title: Complete mitochondrial genome of a Pleistocene jawbone unveils the origin of polar bear.
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.
authors.affiliation: Department of Biological Sciences, University at Buffalo, Buffalo, NY 14260, USA. cl243@buffalo.edu
authors.forename: Charlotte
authors.initials: C
authors.lastname: Lindqvist
authors.forename: Stephan C
authors.initials: SC
authors.lastname: Schuster
authors.forename: Yazhou
authors.initials: Y
authors.lastname: Sun
authors.forename: Sandra L
authors.initials: SL
authors.lastname: Talbot
authors.forename: Ji
authors.initials: J
authors.lastname: Qi
authors.forename: Aakrosh
authors.initials: A
authors.lastname: Ratan
authors.forename: Lynn P
authors.initials: LP
authors.lastname: Tomsho
authors.forename: Lindsay
authors.initials: L
authors.lastname: Kasson
authors.forename: Eve
authors.initials: E
authors.lastname: Zeyl
authors.forename: Jon
authors.initials: J
authors.lastname: Aars
authors.forename: Webb
authors.initials: W
authors.lastname: Miller
authors.forename: Olafur
authors.initials: O
authors.lastname: Ingólfsson
authors.forename: Lutz
authors.initials: L
authors.lastname: Bachmann
authors.forename: Oystein
authors.initials: O
authors.lastname: Wiig
mesh_terms: D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D014644:Genetic Variation; D054629:Genome, Mitochondrial / Q000235:genetics*; D007568:Jaw / Q000033:anatomy & histology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D013997:Time Factors; D001503:Ursidae / Q000033:anatomy & histology* / Q000235:genetics*