Genetic variation of nuclear microsatellites assessed using STRUCTURE. Pie chart colours represent the proportional membership of individuals to microsatellite-based clusters inferred from the model for K = 7 (this model is well supported by Evanno et al. approach and provides detailed substructuring; see also Additional file 3). The dashed red line indicates the border between the Chefu and Limpopo haplogroups. The diameter of the pie charts is related to allelic richness (except the captive population GRZ, which is not scaled). Asterisks indicate populations with probable inbreeding (deficit of heterozygotes at four loci; Pop323 and Pop124); the red arrow indicates a population showing a significant bottleneck (Pop13); green arrow indicates secondary contact of two mtDNA lineages (Pop406).