Identification of stress from incremental dentine stable isotope trends using linear enamel hypoplasia

High-precision sampling of dentine serial increments facilitates analysis of short-term variations in stable isotope ratios. Temporal resolution of micro-sampled increments is sufficiently high that the impact of short-term periods of physiological stress, which have well-described effects on stable isotope ratios, may be captured. However, distinguishing the effects of diet vs physiological effects on δ13C and δ15N is non-trivial. This study presents a comparative analysis of one manifestation of physiological stress, linear enamel hypoplasia (LEH), and incrementally sampled dentine stable isotope ratios. Incidence and age at formation of LEH of 32 permanent canines from two medieval Croatian populations (13th-16th centuries CE cemeteries at Dugopolje and Udbina) were recorded. The canines were subsequently micro-sampled for δ13C and δ15N measurement. Intra-observer tests of δ13C and δ15N scatterplot interpretation were undertaken to investigate consistency in the identification of stress vs diet effects on stable isotope ratio trends. A strong relationship was found between stress-related variation in stable isotope trends and LEH. It is therefore proposed here that evaluation of teeth for LEH, and where identified, the recording of age of formation, become a standard component of incremental dentine stable isotope analysis pre-treatment protocols to improve stress identification in serially sampled dentine stable isotope ratio trends to enhance interpretations of past diet and individual isotope biographies.