Are mineralization anomalies in common dolphin teeth associated with life-history events and/or the exposure to anthropogenic pollutants?

The tooth histology of a total 22 and 95 short-beaked common dolphins (Delphinus delphis) from Scottish (UK) and Galician (Spain) waters, respectively, was examined to determine whether the incidence of mineralization anomalies could be related to certain stressful conditions linked with life-history events or to exposure to anthropogenic pollutants (i.e. Polychlorinated biphenyls and Dichlorodiphenyltrichloroethanes). Overall, the incidence of five categories of mineralization anomalies increased with age. Model results indicated that the presence of cemental disturbance increased with age, body length and sexual maturity in common dolphin from both areas. In addition, incidence of dentinal resorption and accessory lines increased with age and body length in Galician animals. The time course of appearance of dentinal resorption and cemental disturbance was similar to the time course of maturation suggesting a link between anomaly occurrence and the age at which the animals become sexually mature. There were two age ranges at which marker lines tended to appear: 1-2 and 6-8 years old, which coincided with the beginning of weaning and/or the age at sexual maturation, respectively, suggesting an association with these two major life-history events. Pulp stones were recorded in teeth of a few mature Galician dolphins (n = 4). No evidence was found that the presence of mineralization anomalies in dolphin teeth was significantly related to persistent organic pollutant concentrations in the blubber. Our results provide evidence that certain tooth mineralization anomalies could be interpreted as time markers associated with life-history events, potentially representing a powerful tool for long-term monitoring and modelling.