tortoisetrustforum.org

Yes. There is variation.

There is also (considerable) variation in size, colour, markings in species such as T. graeca graeca - to the extent you can pretty accurately say exactly where they came from, down to a few Km in some cases..

Andy

That in itself is interesting because their genotypes must be near enough identical.

Well, sadly, until I can get a bottomless bucket of funding for a research project of my choice and the freedom to roam around in any country I choose, I'm going to have to make do with reading about it (even if some of the papers are dubious - peer review, eh? ).

Yes, it is very interesting. It is also very consistently the case... across a lot of species, for example, people who know US Desert tortoises well (Gopherus) will tell you the same thing. You can identify examples from one area or another... in Spain, Marcos has mentioned how the T. g. graeca we have near us (Almeria) can be differentiated from those in his area (Murcia). They are supposed to be the same "subspecies"! I often say this: if they were Garter Snakes they'd all be different subspecies!

I found the same thing in Morocco. Incredible differences.

Andy

The pressure that the environment can put upon these torts is quite incredible when you think about it. Of course that is the way that genetic changes are forced over a long period of time - we're getting a window into evolution and for that I feel quite priviledged.

So, back to humidity and shell development. Where did the idea of a connection between them come from? I really can't see (no matter how I dress it up) that there can be any connection between humidity and smooth shell development. If that were the case, surely the torts would be under some osmotic pressure - and osmosis works both ways of course. I would imagine then that more damage would be done loosing water.

I can understand the importance of RH (or water saturation) to respiration and (for mammals) heat loss. How does this affect torts? Presumably they just move to the shade or a cooler area when they get too hot but does RH come into the equation anywhere?

Quite. The question would be: how can external ambient humidity affect bone growth?

Good question indeed.

Here is something very, very interesting and additional food for thought. Yesterday (Sat) we visited a local family who have tortoises in their garden. These tortoises just eat what grows there. The neighbour also had tortoises, and then gave them to the family we visited yesterday. Both of these gardens are in the natural habitat. Both get normal, full sun and natural UVB levels, etc. Identical climate. Identical plants. Identical soil. One single difference. The neighbour fed her tortoises on kitchen scraps evety day, mostly lettuce, instead of letting them forage for themselves.




As far as I can determine, that was the only variable in his situation. The tortoises fed on lettuce have visible MBD and are clearly 'pyramided'.

Interesting, I think, and quite illuminating.

Andy

Umm ... real food for thought, as you say.

Lets re-cap a bit then. We've all but eliminated ambient humidity as a cause of pyramiding. Humidity will play a role in other functions such as respiration and water loss. Hydration is clearly important for efficient functioning of the urinary system and is necessary for electrolyte balance, cellular processes and so on, much as it is in all other animals.

That brings us onto diet and mineral uptake.

Where a wild tortoise has free range and a choice of a number of different plants to eat, do they show a preference for a particular plant/group of plants?

It goes without saying really that calcium intake is vital to bone (and shell) growth. Where there is a lack of calcium the internal organs take preference and calcium will be leached from the bones. This results in a porous structure of bones with a weakened matrix. I know that in humans, bone formation is dynamic, with constant breaking down and re-formation. If this is the case in torts as well, then ensuring adequate calcium intake for youngsters and gravid females isn't enough - it has to be sufficient for life. In the case of torts with MBD, is what we're seeing then a collapse of the structures supporting the shell, which can vary from being localised to the base of each scute in the least severe cases, to complete collapse of the carapace in the worst?

Presumably in your example, the lettuce wasn't supplemented with any foodstuff with a higher calcium content?

As far as I can tell (I am relying on what I am told) the tortoises would have munched on some natural vegetation, but basically, the vast majority of the intake was lettuce, tomato, etc. So this would have resulted in a relatively low calcium diet during the most critical growth period, from hatching onwards. Certainly UVB, temperature, etc., would have been absolutely fine. They had the same access to drinking water as the wild ones beyond the fence. It is not exceptionally severe deformity by any means (no high protein foods were given), but I think it fair to say this is the result of over-feeding on a low (but not critically low) calcium-content diet.

I'd really like to get an x-ray of these...

Andy

Is this what causes pyramiding, then - a collapse of the bone at the edges of each scute, leaving the scutes apparently raised?
Or is pyramiding abnormal growth in the wrong direction as it were (upwards rather than outwards)? If the latter, why would that happen?

Are there any postmortem cross section pictures avalable of a pyramided shell? I've seen some elsewhere (on one of Andy's DVDs) of a collapsed spine and carapace, but not of pyramiding as such.

Just trying to further understand the phenomenon.

Stuart

Another question then (sorry!)....from a human angle again - high protein intake has a detrimental effect on calcium retention. This is more marked in the case of animal protein though still occurs with plant proteins. It's my understanding that this is caused by an increase in filtration rate and an inhibition of calcium re-absoption through renal tubules. Do you think this happens with torts too? If so, those poor animals that were fed a diet of dog food were really dealt a double whammy - they were doomed from the start

The un-absorbed calcium would presumably pass through the kidneys and into the bladder for excretion. A bizzare situation then arises where the animal suffers from lack of calcium but is actually excreting precisely what it needs.

Is it possible to give too much calcium?

Just take any dead tortoise with this condition, do a section, and you have your answer.

Stuart, yes, the photos I used there do in fact depict the condition internally.




That is a totally healthy, well formed tortoise.

Andy