title: Ancient hybridization and an Irish origin for the modern polar bear matriline.
abstract: BACKGROUND
  Polar bears (Ursus maritimus) are among those species most susceptible to the rapidly changing arctic climate, and their survival is of global concern. Despite this, little is known about polar bear species history. Future conservation strategies would significantly benefit from an understanding of basic evolutionary information, such as the timing and conditions of their initial divergence from brown bears (U. arctos) or their response to previous environmental change.
  
  
  RESULTS
  We used a spatially explicit phylogeographic model to estimate the dynamics of 242 brown bear and polar bear matrilines sampled throughout the last 120,000 years and across their present and past geographic ranges. Our results show that the present distribution of these matrilines was shaped by a combination of regional stability and rapid, long-distance dispersal from ice-age refugia. In addition, hybridization between polar bears and brown bears may have occurred multiple times throughout the Late Pleistocene.
  
  
  CONCLUSIONS
  The reconstructed matrilineal history of brown and polar bears has two striking features. First, it is punctuated by dramatic and discrete climate-driven dispersal events. Second, opportunistic mating between these two species as their ranges overlapped has left a strong genetic imprint. In particular, a likely genetic exchange with extinct Irish brown bears forms the origin of the modern polar bear matriline. This suggests that interspecific hybridization not only may be more common than previously considered but may be a mechanism by which species deal with marginal habitats during periods of environmental deterioration.
authors: Smurfit Institute of Genetics, Trinity College, University of Dublin, Dublin, Ireland.
authors: Ceiridwen J
authors: CJ
authors: Edwards
authors: Marc A
authors: MA
authors: Suchard
authors: Philippe
authors: P
authors: Lemey
authors: John J
authors: JJ
authors: Welch
authors: Ian
authors: I
authors: Barnes
authors: Tara L
authors: TL
authors: Fulton
authors: Ross
authors: R
authors: Barnett
authors: Tamsin C
authors: TC
authors: O'Connell
authors: Peter
authors: P
authors: Coxon
authors: Nigel
authors: N
authors: Monaghan
authors: Cristina E
authors: CE
authors: Valdiosera
authors: Eline D
authors: ED
authors: Lorenzen
authors: Eske
authors: E
authors: Willerslev
authors: Gennady F
authors: GF
authors: Baryshnikov
authors: Andrew
authors: A
authors: Rambaut
authors: Mark G
authors: MG
authors: Thomas
authors: Daniel G
authors: DG
authors: Bradley
authors: Beth
authors: B
authors: Shapiro
mesh_terms: D000818:Animals; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D010802:Phylogeny; D001503:Ursidae