Following some initial analyses of the imported Horsfield's tortoises an interesting pattern has emerged.  In an earlier post I reported some preliminary results: nitrogen signature (d15N) varies significantly between individual tortoises and the carbon signature (d13C) of growth of a medium age is significantly higher than that of new growth.  When I took the samples I also noted whether I thought the specimens had lumpy or smooth shells: a lumpy, or 'pyramided' shell is often a sign of a captive tortoise. 
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Figure 1. Changes in carbon and nitrogen signature for individual tortoises with lumpy (blue), smooth (red) and unclassified (yellow) carapaces.

When pooled, this data sorts the tortoises into two distinct groups, suggesting that they come from different populations (figure 1).  My guess would be that this reflects a split between wild-caught and ranched individuals; though this is speculation it does seem to warrant further investigation... 
3/13/2012 01:29:40

I have seen comments on some tortoise forums that pyramiding is not necassarly a sign of being captive breed but linked to humidity. Do you know of any active research on this subject?

Thanks

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