Strontium Uptake and Intra-Population 87Sr/86Sr Variability of Bones and Teeth—Controlled Feeding Experiments With Rodents (Rattus norvegicus, Cavia porcellus)

Michael Weber,Théo Tacail,Regina Mertz-Kraus,Daniela E Winkler,Jennifer Leichliter,Katrin Weber,Federico Lugli,Marcus Clauss,Thomas Tütken

doi:10.3389/fevo.2020.569940

Abstract

Strontium isotopes in biogenic apatite, especially enamel, are widely employed to determine provenance and track migration in palaeontology and archaeology. Body tissues record the 87Sr/86Sr of bioavailable Sr of ingested food and water. To identify non-local individuals, knowledge of the 87Sr/86Sr of a non-migratory population is required. However, varying factors such as tissue turnover rates, feeding selectivity, Sr content, digestibility of food, and the ingestion of mineral dust can influence body tissue 87Sr/86Sr. To evaluate the Sr contribution of diet and water to mammalian hard tissues 87Sr/86Sr, controlled feeding studies are necessary. Here we present 87Sr/86Sr from controlled feeding experiments with two rodent species (Rattus norvegicus, Cavia porcellus). Due to the continuous and fast incremental growth of rat and guinea pig incisors (~0.1 – 0.5 mm/day), their enamel is expected to record isotopic dietary changes. For Experiment-1: Diet Switch, animals were switched from their respective supplier food to a pelleted experimental diet containing either insect-, plant-, or meat-meal and a staggered-sampling approach was used to monitor the 87Sr/86Sr changes in rat incisor enamel and bone over the course of the experiment. In Experiment-2: Basic Diets, separated cohorts (n = 6) of rats and guinea pigs were fed one of the three pelleted diets and received tap water for 54 days. While the rat incisors showed a complete tissue turnover, the slower-growing guinea pig incisors partially retained supplier diet-related isotopic compositions. In addition, one group of rats fed plant-meal pellets received Sr-rich mineral water, demonstrating that drinking water can be an important Sr source in addition to diet. Additionally, a leaching experiment showed that only a small fraction of diet-related Sr is bioavailable. Finally, in Experiment-3: Dust Addition, guinea pigs were fed pellets with and without addition of 4% of isotopically distinct dust (loess or kaolin). Animals that received kaolin-containing pellets displayed increased enamel 87Sr/86Sr. Intra-population 87Sr/86Sr variability within each feeding group was small and thus we conclude that it should not affect interpretations of 87Sr/86Sr in provenance studies. However, the differences between bulk food and leachate 87Sr/86Sr highlight the importance of Sr bioavailability for provenance studies and Sr isoscapes.

Highlights

The number of studies dealing with the radiogenic Sr isotope ratio (87Sr/86Sr) have substantially increased within the past decades, and it has become an important tool in many scientific fields, such as petrology, palaeoclimatology, forensics and food traceability, especially in combination with light stable isotopes (e.g., McArthur et al, 2001, 2012; Kelly et al, 2005; Kimura and Chang, 2012; Marchionni et al, 2016; Weber et al, 2018b)
Our controlled feeding experiment offered a unique possibility to evaluate the timing of Sr incorporation in tooth enamel, as well as the influence of diet-derived Sr on the 87Sr/86Sr of hard tissues of rodents
Our data provide a minimum estimate of the 87Sr/86Sr variability within a population, and highlight the importance of proper sampling strategies in building local isotopic baselines using rodents

Summary

Introduction

The number of studies dealing with the radiogenic Sr isotope ratio (87Sr/86Sr) have substantially increased within the past decades, and it has become an important tool in many scientific fields, such as petrology, palaeoclimatology, forensics and food traceability, especially in combination with light stable isotopes (e.g., McArthur et al, 2001, 2012; Kelly et al, 2005; Kimura and Chang, 2012; Marchionni et al, 2016; Weber et al, 2018b). The mineral composition of bone and tooth enamel is hydroxylapatite [Ca5(PO4)3(OH)], and the Ca2+ in the hydroxylapatite is substituted by Sr2+ in trace amounts due to their similar chemical behavior (Comar et al, 1957), making the determination of Sr isotope ratios in these materials feasible. Observed differences in 87Sr/86Sr in nature are related to differences in the relative abundance of the radiogenic 87Sr vs the stable 86Sr, due to the decay of the radioactive parent isotope 87Rb in geological materials (Banner, 2004). For radiogenic Sr (87Sr/86Sr), natural mass-dependent fractionation (Urey, 1947), as well as fractionation during mass spectrometric Sr isotope analysis are corrected for after normalization to a constant 88Sr/86Sr of 8.375209 during data reduction (Meija et al, 2016)

Methods

Results

Discussion

Conclusion