[Taxacom] Polar bears as subspecies or species

Kenneth Kinman kennethkinman at webtv.net
Thu Jan 22 21:04:03 CST 2009


Hi Fred,
      I would agree that "laboratory" hybridization experiments are
suspect (often not reflecting what actually occurs in nature).  However,
I found that there are certainly some good examples of a "ring of
subspecies" (a.k.a. Rassenkreis) among reptiles.  See below for a link
to a map showing the way in which Ensatina oregonensis wraps around both
sides of the central California mountains (and then act like separate
species where they meet in southern California).  If the northern
California populations died out, you would actually have three separate
species in that case (two in California, and a third up in Oregon and
Washington).  The western United States might also be a more likely
place to finds similar rings of subspecies among amphibians (although
there might be cases where the circle of subspecies wrap around the
Appalachian Mountains).                                                                       
       A very commonly cited example of a circle of subspecies is within
the circumpolar gulls of the Larus argentatus-fuscus complex.  I suspect
there is still gene flow between these populations, but nowadays it is
more popular to split them into separate species.  This sort of reminds
me of how they used to regard grizzly bears of the New World as a
separate species from the Old World brown bears (although not
approaching the extreme splitting of grizzly bears).                       

     I think much of this has been in recent decades fed in part by
strict cladists' knee-jerk reactions to any suggestion that a species
might be paraphyletic, resulting in the splitting of the paraphyletic
mother species (although some of them take the alternate route of
overlumping the mother species with any daughter species).                            

      I am frankly concerned that strict cladists might be tempted to
lump polar bears into brown bears, simply because brown bears are
clearly paraphyletic with respect to polar bears.  But if polar bears
are clearly shown to be a separate species, strict cladists might then
be tempted to prevent the paraphyly by oversplitting brown bears into a
number of separate species.  I don't think either of those approaches
(both being anti-paraphyly for its own sake) is helpful.    

             -----------Ken Kinman

Link to Ensatina oregonensis example of a circle of subspecies
(Rassenkreis):
http://www.mun.ca/biology/scarr/2900_Ensatina_rassenkreis.htm

****************************************************
Fred wrote:
      I fear that this may be a memory of Moore's studies of laboratory
hybridization of Leopard Frogs in the 1940's. In the 1960's these
populations were shown to be divided into several perfectly good species
(though with grizzly x polar bear-like levels of hybridization among
some peripatric species pairs).





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