tortoisetrustforum.org

Nothing at all to do with water balance, Marcos.

I'll show you exactly what is happening when I see you next.

I want to make sure I have the best possible data before I finally publish these results.

Andy

Aghhhh your answer involves patience on my part

I just hope to be able to understand your explanations My knowledge on physiology is very basic

Thanks a lot!!!

Apologies if I'm butting in but this is a fascinating debate and a subject in which I am particularly interested.

Unfortunately the research mentioned above has several problems in my opinion. The obvious are that it is too small (50 individuals) and too short a duration (5 months). There are several variables which will confound the results. If one variable is being tested (eg humidity) then that should be the only condition varied and there should be more (and closer) intervals - maybe vary the RH by 5% at a time, say groups of torts in 10-15% RH, 15-20% RH, and so on. To conduct a study where there is another variable, in this case dietary protein, means that firm conclusions cannot be made as to which condition is causing the observed changes.

Several questions come to my mind when I'm reading the paper...

1. Can we be certain that the environmental test conditions play no part in the observations?
2. Water and a calcium source were available for the torts to take freely but without observing them constantly, there would be absolutely no way that the researchers could be sure that intake was consistent between individuals.
3. They studied G. sulcata but I think as they were testing pyramiding per se, they should have looked at different species.
4. Just because eggs were taken from less pyramided parents at the farm, does not necessarily mean that there is no genetic component - ie. it could be a recessive condition.

There's little doubt in my mind that this type of research really needs to be done on tortoises in the wild to be credible. Where there are differences occurring naturally between individuals - G. elegans being a perfect example - researchers could make long-term observations of humidity and diet and any other possible factors by recording what happens naturally rather than creating the conditions artificially.

Great debate though.

That is, of course, exactly what we are doing.

I'd also highlight another very serious flaw in the study. There was no radiography whatever and hence no data at all on bone density and development. It was entirely based on external observations and some blood work.

Andy

...and unfortunately, the 'hump' measurements could only be semi-quantitative at best.

There's no quick way to do this type of research but at least taking measurements and observations in wild populations interferes least with the animals themselves. To do a long-term trial on the necessary experimental numbers, in a laboratory situation does not sit well with me - especially where the aim is to induce non-favourable growth at obviuos detrement to the animals.

The other problem of course is that whilst it would be great to get a definitive answer to the subject of pyramidal growth, I can't see it being straightforward - it's likely to be multi-factoral (?)

It is certainly is multifactorial inso far as causation, Sue. It can be helpful to look specifically at why this is very, very rarely encountered in nature (and then, in my personal experience, only following human influence - agricultural interference with the diet! ).

1) Wild tortoises receive excellent UVB, UVA and visible spectrum exposure. Even the best artificial lamps struggle to get close in all parameters, most do not even come close.
2) They achieve skin temperatures typically in the 36-38 C range, with core temperatures around 32-34. Combined with the sunlight they receive, this adds up to truly optimal conditions for generating D3. In captivity, these figures are rarely seen.
3) The diet is unbelievably rich in calcium. Calcium is everywhere in these habitats.
4) Food intake is highly cyclic, with long 'rest' periods due to hibernation, estivation, retreat from other adverse conditions, etc. It is not a constant, daily thing.
5) The 'food value' is quite low., i.e., low in protein (wet value), very high in fibre, quite high in water content too during peak growth phases. The combination of this, plus the cyclic feeding, results in relatively slow growth.

The net result of all of the above is that bone development is simply superb. Very high density, very even.

This should be contrasted with the typically poor bone quality achieved in most captive situations......

Andy

Interesting stuff.

I'm going to quote G. elegans as an example again. These torts I believe are the only example where pyramidal growth is observed in wild populations and this occurs without any associated pathology. I've seen photos of these torts in the wild (at least that's what I'm told!) and some examples are really quite pronounced. From reading around it seems that in certain areas of their normal habitat they can be literally overwhelmed with food - sometimes from abandoned bean fields and other nutrient-rich plants.

My own feeling is that normal food shortages, coupled with poor food quality and having to range a long way to find food, all contribute to normal smooth growth. Maybe many captive torts don't get sufficient exercise?

What do you think might be happening in the case of G. elegans?

That's my point. I try to imitate nature as much as I can, and I am getting good results with graecas (quite easy here in Spain) but STILL I would love to understand the whole process, and a explanation to the good 'external results' other people achive using very different methods from mine, even if they are harmful, I don't trust them and I am not going to try them...ever. I find it interesting.

It's genetic, at least in its normal form. What I mean by that is that there is a normal amount of growth that looks superficially like the 'pyramiding' seen in poorly raised captive specimens. Like this:



That is normal. The growth there is typical. Also, bone density is normal (can be proven by x-rays and by examining shells of museum specimens, etc.). This is an inherited trait and passed on the young. One can speculate on the advantage it confers - It is likely to be either thermal, or cryptic, or a balance of both.

Then... yes, you can indeed get Geochelone elegans with nutritionally induced MBD. Here's one:



It is very interesting indeed that the 'other' tortoise where the same, genetically directed growth occurs is Psammobates tentorius:



(P. t. veroxii shown here). It also shares the 'star' pattern, which I tend to feel points in the direction of this type of growth being advantageous when combined with that class of marking. They are certainly incredibly hard to find in their natural habitat!

It really must be stressed, though, that the 'pyramiding' seen in healthy Stars and Tent tortoises has NO RELATION WHATEVER to the nutritionally induced MBD as seen in poorly grown Testudo, etc. That is easy to demonstrate by simply taking some x-rays or bone samples. One is a pathology. One is not. They are merely superficially similar in appearance, which has misled a lot of people.

Andy

Thanks Andy.

As you say, there must be some evolutionary advantage to this type of growth. I can appreciate that the star patterns will elongate slightly and they certainly can be extremely difficult to find in dry grass, I've seen this with mine - they are very well camoflaged.

I wonder then if there's variation between the torts found in Sri Lanka and the southern part of India to those found in the north and Pakistan?