New Genomic Resources Reveal Rapid Diversification and Ancient Gene Flow Among Bear Species

Strategic Insights -

A team of researchers at the University of California Santa Cruz has made significant contributions to the field of genome biology by reconstructing the evolutionary history of bears. The study, published in the journal Genome Biology and Evolution, presents chromosome-scale genomes for three additional bear species: the sun bear, sloth bear, and spectacled bear. By analyzing these genomes, the researchers found evidence of a rapid diversification of bears, with a 19 Ma origin for all bears and a 3.3 Ma origin for the six species of the subfamily Ursinae. The study also revealed a significant early hybridization event within Ursinae, resulting in conflicts between gene tree topologies and the highly supported species tree.

Key Takeaways:

  • The study presents chromosome-scale genomes for three additional bear species: the sun bear, sloth bear, and spectacled bear.
  • The researchers used a whole-genome alignment of all bear species and other carnivores to reconstruct the evolution of Ursidae.
  • The study found a rapid diversification of bears, with a 19 Ma origin for all bears and a 3.3 Ma origin for the six species of the subfamily Ursinae.
  • A significant early hybridization event within Ursinae was identified, resulting in conflicts between gene tree topologies and the highly supported species tree.
  • The ancestral karyotype of Ursinae has remained largely conserved with the ancestral karyotype of all bears over roughly fifteen million years.
  • The study identified species-specific evidence for positive selection on genes associated with color, diet, and metabolism.
  • One of these genes, TCPN2, has a role in pigmentation and shows a series of amino acid mutations in the polar bear over the last 0.5 Ma.

Statistics:

  • 19 Ma: The estimated age of origin for all bears.
  • 3.3 Ma: The estimated age of origin for the six species of the subfamily Ursinae.
  • 50%: The proportion of gene tree topologies that conflict with the highly supported species tree.
  • 15 million years: The time period over which the ancestral karyotype of Ursinae has remained conserved.
  • 0.5 Ma: The time period over which the polar bear shows a series of amino acid mutations in the TCPN2 gene.

Sources:

  • Genome Biology and Evolution. Chromosome-scale genomes show rapid diversification and ancient gene flow among bear species. 2025.
  • NewsRx. Researchers at University of California Santa Cruz Target Genome Biology and Evolution (Chromosome-scale genomes show rapid diversification and ancient gene flow among bear species). Life Science Weekly. October 21, 2025; p 5853.