Patterns of trace elements deposition in Indo-Pacific humpback dolphin (Sousa chinensis) teeth reflect early life...

Understanding early life history events within a population is imperative for developing effective conservation and management practices, particularly for vulnerable species in degraded environments with high environmental variability. Here, we first investigated the lifetime record of trace element (TE) accumulation in the teeth of Indo-Pacific humpback dolphins from the Pearl River Estuary, China, using in-situ laser ablation-inductively coupled plasma-mass spectrometry microanalysis, and further explored the suitability of teeth TEs as bioindicators of critical life stages. A total of 26 TEs were detected in the teeth of eight dolphins, with concentrations ranging from 0.003 ± 0.003 μg/g (Be) to 522,405.9 ± 44,690.3 (Ca) μg/g. The varied TE composition in teeth of the dolphins may be related to environmental exposure or the species-specific accumulation of TEs. Generalized linear mixed models showed that the accumulation of nearly half of the detected TEs (V, Fe, Co, Zn, Ga, As, Mo, Sn, Sb, Ba, and Bi) in the dolphin teeth is sex-specific. Temporal analyses revealed that the concentrations of Cu, As, Sr, Ba, and Bi demonstrate age-related changes in metabolic demands and elimination efficiency. Notably, the ratios of Ba/Ca and Sr/Ca in teeth of the dolphins exhibited clear physiological signals, which reconstructed the time of weaning (3-4 years of age). Moreover, the trends in the ratios of Zn/Ca suggest that female dolphins may reach sexual maturity at 9-11 years of age. These findings provide insights into marine mammal development, emphasizing the need for further research on TE accumulation mechanisms and ecological impacts.