Sampling the carapace took a while – but at least it was a relatively clean job.  A week ago every time I closed my eyes I saw an image of a tortoise carapace – quite pretty but after a while somewhat annoying.  Now I close my eyes to see the internal anatomy of a tortoise, and am followed around by the accompanying smell.  Needless to say I preferred the former…

And yet I always did like dissections however morbid they may be. 

Tortoises present a problem – how do you get into them?  Rather foolishly I initially tried using a scalpel – I have no idea why I thought this was in any way logical but I’m going to use the excuse of being tired.  A good night’s sleep and three broken blades later I realised my mistake and went out to buy a hacksaw.  This was far more productive, though drew some strange looks from others in the lab.  Mind you it still took a while to actually get the carapace off – these are incredibly tough little beasts!  The experience has definitely renewed my respect for lions, having watched them crack open tortoises with their teeth when I was in Africa several years ago…

Anyway – why the dissections?  Well, different tissues turnover at different rates: the keratin of the carapace once formed does not change, so it reflects the diet at the time of growth.  Blood, liver and muscle have varying rates of turnover, with blood reflecting the shortest time period.  As far as I know turnover rates have not been calculated for tortoises, but those for the pondslider, Trachemys scripta, are surprisingly slow with a Nitrogen turnover rate of 155 days for whole blood (Seminoff et al, 2007).  Although all the evidence points to the pattern of scute growth shown in my previous post, there has been little work on how tortoise scutes grow.  It is therefore worth checking that the isotopic values of soft tissues correspond best with the values for what I believe to be the most recent growth.  

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