Fig. 1: Preservation assessment of dental calculus samples.

A SourceTracker analysis of species tables. Each bar represents a sample, coloured by the proportion of each contributing source (sources are the same as in (B)). B PCA of well-preserved calculus from the Pacific islands (blue) with samples from the same sources used in SourceTracker analysis plus additional ancient calculus. C Map of the islands from which samples were collected for this study, with the island name, number of collected samples, and age of the site. Pie charts indicate the fraction of samples from each site that were considered well-preserved, and are coloured by age of the site. Map was produced using the R packages ggmap, plotly, and sf. D Comparison of endogenous oral bacterial DNA and human host DNA in samples with environmental conditions on the islands that may affect DNA preservation. No associations between preservation of either oral bacterial DNA or human host DNA were found with any of the measured environmental factors by ANOVA; values for groups with < 3 samples should be considered unreliable. Boxes show data median, interquartile range (25th–75th percentile) and whiskers indicate minimum and maximum values. E Comparison between the Pacific/ISEA and northern Europe (England/the Netherlands) of the percentage of endogenous oral microbiome DNA in ancient dental calculus and human DNA in bones/teeth. Scale is logarithmic. The number of samples in each group is indicated next to the bars. Ancient dental calculus contains high levels of endogenous oral bacterial DNA in the Pacific/ISEA similar to that seen in northern Europe, in contrast to the lower levels of preserved human DNA in bones/teeth from the Pacific islands compared to northern Europe. Arch. bone - archaeological bone; Anc. calculus - ancient calculus; Mod. calculus - modern calculus.