Complete mitochondrial genome of a Pleistocene jawbone unveils the origin of polar bear - PubMed (original) (raw)

. 2010 Mar 16;107(11):5053-7.

doi: 10.1073/pnas.0914266107. Epub 2010 Mar 1.

Stephan C Schuster, Yazhou Sun, Sandra L Talbot, Ji Qi, Aakrosh Ratan, Lynn P Tomsho, Lindsay Kasson, Eve Zeyl, Jon Aars, Webb Miller, Olafur Ingólfsson, Lutz Bachmann, Oystein Wiig

Affiliations

Complete mitochondrial genome of a Pleistocene jawbone unveils the origin of polar bear

Charlotte Lindqvist et al. Proc Natl Acad Sci U S A. 2010.

Erratum in

Abstract

The polar bear has become the flagship species in the climate-change discussion. However, little is known about how past climate impacted its evolution and persistence, given an extremely poor fossil record. Although it is undisputed from analyses of mitochondrial (mt) DNA that polar bears constitute a lineage within the genetic diversity of brown bears, timing estimates of their divergence have differed considerably. Using next-generation sequencing technology, we have generated a complete, high-quality mt genome from a stratigraphically validated 130,000- to 110,000-year-old polar bear jawbone. In addition, six mt genomes were generated of extant polar bears from Alaska and brown bears from the Admiralty and Baranof islands of the Alexander Archipelago of southeastern Alaska and Kodiak Island. We show that the phylogenetic position of the ancient polar bear lies almost directly at the branching point between polar bears and brown bears, elucidating a unique morphologically and molecularly documented fossil link between living mammal species. Molecular dating and stable isotope analyses also show that by very early in their evolutionary history, polar bears were already inhabitants of the Artic sea ice and had adapted very rapidly to their current and unique ecology at the top of the Arctic marine food chain. As such, polar bears provide an excellent example of evolutionary opportunism within a widespread mammalian lineage.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Fig. 1.

Metagenomic composition of the 454 sequence reads from the Poolepynten polar bear tooth. The pie chart shows the percentages of sequence reads assigned to the categories bacteria, bear endogenous, human, Archaea, and other sources. A comparison of the 454 sequence reads against the dog genome suggested that ∼40% of the reads represent endogenous bear DNA, whereas 4.5% and the remaining ∼55% represent human and bacterial contamination, respectively.

Fig. 2.

Fig. 2.

Mitogenomic sequence variation and organization. Sequence differences found among 17 bear mitochondrial genomes with respect to a previously published polar bear genome (GenBank accession no. NC_003428). Each vertical bar depicts a nucleotide difference from this reference sequence (shown at the bottom illustrating the organization of the genome into the different regions). The ancient Poolepynten bear sequence is highlighted in red.

Fig. 3.

Fig. 3.

Phylogenetic and chronographic reconstruction of polar bear evolution. (A) Maximum clade probability tree inferred from a BEAST analysis of complete mt genome sequences excluding the VNTR repeat in the D loop (

Table S2

). Numbers at selected nodes indicate mean ages in million years. The red bars at nodes illustrate the age width of the 95% highest posterior density interval. The posterior probability values of each clade are indicated in orange. An identical tree topology was obtained using maximum parsimony and maximum likelihood (bootstrap support values in green and yellow, respectively). For details on voucher information for the mtDNA genome sequences included in this study, see

Table S1

and

Figs. S3

and

S4

. The 2009 Geologic Time Scale with major relevant epochs is shown above the tree. (B) Phylogenetic network of complete mt genomes (excluding the VNTR repeat) of 11 polar and brown bears based on Neighbor-Net analysis with LogDet distances (see scale bar).

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