Leopard Tortoise

[EJ]

This is my last 4th generation Leopard tortoise. She's about 6 inches SCL. I believe the coloration is due to the environmental conditions under which she is kept... I hate the color. I'm hoping once she gets outside she will darken up and look normal...


This is a WC Leopard that I got from a confescation. Notice the new growth is coming in light. She is kept with the light tortoise...

[Mick.Ire]

Out of interest, what are the environmental conditions you keep them under? Would it not be better to try and maintain the WC's beautiful markings? Is it no UV?

[EJ]

That's what I'd prefer but my situation dictates how I keep my animals. I am working on adding UV to all the enclosures but it is expensive, time consuming and a logistical challenge.

I'm thinking that it is the constant high heat and possibly the lack of UV that is the cause. I am goig to give them more access to the outdoor lighting with the onset of spring.

Originally Posted by Mick.Ire

Out of interest, what are the environmental conditions you keep them under? Would it not be better to try and maintain the WC's beautiful markings? Is it no UV?

[Baoh]

In my experience, it is usually high heat which causes the high white and reduced pattern result. There may be those with genetic predispositions, too, but most of what I see on the market or as pets seems to be due to relatively high heat. I have seen high heat induce RF marbling, too. Either some where there was previously none or exacerbated in animals which have it naturally occurring.

I did some experiments regarding the "hot" coloration seen in reptiles (I worked mainly with leopard geckos and only a few chelonian embryos) incubated at higher than normal temperatures. I also did some electrophoretic work based on my hypothesis, which is that the tyrosinase enzyme function becomes impaired as temperature increases (which would be expected, really, when one thinks about the effect of thermal energy on protein structure) for the sake of possibly turning the work into a paper, but I basically stopped giving a care about the idea of the paper after I got my answer and never went all the way with that aspect of things.

I believe the instances of particular animals which seem to exhibit these effects more readily than peers may be due to tyrosinase isozyme variants that happen to have lower Tm values or something similar, and lose functionality at a lower thermal energy level than might otherwise be typical.

[EJ]

How did you rule out exposure or lack of exposure to UV?

To be honest... I didn't understand most of what you said.

Originally Posted by Baoh

In my experience, it is usually high heat which causes the high white and reduced pattern result. There may be those with genetic predispositions, too, but most of what I see on the market or as pets seems to be due to relatively high heat. I have seen high heat induce RF marbling, too. Either some where there was previously none or exacerbated in animals which have it naturally occurring.

I did some experiments regarding the "hot" coloration seen in reptiles (I worked mainly with leopard geckos and only a few chelonian embryos) incubated at higher than normal temperatures. I also did some electrophoretic work based on my hypothesis, which is that the tyrosinase enzyme function becomes impaired as temperature increases (which would be expected, really, when one thinks about the effect of thermal energy on protein structure) for the sake of possibly turning the work into a paper, but I basically stopped giving a care about the idea of the paper after I got my answer and never went all the way with that aspect of things.

I believe the instances of particular animals which seem to exhibit these effects more readily than peers may be due to tyrosinase isozyme variants that happen to have lower Tm values or something similar, and lose functionality at a lower thermal energy level than might otherwise be typical.

[Baoh]

Originally Posted by EJ

How did you rule out exposure or lack of exposure to UV?

To be honest... I didn't understand most of what you said.

I have raised animals with UV and without (but with supplemental D3) for the tortoise examples as well as witnessed the care parameters of others, many of whom did use MVB and FL light sources that were UVB emitting. UV did not seem to impact things substantially for the animals I have observed in my own care or in the care of others.

Conversely, sulcata growth indoors seems to, in my experience, be generally darker. Even with artificial UV sources and high heat. When I put such darker inside animals outside, they faded/lightened significantly. Of course, that could be a matter of the exact isozyme, but I cannot say for sure since I tested nothing to that effect.

To rephrase what I think you may not have followed in short from the previous post, I did some work to look at tyrosinase (melanin producing enzyme) functionality and found reptile tyrosinase from my admittedly limited samples to be negatively impacted by heat, including change in enzyme structure before reaching the upper end of what can be withstood by a living reptile. It would stand to reason that, above a certain threshold, it is perhaps due to this that some individual reptiles or types of reptiles seem to exhibit a disruption in melanin production with increased environmental heat. UV exposure was not a relevant factor in the experiments I performed. A followup prediction is that there are variations in the enzyme across species and individuals that amplify the potential for these types of observations in color aberrations in response to the environmental factor of heat. Naturally, exceptions abound and this is by no means a rule. Just a trend.

I suppose there was nothing short about that "in short", though.

[EJ]

That's ironic... In my experience indoor growth tends to be lighter. The two Leopards pictured are kept relatively cool with a high temperature of about 85F under the lamp.

New growth in Sulcata is usually darker until the keritin acquires calcium and gets sun bleached... if kept outdoors.

Isn't melanin production related to UV exposure and not heat.

(Thanks for the rephrase)

I'm curious... how did you measure the melanin producing enzyme?

Originally Posted by Baoh

I have raised animals with UV and without (but with supplemental D3) for the tortoise examples as well as witnessed the care parameters of others, many of whom did use MVB and FL light sources that were UVB emitting. UV did not seem to impact things substantially for the animals I have observed in my own care or in the care of others.

Conversely, sulcata growth indoors seems to, in my experience, be generally darker. Even with artificial UV sources and high heat. When I put such darker inside animals outside, they faded/lightened significantly. Of course, that could be a matter of the exact isozyme, but I cannot say for sure since I tested nothing to that effect.

To rephrase what I think you may not have followed in short from the previous post, I did some work to look at tyrosinase (melanin producing enzyme) functionality and found reptile tyrosinase from my admittedly limited samples to be negatively impacted by heat, including change in enzyme structure before reaching the upper end of what can be withstood by a living reptile. It would stand to reason that, above a certain threshold, it is perhaps due to this that some individual reptiles or types of reptiles seem to exhibit a disruption in melanin production with increased environmental heat. UV exposure was not a relevant factor in the experiments I performed. A followup prediction is that there are variations in the enzyme across species and individuals that amplify the potential for these types of observations in color aberrations in response to the environmental factor of heat. Naturally, exceptions abound and this is by no means a rule. Just a trend.

I suppose there was nothing short about that "in short", though.

[Baoh]

Originally Posted by EJ

That's ironic... In my experience indoor growth tends to be lighter. The two Leopards pictured are kept relatively cool with a high temperature of about 85F under the lamp.

New growth in Sulcata is usually darker until the keritin acquires calcium and gets sun bleached... if kept outdoors.

Isn't melanin production related to UV exposure and not heat.

(Thanks for the rephrase)

I'm curious... how did you measure the melanin producing enzyme?

To clarify, for leopards under higher heat indoors, with or without UV, they were higher white in my observations. For sulcatas kept indoors without access to sunlight, even with heat, they were darker in my observations.

I do not know if it is actually a bleaching effect in dark sulcatas placed outdoors that lighten, but I do observe them to lighten with prolonged exposure to sunlight regardless. I do agree that it probably is bleaching in those cases, as it goes for human hair, but I have not tested that.

Keratin has no significant calcium in it. Keratin-based tissue is typically unmineralized (including the beta-keratins we would be discussing in relation to chelonians). Calcium would have no reason for incorporation, as it would interfere with the toughness of the polymerized end product of hydrogen bonding that characterizes the strength of beta-keratin sheets. Anything extra added means something less of a stable construct. Pigment is a fair trade because the cost of including it is in exchange for an improvement in crypsis and thermoregulation potential. Calcium would yield what advantage in the resultant structure? Nothing readily apparent to me. It would be a double cost. 1) It would be at the expense of other systems that utilize calcium such as structurally (skeletal) or as an electrolyte (or in muscle contraction). 2) It would be at the expense of structural integrity of scales, scutes, beaks, and claws. Also, what would be the mechanism for the keratin to have calcium incorporated later? It is dead beyond the finest growth layer. There is not a transport mechanism such as microvascular network beyond that very thin growth margin. It relies on self-assembly and H-bond strength to render its tough nature. There would be nothing to move Ca from A to B at a point beyond initial assembly, so there is not a way for there to be a step that comes later unless it (the conduit) has not been revealed yet (and having looked at photomicrographs of scute structure some time ago, I did not see any).

Yes, melanin production can be partially in response to UV exposure, but it can also be expressed in ectotherms due to a lack of light or heat. Darkening makes for a more effective ability to absorb and retain thermal energy. Animals with a more rapid and transient response achieve a quicker effect via chromatophore (especially melanophore) shifts (more accurately, pigment translocation). Many lizards, for instance, show this effect when cold or otherwise distressed.

As a mammal, my hair has significant visible melanin regardless of exposure (and lightens with exposure). My skin's visible content increases in response to UV exposure. My colleague from Kenya's apparent level does not visibly shift like mine.

I measured the enzyme's functionality in terms of a few things. One was simply enzymatic kinetics work via substrate consumption/alteration rate over a time course with known starting levels of substrate and measurable end products (as well as some ITC binding work). I also looked at unfolding or melting events, as well as looked for hysteresis, via differential scanning calorimetric methods and dye-labeled fluorescence. Finally, I looked, via an electrophoretic method, at molecular weight compared to known markers and observed, post-purification and temperature cycling, what kind and percentage of degradation products (dimers, higher-order aggregates, and fragments) resulted. I may pick it up some day again, as it is sort of novel, but I am more of a product driven kind of guy, so my interest is more related to the products I develop, patents I might be awarded, and stuff like that. I do not have a definitive super-strong answer based on what I did. More of a body of evidence supporting a particular hypothetical hunch I had. To make it ready for publication in a highly reputable journal would take more resources than I am currently willing to devote, IMO. Without giving my work away, that should provide some measure of an answer to your question. I hope it did, although it may require some familiarity with these analytical techniques to glean the full value in/of the response.

[Mick.Ire]

Holy sh*t, I started reading this thread on my phone but quickly gave up. I'll wait until I get home on a bigger screen and dictionary lol.
Look forward to an interesting read though.

[Lisamn]

Baoh, can I ask what RF marbling is please (in simple terms)? Also, you mentioned that tortoises kept without UV suffered no ill effects (I'm paraphrasing here). Do you just mean terms of their markings and colouring, or do you include general health and well-being too?