The use of shell morphometrics for the management of the endangered malagasy radiated tortoise (Geochelone radiata)

The radiated tortoise (Geochelone radiata) is an endangered species endemic to the spiny forest of southern Madagascar. The main threat that this species faces is illegal harvesting for both local consumption and foreign markets. Large numbers of live individuals are often confiscated and their population of origin is in most cases unknown. Previous work has identified three genetically distinct units across the current distribution of the species. The objective of the present study was to develop a method of assigning G. radiata individuals to their original population based on the analysis of morphometric characters. We measured 39 variables on the shell of tortoises sampled at seven locations across the species range in order to assess differentiation. We employed a PCA-based method to analyze morphometric data and found three distinct groups of populations based solely on shape variation. Discriminant functions allowed for the correct classification of 83% of individuals among these groups. The abundance of tortoises, a variable strongly linked to the level of human exploitation at each site, was correlated with the morphometric differentiation of populations. Our results thus suggest that humans may have played a role in the recent evolution of radiated tortoises. The outlined methodology could become a useful tool for the management of radiated tortoises, and could theoretically be applied to any chelonian species. (c) 2006 Elsevier Ltd. All rights reserved.