Genetic and biochemical analysis of materials from a medieval population from Ynys Mon North Wales

Abstract

The archaeological excavation of the early medieval site at Towyn-Y-Capel on the island of Anglesey (Ynys Môn) in North Wales, UK, provided the opportunity to study a large population (122 skeletons) at a site that was in use over a period of up to 550 years (650 -1200 AD). Samples of skeletal materials for this study were taken directly from the site itself .The osteological condition of skeletal material was variable across the site. In general, the upper burials in particular were in the poorest condition, and were mainly fragmented and dispersed due to the ongoing site erosion and diagenetic processes. Conversely, lower “cist” burials were in far better condition.
The assessment of skeletal sample condition was used to select materials chosen for genetic analysis, and 44% (54) of the skeletal population were selected for analysis of appropriate samples of tooth and bone. The gross morphology of samples was assessed and 87% of bones and teeth were considered to be in good or fair condition, according to the gross preservation index (GPI) used, while only 2% of bones and no teeth were considered to be in excellent condition. In addition to GPI, a novel technique called Qualitative Light Fluoresence (QLF), based on autofluoresence, was used to ascertain the surface condition of the teeth. Compared to the fluorescence of modern enamel, there was a net loss of 21.8% fluorescence, although the degree of fluorescence from one sample to another varied (with a standard deviation from the mean of 24.973). Histological sections taken from non-human bone finds from the site generally varied less than that indicated by the gross morphology, showing good to excellent histological preservation.
Further to gross and histological morphology, ten skeletal samples were selected for detailed investigations, and were analysed for amino acid racemisation and amino acid composition. All samples tested had D/L enatomer Aspartic acid ratio less than 0.1, although 50% of the samples had D/L enatiomer Aspartic acid ratio over 0.08, which indicated that the recovery of aDNA from these skeletal samples was feasible, although the biological condition of the teeth was fairly degraded. The inorganic element profile of the same ten samples showed no discernable anomalies, either due to diet or diagenesis. To consolidate genographic research, strontium isotope analysis was performed and, from the small population subset, three anomalous ratios were found.
Two of these were high (Skeletons 33 and 60), indicating that these individuals had spent their childhoods in areas with high strontium ratios, representative of precambrian rock types, possibly older than those of the Holyhead Rock group, such as in Northern Scotland or Norway. The skeletal samples yielding the lowest strontium ratio (Skeleton 52) are of compelling interest, since the ratio is indicative of upbringing in only one place in the North Atlantic, namely Iceland.
In this study, DNA recovery was performed on teeth and bones from the site, after extensive decalcification of samples, and also extraction and optimisation trials. Amplification of DNA extracted from teeth samples was generally more successful than for bone samples. A random amplification based polymorphic (RAPD) DNA technique was utilised to “fingerprint” human and animal samples with limited success. Contamination and template variation are likely causes for the lack of success. Amplification using several primers specific for human HV1 & 2 mtDNA targets was also met with limited success. The results show that 14.8% of the skeletal teeth samples were amplified, and these were not commonly reproducible. DNA spiking trials demonstrated that some of the samples were affected by inhibition. Independent confirmation of 9 of 10 successful samples was attained by sequencing, and although sequences were highly degraded, an attempt was made at determining the haplogroups from the sequenced HV1 haplotypes based on likelihood. Generally, the site showed a high predominance of Haplotype K (5) followed by H (2) and U (2) haplogroup profiles.