Gene Expression

Polar bears: a species?

Since everyone is talking about the fact that the Polar Bear how become a protected species, I thought I’d point to this cool study, Mitochondrial DNA Phylogeography of the North American Brown Bear and Implications for Conservation. Additionally, check out the figure below….

i-a433bd19c46e2ddbce327b8ce1cc1de3-polarbears.jpg

Comments

  1. #1 Homie Bear
    May 15, 2008

    Yeah I’ve heard this before, that the Grizzlies of the ABC islands are closer genetically to polar bears than to mainland grizz. Makes sense, really.
    And then, if you grant U. maritimus its own species designation, would that make it one of the youngest species of mammals on the planet? younger than H. sapiens by a long shot.

  2. #2 Greg Laden
    May 15, 2008

    I love this study. Polar bears are without a doubt a distinct species separate from brown bears. That is a fact.

    This study does not contradict that at all. Rather, it tells us something about what a specialization event can look like.

    Don’t you think?

  3. #3 razib
    May 15, 2008

    they’re an ecotype. as for whether they are a species or not, depends on what your ends are….

    (for the purposes of the ESA i’d say yes)

  4. #4 Josh Rosenau
    May 15, 2008

    Whether polar bears are a new species is a definitional question. They are (or were) on a unique phylogenetic trajectory, which some regard as speciation. They hybridize with grizzly bears, so they don’t necessarily recognize themselves as separate, and aren’t fully reproductively isolated.

    Fortunately, the Endangered Species Act doesn’t actually require that polar bears be a different species. The act clarifies that “the term ‘species’ includes any subspecies of fish or wildlife or plants, and any distinct population segment of any species of vertebrate fish or wildlife which interbreeds when mature.” And the polar bear is clearly such a “distinct population segment.”

  5. #5 Jim Thomerson
    May 15, 2008

    There is a joke, usually told in long form, where a baby polar bear askes his mother and father if he has any black bear, brown bear, sloth bear, panda bear, or spectacled bear blood. Each time they reassure him he is pure polar bear. Finally, the baby bear askes, “If I am pure polar bear, why am I cold?”

    So, the polar bear is a paraphyletic species.

  6. #6 razib
    May 15, 2008

    i heard the joke with a punch line, “cuz i’m fucking freezing!”

  7. #7 onleyone
    May 16, 2008

    oh, cool paper indeed, but i thought it was something new at first (no snipe intended). that paper wasn’t out long before a 1997 submission to Molecular Ecology — “Gene flow between insular, coastal and interior populations of brown bears in Alaska”, by Paetkau, Shields & Strobeck — questioned the findings, showing that there has indeed been relatively frequent gene flow between the ABC island brown bears and the mainland populations. here’s an abstract; i have a PDF myself, but can’t seem to put my hands on a good link at the moment….

  8. #8 onleyone
    May 16, 2008
  9. #9 MMOToole
    May 16, 2008

    It would be interesting to get mitochondrial data from Siberian browns (Eurasian brown bears are U. arctos, too) to see where they fit in all this: whether the grizzly clades we have are mostly related to bears that came across Beringia later, with the ABC Island/polar clade a remnant of an earlier population…or vice versa.

  10. #10 RPM
    May 16, 2008

    How much do you trust that topology? It comes from a single marker, so it should be taken with a grain of salt. mtDNA easily introgresses between populations. Also, I bet polar bears are monophyletic if you examine enough loci. I doubt brown bears are.

  11. #11 razib
    May 16, 2008

    How much do you trust that topology? It comes from a single marker, so it should be taken with a grain of salt. mtDNA easily introgresses between populations. Also, I bet polar bears are monophyletic if you examine enough loci. I doubt brown bears are

    i don’t trust it THAT much. i just think polar bears are a really cool illustration of the idea that species aren’t as cut & dried as you’d think….

  12. #12 RPM
    May 16, 2008

    Not as cut and dried as I think? Are you challenging my concept of species? How dare you!!??

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