UV through carapace or not

[Anyfoot]

Hi All

Does the shell/carapace absorb UV rays? I was always under the impression it did, not as well as the skin does, but to a certain degree. I was led to believe that the shells are made up of the same stuff as fingernails and hair, known as Keratin. Hair changes colour in the sun, and talking to some of our tort breeders on here, torts shell change colour in the sun. Is the colour changed linked to UV absorption? I understand that torts will sprawl out with head and limbs far out to absorb heat and UV. But I always assumed there was an element absorbed through the shell too. Is there any concrete scientific evidence that eliminates the fact that shells do not absorb UV. Tried to research this on the net, but it seems to be a topic of opinions not fact.

Something that I have often thought about, is when a tort has a mud bath in the wild and gets caked in mud. Surely the mud stops UV absorption, and I'm guessing the mud is caked on until the next rainfall. Firstly, does this happen and secondly, if so where does the tort get its vitamin D from during this period.

Can anyone enlighten me on this subject please

Thank you all.

Craig

 

[Anyfoot]

Hi Craig. Couple of things. First, the shell probably does absorb UVB because as you point out, other keratin structures such as hair do. Other evidence is the faded shells common to older, outdoor tortoises. Also, uv doesn't reflect much.
This is different than the biosynthesis of vitamin D, which is what tortoise people are always worrying about. This is a photochemical reaction that takes place in the skin.

Here's a general reference on the process if you want more info.

[Vitamin D: biosynthesis, metabolism and mechanism of action at the cellular level].
Review article
Berdal A. J Biol Buccale. 1992.
Show full citation
Abstract
The term vitamin D includes various chemical species. Vitamin D3 a true endogenous or alimentary prohormone is converted into its main metabolite, calcitriol, by successive hydroxylations in the liver in position 25 and in the kidney in position 1, the production of which is controlled by several factors including parathyroid hormone, blood calcium and phosphorus or insulin as well as by the metabolites of the hormone itself. It controls the synthesis of numerous peptides by acting on gene expression. Indeed, several structural proteins are involved including procollagen alpha 1l, core protein of proteoglycans, diverse regulatory peptides such as protooncogene c-myc and growth factors, "Tumor Necrosis Factor or TNF" and "Nerve Growth Factor or NGF" or hormones such as parathyroid hormone, and finally constitutive proteins of the mineralized tissues such as osteonectin, osteocalcin, osteopontin and calbindins. Therefore, it modulates very different cellular processes. It acts via a nuclear receptor the structure and function of which have been investigated by genetic engineering (cloning of genes encoding for the receptor and hormono-dependent peptides, transfection assays, directed mutagenesis). Actual studies investigate its role in the formation of the complex for transcription initiation near ADN sites, the "Vitamin D Responsive Element or VDRE", located upstream vitamin D-responsive genes and approximately RNA polymerase II. The receptor, which is present in many cell types at various concentrations, would determine spatial and temporal patterns of calcitriol action during development in conjunction with chromatin factors.

Thanks zeno. I was going to tag you in but, thankfully you found my thread. Very helpful. I have another question I've found contradicting when researching on the net. Do animals get any vitamin A from the UVA spectrum. Thanks again for your help.

 

[Tidgy's Dad]

UVB does fade colours and your torts' shells by photodegredation,where the chemical bonds within the colour retaining chromophores are broken down so that the colour seems to fade.
UVB is reflected, so bounces about outside, ensuring you and your tortoise receive some quantity of UVB even in the shade. Different materials reflect different percentages of the UVB, snow more than 70%, the sea 20 to 30% and sand or dry soil 10 to 15%, for example. Shade reduces UVB exposure by about 50%. UV amounts increase by 4% every 300m above sea level.
UVA is absorbed by the skin, but causes sunburn and the destruction of vitamin A in the skin. I'm not sure if it has any benefits in tortoises.

 

[Anyfoot]

UVB does fade colours and your torts' shells by photodegredation,where the chemical bonds within the colour retaining chromophores are broken down so that the colour seems to fade.
UVB is reflected, so bounces about outside, ensuring you and your tortoise receive some quantity of UVB even in the shade. Different materials reflect different percentages of the UVB, snow more than 70%, the sea 20 to 30% and sand or dry soil 10 to 15%, for example. Shade reduces UVB exposure by about 50%. UV amounts increase by 4% every 300m above sea level.
UVA is absorbed by the skin, but causes sunburn and the destruction of vitamin A in the skin. I'm not sure if it has any benefits in tortoises.

Thanks for clearing that up for me. Yes uv dies reflect. I've fished most part of the day facing the sun before but yet got a red neck. As your new avator come with an encyclopedia or what. Thanks mate.

 

[Tidgy's Dad]

Thanks for clearing that up for me. Yes uv dies reflect. I've fished most part of the day facing the sun before but yet got a red neck. As your new avator come with an encyclopedia or what. Thanks mate.

It's zenoandthetortoise's old avatar.
I begged so much he took pity and gave it to me.
Perhaps it comes with some of his knowledge.

 

[Anyfoot]

It's zenoandthetortoise's old avatar.
I begged so much he took pity and gave it to me.
Perhaps it comes with some of his knowledge.

It's zenoandthetortoise's old avatar.
I begged so much he took pity and gave it to me.
Perhaps it comes with some of his knowledge.

I believe non ferrous metals deflect uv the best. Aluminium/copper etc.

 

[Tidgy's Dad]

I believe non ferrous metals deflect uv the best. Aluminium/copper etc.

Sounds about right to me, hence reflectors in terrariums, but I'm not sure.
That bit didn't come with the avatar it seems.

 

[Anyfoot]

Sounds about right to me, hence reflectors in terrariums, but I'm not sure.
That bit didn't come with the avatar it seems.

Zenoandthetortoise is street wise I see. Dont give everything away all at once. Lol.

 

[Anyfoot]

Sorry, I wasn't clear. UV doesn't reflect much off of biological surfaces is the point I was trying to make.
Did you mean my new avatar or Tiggys dad's new avatar?

I meant tidgys avatar. He has yours and it seems to have given him the knowledge too. Lol.

 

[Tidgy's Dad]

Sorry, I wasn't clear. UV doesn't reflect much off of biological surfaces is the point I was trying to make.
Did you mean my new avatar or Tiggys dad's new avatar?

Tiggy?
Tiggy?
Anyway, I'm Adam.