.


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