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

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.