Ancient DNA identifies post-glacial recolonisation, not recent bottlenecks, as the primary driver of contemporary mtDNA phylogeography and diversity in Scandinavian brown bears

Authors

  • Sarah C.E. Bray,

    1. Australian Centre for Ancient DNA, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA, Australia
    Search for more papers by this author
    • These authors contributed equally to this work.
  • Jeremy J. Austin,

    Corresponding author
    1. Sciences Department, Museum Victoria, Carlton Gardens, Melbourne, Vic, Australia
    • Australian Centre for Ancient DNA, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA, Australia
    Search for more papers by this author
    • These authors contributed equally to this work.
  • Jessica L. Metcalf,

    1. Australian Centre for Ancient DNA, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA, Australia
    2. Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA
    Search for more papers by this author
  • Kjartan Østbye,

    1. Department of Biology, Centre for Ecological and Evolutionary Synthesis (CEES), University of Oslo, Oslo, Norway
    2. Department of Forestry and Wildlife Management, Hedmark University College, Elverum, Norway
    Search for more papers by this author
  • Eivind Østbye,

    1. Department of Biology, University of Oslo, Oslo, Norway
    Search for more papers by this author
  • Stein-Erik Lauritzen,

    1. Department of Earth Science, University of Bergen, Bergen, Norway
    Search for more papers by this author
  • Kim Aaris-Sørensen,

    1. Centre for GeoGenetics, Natural History Museum of Copenhagen, University of Copenhagen, Copenhagen Ø, Denmark
    Search for more papers by this author
  • Cristina Valdiosera,

    1. Centro Mixto, Universidad Complutense de Madrid–Instituto de Salud Carlos III de Evolucion y Comportamiento Humanos, Madrid, Spain
    Search for more papers by this author
  • Christina J Adler,

    1. Australian Centre for Ancient DNA, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA, Australia
    2. Faculty of Dentistry, University of Sydney, Sydney, NSW, Australia
    Search for more papers by this author
  • Alan Cooper

    1. Australian Centre for Ancient DNA, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA, Australia
    Search for more papers by this author

*Correspondence: Jeremy Austin, Australian Centre for Ancient DNA, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA 5005, Australia.

Email: Jeremy.austin@adelaide.edu.au

Abstract

Aim

Brown bear populations in Scandinavia show a strong mitochondrial DNA (mtDNA) phylogeographic structure and low diversity relative to other parts of Europe. Identifying the timing and origins of this mtDNA structure is important for conservation programs aimed at restoring populations to a natural state. Therefore, it is essential to identify whether contemporary genetic structure is linked to post-glacial recolonisation from divergent source populations or an artefact of demographic impacts during recent population bottlenecks. We employed ancient DNA techniques to investigate the timing and potential causes of these patterns.

Location

Scandinavia and Europe.

Methods

Ancient mtDNA sequences from 20 post-glacial Scandinavian bears were used to investigate phylogeographic structure and genetic diversity over the last 6000 years. MtDNA from 19 Holocene Norwegian bears was compared with 499 sequences from proximate extant populations in Sweden, Finland, Estonia and western Russia. A single mtDNA sequence from a Holocene Denmark sample was compared with 149 ancient and modern bears from Western Europe.

Results

All nineteen Holocene Norwegian samples are identical to or closely related to the most common mtDNA haplotype found in northern Europe today. MtDNA diversity was low and not significantly different from extant populations in northern Europe. In Denmark, we identified a single mtDNA haplotype that is previously unrecorded from Scandinavia.

Main conclusions

The current discrete phylogeographic structure and lack of mtDNA diversity in Scandinavia is attributed to serial founder effects during post-glacial recolonisation from divergent source populations rather than an artefact of recent anthropogenic impacts. In contrast to previous interpretations, the recolonisation of southern Scandinavia may not have been limited to bears from a single glacial refugium. Results highlight the importance of conserving the long-term evolutionary separation between northern and southern populations and identify southern Scandinavia as an important reservoir of mtDNA diversity that is under threat in other parts of Europe.

Ancillary