Résultats : Article 2

Article n°2 :

LOW REGIONAL DIVERSITY OF LATE CAVE BEARS MITOCHONDRIAL DNA AT THE TIME OF CHAUVET

AURIGNACIAN PAINTINGS. Bon C., Berthonaud V., Fosse P., Gély B., Maksud F., Vitalis R., Philippe M., van der Plicht J., Elalouf J.-M. Journal of Archaeological Science 38:1886-1895, 2011.

Low regional diversity of late cave bears mitochondrial DNA at the time of Chauvet Aurignacian paintings

Céline Bon^a, Véronique Berthonaud^a, Philippe Fosse^b, Bernard Gély^c, Frédéric Maksud^d, Renaud Vitalis^e, Michel Philippe^f, Johannes van der Plicht^{g, h}, and Jean-Marc Elalouf^a,*

aInstitut de Biologie et Technologies de Saclay, Service de Biologie Intégrative et Génétique Moléculaire, CEA Saclay, 91191 Gif-sur-Yvette cedex, France; ^bCNRS UMR 5608, Université Toulouse le Mirail, 31058 Toulouse cedex 1, France; ^cService régional de l'archéologie, DRAC Rhône-Alpes, 69283 Lyon, France; ^dService Régional de l’Archéologie, 32 rue de la Dalbade, BP811 31080 Toulouse cedex 6, France; ^eCNRS-INRA UMR CBGP (INRA—IRD—CIRAD—Montpellier SupAgro), Campus International de Baillarguet, CS 30016, F-34988 Montferrier-sur-Lez Cedex, France; ^fCentre de Conservation et d’Étude sur les Collections, 13A rue Bancel, 69007 Lyon, France; ^gRadiocarbon Laboratory, Groningen University, Nijenborgh 4, 9747 AG Groningen, Netherlands; ^hFaculty of Archaeology, Leiden University, P.O. Box 9515, 2300 RA Leiden, Netherlands.

*Address correspondence to:

Jean-Marc Elalouf

Institut de Biologie et Technologies de Saclay, Service de Biologie Intégrative et Génétique Moléculaire, CEA Saclay, 91191 Gif-sur-Yvette cedex, France

jean-marc.elalouf@cea.fr Tel: (33) 1 69088022 Fax: (33) 1 69084712

Key words: ancient DNA; Chauvet-Pont d’Arc Cave; Deux-Ouvertures Cave; mitochondrial D-loop; radiocarbon dating; Ursus spelaeus

Abbreviations: AMS, accelerator mass spectrometry; bp, base pair; BP, Before Present; GrA, Groningen laboratory code; numts, nuclear copies of mitochondrial sequences.

Data deposition footnote: The cave bear nucleotide sequences reported in this paper have been deposited in the GenBank database (accession numbers AY616447, AY836000, DQ398002 and HQ540348-HQ540359).

Abstract

The Chauvet-Pont d’Arc and Deux-Ouvertures caves, located along the Ardèche river (France), contain abundant remains of the extinct cave bear (Ursus spelaeus). Because they also display a variety of Palaeolithic anthropogenic evidences, such as the earliest charcoal drawings recorded to date (Chauvet-Pont d’Arc), and delicate engravings (Deux-Ouvertures), they offer the opportunity of studying the interaction between animals and human beings during a key period for Pleistocene species extinctions. We characterised cave bear specimens from these two sites by radiocarbon dating, stable isotopes, and mitochondrial DNA analysis.

In Chauvet-Pont d’Arc, we obtained radiocarbon ages that ranged between 29,000 and 37,300 years before present (BP). The Deux-Ouvertures cave bear specimens clustered to the bottom of this time frame, returning radiocarbon ages of 27,440 to 30,220 years BP. Cave bear nitrogen isotope values were all compatible with a vegetarian diet. Mitochondrial DNA analysis, carried out on a highly variable domain of the control region, evidenced only two cave bear haplotypes, including a new haplotype, and a common one which largely predominated. We detected both haplotypes in Chauvet-Pont d’Arc, but only recorded the predominant one in the Deux-Ouvertures Cave. Our data put forward the surprising observation that cave bears inhabited Ardèche over a short period of time, from about 37,000 to 27,400 years BP. They were notably present during the first (Aurignacian) phase of human intrusions in Chauvet-Pont d’Arc, 30,000 to 32,000 years BP. This points to the possible competition for cave sites, presumably on a seasonal scale considering the cave bear habit for hibernation. During this time period, the small number of haplotypes is at variance with the extensive genetic diversity reported elsewhere for much more ancient specimens.

1. Introduction

The cave bear (Ursus spelaeus) is one example of megafaunal species that, together with other carnivores (cave lion, cave hyena) and herbivores (woolly rhinoceros), became extinct during the late Pleistocene (Kurtén, 1976; Martin and Steadman, 1999; Stuart and Lister, 2007, 2010). Contrasting to other representative large Pleistocene mammals such as the woolly mammoth and giant deer, that were able to survive in limited areas up to 4,000-7,000 years BP (Stuart et al., 2004; Vartanyan et al., 1993), the cave bear mainly confined to Europe and was no longer present during the Holocene. The Ursus spelaeus diet is largely based on plant consumption, as shown by dental morphology (Kurtén, 1976) and stable isotope analysis of bone collagen, which most often yielded d¹⁵N values in the range of those found for vegetarian species (Bocherens et al., 1994). Occasional evidence of omnivory have been obtained from dental microwear analysis (Peigne et al., 2009) and unusually high d¹⁵N values of bone collagen (Richards et al., 2008), suggesting that the cave bear was more or less carnivorous depending on available resources and seasonality.

The fossil record indicates that Ursus spelaeus gradually evolved from Ursus deningeri, and abundant remains are available between 150,000 and about 28,000 years ago.

Palaeontological data also indicate that the cave bear and the brown bear (Ursus arctos) belong to different lineages, a notion which is further substantiated by ancient DNA analysis (Hänni et al., 1994; Loreille et al., 2001). Molecular dating analysis carried out using complete mitochondrial genomes of ancient and extant bears evaluated the divergence between the cave bear and brown bear lineages to 1.4-1.6 million years ago (Bon et al., 2008;

Lindqvist, et al., 2010).

The cave bear has long been considered to survive until the last millennia of the Pleistocene (Kurtén, 1976), a notion that has been questioned by Pacher and Stuart (Pacher and Stuart, 2009). These authors, who listed all available direct radiocarbon dates reported for Ursus spelaeus between 1971 and 2008, concluded that dates younger than 24,000 years BP were unreliable because of specimens misidentification (i.e. confusion between Ursus arctos and Ursus spelaeus) or technical pitfalls in the radiocarbon dating procedures. However, the possibility that the cave bear survived ten additional millennia is still considered and promoted a new series of studies in alpine refuges (Philippe et al., 2010). Thus, the exact timing of cave bear extinction is still a matter of debate. Consequently, the causes responsible for cave bear extinction are unclear and call for further studies.

In the present study, we focused on two sites of south-eastern France (Fig. 1) that both display a large number of cave bear remains and evidences of Palaeolithic human intrusions. One site corresponds to the Chauvet-Pont d’Arc Cave and contains the earliest rock art picture ever found, with charcoal drawings dating back to the Aurignacian period, 30,000 to 32,000 years BP (Valladas et al., 2001). Preservation of ancient DNA in this cave was demonstrated through the recovery of a complete cave bear mitochondrial genome from a 32,000-year-old specimen (Bon et al., 2008). The Deux-Ouvertures Cave is located 15 km downstream of Chauvet-Pont d’Arc along the Ardèche river. Rock art pictures in the Deux-Ouvertures consist in engravings ascribed to the upper Solutrean (Gély and Porte, 1996; Gély, 2005). In 2007, excavations carried out near these pictures yielded charcoal fragments as well as abundant cave bear remains (Philippe et al., 2009). We report here on the comparative analysis of the Chauvet-Pont d’Arc and Deux-Ouvertures cave bears with results on radiocarbon ages, stable isotopes, and mitochondrial DNA.