Polar bears, by Alan D. Wilson (naturespicsonline.com: [1]) [CC-BY-SA-3.0 (www.creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Here’s something for the lovers of cute fluffy white mammals: a new study in science lead by Frank Hailer uses nuclear markers to infer the time at which polar bears split up from their ancestral brown bear lineage. Previous analysis, based on mitochondrial DNA, placed this time around the late Pleistocene. The new study, which uses nuclear markers, more precisely “9116 nucleotides from 14 independent nuclear loci (introns) across the genome in 45 individuals of polar, brown, and black bears”, shows that the time of divergence was likely much earlier, in the middle Pleistocene, about 600 (338 to 934) thousand years ago, with evidence for gene flow from the brown bear to the polar bear population which might in part explain the problems with the mtDNA. Interesting stuff, and water on the mills of people who have recently raised doubts about the use of mtDNA.
Hailer, F., Kutschera, V. E., Hallström, B. M., Klassert, D., Fain, S. R., Leonard, J. A., Arnason, U. & Janke, A. (2012) Nuclear Genomic Sequences Reveal that Polar Bears Are an Old and Distinct Bear Lineage. Science, 336, 344-347.
theoretical ecology 