Inferring odontocete life history traits in dentine using a multiproxy approach (δ¹⁵ N, δ^44/42 Ca and trace elements)

Understanding the interactions between marine mammals and their environment is critical for ecological and conservation purposes. Odontocetes offer a continuous record of their life history from birth as recorded in annual increments of their tooth dentine. Because dentine is not remodeled and contains collagen, nitrogen stable isotope compositions (δ¹⁵ N) reflect nursing and weaning events, life history traits that would otherwise be impossible to retrieve in such elusive marine animals. Yet, capturing the magnitude and temporal changes in these events is constrained by tooth size and sampling resolution. Moreover, historical and fossil specimens undergo collagen decay, hence the need to develop the measurements of other proxies.

Here, we present a multiproxy approach to investigate the use of Ca isotope compositions (δ^44/42 Ca) in relation to δ¹⁵ N and laser ablation profiles for different trace metal (Ba, Mg, Sr, Zn) concentrations across the dentine of a single individual of the common bottlenose dolphin Tursiops truncatus.

To help interpret the dentine data, we provide milk elemental compositions and δ^44/42 Ca values for two odontocete individuals. We discuss the observed changes in δ^44/42 Ca across the dentine as potential markers of birth, weaning interval, incidental ingestion of seawater, trophic level and physiology. Incidental ingestion of seawater during nursing induces a positive offset in δ^44/42 Ca values recorded in the early formed dentine.

Life history parameters of individual marine mammals are extremely difficult to retrieve due to limitations in observing specimens in the wild and the methodology presented here offers new ecological and paleoecological perspectives.