The cave bear’s hibernation: reconstructing the physiology and behaviour of an extinct animal

Abstract

When studying an extinct species such as the cave bear (Ursus spelaeus ROSENMÜLLER 1794), it is possible to apply a variety of molecular biology techniques such as the study of stable isotopes or mitochondrial DNA (mDNA) to infer patterns of behaviour or physiology that would otherwise remain concealed. Throughout Europe and along time, differences in the isotopic values (δ¹³C and δ¹⁵N) of cave bears arise from environmental differences and the Pleistocene climatic evolution. The climate determines the hibernation length, during which the cave bears undergo a particular physiology that can be related to an increase in δ¹⁵N during climate cooling. In order to verify whether hibernation affected the isotopic values, we compared cave bears in different ontogenetic stages. The results show that perinatal values reflect the values for mothers during hibernation, while juveniles show differences in maternal investment. A previous study in the literature based on complete mitochondrial DNA sequences of several individuals collected from closely situated caves showed that each cave housed, almost exclusively, a single lineage of haplotypes. This pattern suggests extreme fidelity to the birth site, or homing behaviour, and that cave bears formed stable maternal social groups, at least for the purpose of hibernation. Studies of this type offer unexpected data on the palaeobiology of this extinct animal.

Keywords:

• Ursus spelaeus
• metabolism
• stable isotopes
• ancient DNA
• homing behaviour

Acknowledgements

We would like to thank Dr. Anneke Von Heteren and Dr. Borja Figueirido for the invitation to participate in this volume that is dedicated to recent research on the cave bear, and which is the fruit of the symposium held in Munich in August 2017 during the 15th Annual Meeting of the Association of European Vertebrate Palaeontologists. The study of neonate cave bears and the comparison of isotopes of European cave bears is part of the PhD thesis of MPR. Three anonymous reviewers contributed largely to improve the first version of the manuscript. The authors thank Dr. I. Martini, Dr. J. Maroto and Dr. G. Baryshnikov for providing some bone samples for the isotopic study, as well as the constant support of Dr. Marcos Vaqueiro and the entire Grupo Espeleolóxico A Trapa (Vigo-A Coruña) during the fieldwork in the caves of Galicia.