# Female tortoises having a flexible plastron at adulthood



## turtlesteve (Sep 16, 2019)

So I've read in a few articles, both scientific and not, that female tortoises of some smaller species will develop a slightly flexible plastron when they start laying eggs. Some articles suggest this is adaptive, but without direct evidence, as it's also obvious that a gravid female will require more calcium. So, my question is, would you view this as a negative (i.e. it suggests calcium deficiency due to making eggs) or a positive (it's an intentional adaptation to prevent the female from becoming egg bound)? 

Steve


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## Tom (Sep 16, 2019)

Never heard of this one. New info for me.


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## Millerlite (Sep 16, 2019)

Do you have any links to these articles? 

Kyle


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## turtlesteve (Sep 16, 2019)

Here's one example from http://www.reptilesmagazine.com/Reptile-Magazines/Reptiles-Magazine/July-2009/Golden-Greek-Tortoise/

"The plastron joint between their rear and central plastron plate also softens in mature females, transforming it into a slightly flexible hinge. This allows the rear plastron to open wider during egg laying."

I'll have to dig to find the other references, it's been a little while since I read them and I didn't save the articles.


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## Millerlite (Sep 16, 2019)

turtlesteve said:


> Here's one example from http://www.reptilesmagazine.com/Reptile-Magazines/Reptiles-Magazine/July-2009/Golden-Greek-Tortoise/
> 
> "The plastron joint between their rear and central plastron plate also softens in mature females, transforming it into a slightly flexible hinge. This allows the rear plastron to open wider during egg laying."
> 
> I'll have to dig to find the other references, it's been a little while since I read them and I didn't save the articles.


Hmm. I was wondering if there were any scientific research articles on this or if it's just all speculation. I would imagine no one has really studied this specifically so it's really hard to say if its actual fact and if so what species show this and does this trait link to something else other than just laying ... I'll look around some of the archives I have access too see if anyone studied this, sad part is not much actual studies have been done in tortoises and turtles and most that have been done are select species and mostly sea turtles.


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## turtlesteve (Sep 16, 2019)

Also noted here and suggested to be adaptive:
https://tortoise.org/archives/speckledTort.pdf
https://www.eaza.net/assets/Uploads...se-EAZA-Best-Practice-Guidelines-Approved.pdf


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## turtlesteve (Sep 16, 2019)

Millerlite said:


> Hmm. I was wondering if there were any scientific research articles on this or if it's just all speculation. I would imagine no one has really studied this specifically so it's really hard to say if its actual fact and if so what species show this and does this trait link to something else other than just laying ... I'll look around some of the archives I have access too see if anyone studied this, sad part is not much actual studies have been done in tortoises and turtles and most that have been done are select species and mostly sea turtles.



I know I've seen it in a published scientific article somewhere too, but it was not any less speculative than the above. But on the flip side, I've also seen articles suggesting a soft plastron is symptomatic of calcium deficiency. It would be nice to understand so I know how to treat / react to this when I observe it (not that extra calcium supplementation would necessarily cause harm).

Steve


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## zovick (Sep 22, 2019)

turtlesteve said:


> I know I've seen it in a published scientific article somewhere too, but it was not any less speculative than the above. But on the flip side, I've also seen articles suggesting a soft plastron is symptomatic of calcium deficiency. It would be nice to understand so I know how to treat / react to this when I observe it (not that extra calcium supplementation would necessarily cause harm).
> 
> Steve



I believe the scientific article(s) to which you are referring were written about the Spider Tortoises (Pyxis). I don't have a reference for it, but years ago, there was at least one article stating that the rear lobe of the plastron on the females of this genus became flexible at the time eggs were laid to make it possible for the eggs to pass through the very narrow space between the carapace and plastron without breaking. It was not due to a calcium deficiency, but due to the same hormonal changes which brought about oviposition in the females.

I was keeping all four of the Pyxis species at that time and can remember actually seeing blood ooze out of the seams which had become flexible when the females were laying eggs. To me, this illustrated the point that hormones in the blood were causing the joints to become movable. The rest of the shells, both plastron and carapace, were totally solid. In a calcium deficient animal, one would expect that the entire shell would be affected, not just one portion of it.


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## turtlesteve (Sep 22, 2019)

zovick said:


> I believe the scientific article(s) to which you are referring were written about the Spider Tortoises (Pyxis). I don't have a reference for it, but years ago, there was at least one article stating that the rear lobe of the plastron on the females of this genus became flexible at the time eggs were laid to make it possible for the eggs to pass through the very narrow space between the carapace and plastron without breaking. It was not due to a calcium deficiency, but due to the same hormonal changes which brought about oviposition in the females.
> 
> I was keeping all four of the Pyxis species at that time and can remember actually seeing blood ooze out of the seams which had become flexible when the females were laying eggs. To me, this illustrated the point that hormones in the blood were causing the joints to become movable. The rest of the shells, both plastron and carapace, were totally solid. In a calcium deficient animal, one would expect that the entire shell would be affected, not just one portion of it.



Thanks - that's the kind of information I'm looking for. Do you by chance have the reference handy?


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## zovick (Sep 22, 2019)

turtlesteve said:


> Thanks - that's the kind of information I'm looking for. Do you by chance have the reference handy?



As I said in the second sentence of the post you quoted above, I don't have a reference right now, but if I find it, I'll post it. This was back in 1998-2002, so I am not overly confident I can find it now.


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## zovick (Sep 22, 2019)

turtlesteve said:


> Thanks - that's the kind of information I'm looking for. Do you by chance have the reference handy?



I didn't see anything about the females' plastra becoming more movable in the following paper, but you might find the information in one of the articles in the bibliography if you have the time to look them up. I don't, but if I stumble upon anything else, I will post it here.

Here is it is: http://www.chelonian.org/wp-content/uploads/file/CRM%206/24-Pearson.pdf


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## mark1 (Sep 22, 2019)

in dogs the hormone that causes ligaments to loosen is called relaxin ………..


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## ShirleyTX (Sep 30, 2019)

I've read in multiple articles that the small Egyptian tortoise also has a hinge that will be slightly moveable for egg laying, especially important since Egyptian eggs can be large in relation to the female's body size.


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## wccmog10 (Oct 1, 2019)

Several years ago I remember looking into what constrains egg size (we were looking at size of egg vs number of eggs). I remember an article about this subject- I’m pretty sure that this is the one I was thinking of- link is below. The part of interest starts at the bottom of page 1349 “Shell and pelvic kinesis”

https://www.researchgate.net/profil...in-the-smallest-tortoise-Homopus-signatus.pdf


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## mark1 (Oct 1, 2019)

it is an actual biological process...…. fish , birds and mammals all exhibit this ability enabled by the hormone relaxin , I would think tortoises and turtles are no different , I actually think folks who study such stuff feel the same ……


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## Tortoise MasterMan (Nov 25, 2019)

This is very interesting.


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