• DOI:10.1126/science.1216424
• Corpus ID: 12671275

Nuclear Genomic Sequences Reveal that Polar Bears Are an Old and Distinct Bear Lineage

@article{Hailer2012NuclearGS,
  title={Nuclear Genomic Sequences Reveal that Polar Bears Are an Old and Distinct Bear Lineage},
  author={Frank Hailer and Verena Esther Kutschera and Bj{\"o}rn Mikael Hallstr{\"o}m and Denise Klassert and Steven R. Fain and Jennifer A. Leonard and {\'U}lfur {\'A}rnason and Axel Janke},
  journal={Science},
  year={2012},
  volume={336},
  pages={344 - 347}
}

• F. Hailer, V. Kutschera, +5 authors A. Janke
• Published 20 April 2012
• Biology, Medicine
• Science

Ancient Bears Polar bears are well known for adapting to their cold Arctic climate. Some recent studies, based on mitochondrial DNA, concluded that they are a relatively young species and that these adaptations occurred quite quickly. Although mitochondrial DNA is regularly used to estimate evolutionary history, it has some well-known drawbacks, including sex-biased dispersal and hybridization. Thus, Hailer et al. (p. 344) looked at neutral genetic data that are distributed more widely across the genome of a relatively large sample of polar, brown, and black bears. Consistent with fossil-based studies, the analysis reveals polar bears as a sister lineage to all brown bears, with an estimated divergence time of 300,000 to 900,000 years ago. Thus, polar bears are indeed of a more ancient lineage, and more recent estimates based on mitochondrial DNA are likely to have been affected by past hybridization with brown bear. Genomic analyses show that polar bears as a species are older and genetically more distinct than previously estimated. Recent studies have shown that the polar bear matriline (mitochondrial DNA) evolved from a brown bear lineage since the late Pleistocene, potentially indicating rapid speciation and adaption to arctic conditions. Here, we present a high-resolution data set from multiple independent loci across the nuclear genomes of a broad sample of polar, brown, and black bears. Bayesian coalescent analyses place polar bears outside the brown bear clade and date the divergence much earlier, in the middle Pleistocene, about 600 (338 to 934) thousand years ago. This provides more time for polar bear evolution and confirms previous suggestions that polar bears carry introgressed brown bear mitochondrial DNA due to past hybridization. Our results highlight that multilocus genomic analyses are crucial for an accurate understanding of evolutionary history.