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.
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...