Inferring odontocete life history traits in dentine using a multiproxy approach (δ15 N, δ44/42 Ca and trace elements).

RATIONALE: 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. METHODS: Here, we present a multiproxy approach to investigate the use of Ca isotope compositions (δ44/42 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. RESULTS: To help interpret the dentine data, we provide milk elemental compositions and δ44/42 Ca values for two odontocete individuals. We discuss the observed changes in δ44/42 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 δ44/42 Ca values recorded in the early formed dentine. CONCLUSIONS: 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.

Exploring diet shifts and ecology in modern sharks using calcium isotopes and trace metal records of their teeth.

Sharks occupy all living environments of the marine realm as well as some freshwater systems. They display varied and flexible feeding behaviours, but understanding their diet remains challenging due to their elusive ecology and the invasiveness of stomach content analyses in regard of their threatened status. As a potential alternative, we discuss the variability in δ44/42 Ca values recorded in the tooth enamel of size-graded individuals belonging to three species of large sharks with distinct diets (Isurus oxyrinchus, Hexanchus griseus and Carcharodon carcharias). The preliminary results highlight shifts in diet linked to ontogeny (I. oxyrinchus and H. griseus) and spatial distribution (C. carcharias) characterizing feeding behaviour in these species at individual and population level. These outcomes agree with the results of traditional stomach analyses supporting that nontraditional stable isotopes thus represent new perspectives for the study of modern and extinct shark ecology. In addition, for the first time, the Sr/Ca elemental ratios measured in H. griseus reflect sexual differences that could be interpreted in terms of spatial segregation or physiological heterogeneities.

Absence of temperature effect on elution profiles on anionic and cationic ion-exchange resins from 4°C to 28°C.

RATIONALE: In labs devoted to the geochemistry of non-traditional isotopes, chemical elution is necessary to purify the element of interest. Elution is always performed in over-pressured and air-conditioned clean rooms. We took advantage of an air-conditioning failure in our lab during summer 2018 to study the effect of temperature on the characteristics of the elution profiles of ion-exchange resins. METHODS: We performed the ion-exchange separation of copper, iron and zinc on macroporous anionic AG MP-1 resin and that of calcium on cationic AG 50W-X12 resin, at 28°C, prior to the measurement of their isotopic ratios by mass spectrometry. We further performed these experiments in a clean hood in a cold room at 4°C. The elution curves were processed on biological standards, i.e. bovine liver (SRM-1577c), fetal bovine serum (FBS), bone meal (SRM-1486) and the seawater IAPSO standard. RESULTS: The elution profiles of major elements for each matrix, and those of copper, iron, zinc and calcium, were compared with those classically achieved at 20°C in air-conditioned conditions. The results show that the elution profiles preserve their characteristics whatever the temperature, suggesting that partitioning coefficients between resin and solution are thermo-independent in the range of temperature from 4°C to 28°C. CONCLUSIONS: If generalized to other matrices, notably inorganic, and to other elements, notably the extreme case of the separation of Rare Earth Elements, the present results suggest that clean labs may not have to be air-conditioned. This would reduce installation and operating costs and have a positive effect on the environment, paving the way for the development of a "green geochemistry".

Lactation and gestation controls on calcium isotopic compositions in a mammalian model.

Lactation and gestation are among the physiological events that trigger the most intense changes in body calcium (Ca) fluxes. Along with the composition of the animal 2021 diet, these events are suspected to impact the Ca isotopic composition of Ca body reservoirs but their dynamics are poorly understood. In this study, we monitored a group of domestic sows across a full reproduction cycle. We collected tissues and fluids (blood, urine, milk, colostrum, umbilical blood, adult and piglet bones) at different steps of gestation and lactation, and analyzed their Ca isotopic compositions (i.e. δ44/42Ca) by means of multi-collector inductively coupled plasma mass spectrometry. Among other results, we report the first observations of Ca isotopic fractionation between maternal and umbilical blood (Δ44/42Caumbilical blood-sow blood = -0.18 ± 0.11‰, n = 3). Our data also highlight that gestation and lactation periods are characterized by small diet-bone Ca isotopic offsets (Δ44/42Cabone-diet = -0.28 ± 0.11‰, n = 3), with 44Ca-enriched blood compositions during nursing (Δ44/42Canursing blood-gestation blood = $+ 0.42{\rm{\,\,}}_{ - 0.12}^{ + 0.11}$‰, n = 3). Under the light of an up-to-date mammalian box model, we explored different scenarios of gestation and lactation Ca fluxes experienced by a sow-like animal. These simulations suggest that gestation changes on body δ44/42Ca values may result from the intensification of Ca absorption by the animal, whereas the production of 44Ca-depleted milk is the main driver for the 44Ca enrichment in blood during lactation. In addition, our results also support that bone mineralization could be associated with a more restricted Ca isotopic fractionation than previously envisioned. Together, these results refine the framework of Ca isotope applications, notably regarding the monitoring of human bone balance and the study of species and ecosystems from the present and the past.