[Taxacom] Polar bears as subspecies or species

Kenneth Kinman kennethkinman at webtv.net
Thu Jan 22 17:05:47 CST 2009

Hi John,
        I would not be at all surprised that this occurs in some
amphibians and reptiles.  There are certainly such occurrences among
mammals and birds.                
        This "circle of subspecies" phenomenon is a wonderful example of
the fuzziness of speciation, as well as the role of historical
contingency.   Even though those populations at the extremes can no
longer breed when they come back together, there can still be gene flow
between them indirectly (via the intermediate populations).  It is still
one big species as long as this continues, even though they appear to
act like two species where the extremes come into contact (which can
fool naturalists studying them there).  However, if enough of the
intermediate populations die out, the gene flow is cut off permanently
and there are instead two separate species.  This is probably the
closest thing we have to true sister species (unlike paraphyletic mother
species giving rise to daughter species).                 
                            Ken Kinman                                        
John Grehan wrote,
      Even reproductive information may not introduce any greater
clarity. I recall (hopefully correctly) the case of a frog species in
the eastern us where adjacent populations can successfully interbreed,
but the frogs at each extreme of the range cannot.

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