There are clues that calcium (Ca) isotope composition of vertebrate bioapatite is influenced by diet and trophic level. These clues however conflict with several cases of mammal species exhibiting Ca isotope compositions which are inconsistent with their trophic levels. These observations support that diet may not be the only factor driving the Ca isotope composition in mammalian enamel and bone. To investigate this question, we selected a modern Cervus elaphus population (Bauges Natural Regional Park, Alps, France) to serve as a model for Ca isotope physiology of cervids and other mammals. Subsequently, we reinvestigated the case of the fossil Rangifer tarandus population from Jaurens (Late Pleistocene locality, 32.6 to 29.7 kyr BP, France), a population for which abnormal 44Ca-depleted isotope compositions (regarding the low trophic level of reindeers) have been previously documented. By combining bone samplings and serial enamel micro-samplings, we discuss the main potential sources of Ca isotopic variability in bioapatite of young and adult individuals. This includes the effects of gestation, lactation, antlerogenesis, browser-grazer ecologies, osteophagia and natural mineral licks. Our results suggest an important effect of lactation on bone Ca isotope composition (δ44/42Ca = +0.19 ± 0.09‰; 95% confidence interval), whereas other factors such as gestation or antlerogenesis seem more secondary. Our enamel micro sampling method allowed to detect when enamel Ca isotope composition could be affected by milk consumption or mineral supplementation. Thanks to these advances, we collected new data from the Pleistocene reindeers of Jaurens, which are now consistent with their known low trophic level and plant-based diet. This demonstrates that disentangling ecological and physiological signals within enamel Ca isotope compositions is possible by using serial micro-sampling. This approach allows retrieving accurate trophic information from this proxy and truly pushes forward the limits of Ca isotope applications regarding paleoecology, physiology and ethology.
This research was supported by the TelluS program of CNRS/INSU (DIUNIS project to JEM) and ENS de Lyon. We thank D. Mollex for his help regarding thin section preparation, D. Berthet for allowing access to the specimen curated in the collections of the Musée des Confluences, Lyon, and E. Robert for allowing access to Jaurens specimens curated in the paleontological collections of the LGL-TPE. We would like to thank the OGFH, the Groupement d'Intérêt Cynégétique des Bauges, the Office National des Forêts, as well as the hunters and professionals from the OFB (ex-ONCFS; T. Chevrier and T. Amblard) who contributed to collect red deer data in Bauges NRP. Finally, we thank the two anonymous reviewers, as well as the editors T. Tütken and T. Algeo for their detailed comments that helped to considerably improve the initial version of this work.
- Stable isotopes
- Mineral supplementation