semi-species

[Ken Kinman]

    I don't recall the exact definition of a semi-species, but is a
basically a species caught in the process of becoming two separate species,
but not enough divergence has occurred for "isolating mechanisms" (my
apologies to Ernst Mayr for using that phrase) to be perfected.
    I believe Les Kaufman (here on Taxacom if I recall correctly) once
referred to this as "webbing at the node", which is a pretty good way to get
the idea across how "messy" speciation can be, being the continuous process
that it is (except perhaps for allopolyploidy).
     Semi-species are probably usually formed when two "incipient species"
come back into contact before speciation is complete, and massive secondary
hybridization occurs where they come together.  Presumably a lot of this
kind of thing happens at the end of Ice Ages, but retreating ice is just one
of many potential scenarios that can trigger the genetic introgression by
which semi-species can be recognized.   Perhaps others could explain this
more fully than I.
                  --------Ken Kinman

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