DNA amplification success in historical samples. a) The longest allele (in base-pairs) amplifying at each locus plotted against the sample age. The size of the symbol indicates the number of samples for which genotyping was attempted at specific loci, and the pie charts give the proportion of samples that successfully amplified (white). Isoclines are given for the amplification success predicted by the GLM model, including sample age and maximum allele length as factors. The amplification success depended on the maximum allele length at the particular locus (χ2 = 427.78, df = 1, P < 0.0001), the age of the sample (χ2 = 54.47, df = 1, P < 0.0001) and the interaction between the two (χ2 = 51.65, df = 1, P < 0.0001). b) The 20 microsatellite markers tested in the study and their observed allele ranges. Only loci with amplification success > 80% were used for the temporal study, corresponding to maximum allele sizes below 166 base pairs (below the dashed line).