Cladistics and "Eclecticism"

[Richard Jensen]

>
> The branch with two terminals
>                         ------B
>                   ---- |
>                         ------A
>
> now has three terminals
>
>                         ------B
>                   ---- |
>                         ------A
>                             |
>                              ---C

Since we're getting into improbable, but certainly not impossible, examples,
let's consider this.  In my example above, the isolated population (C) is the
result of autopolyploidy with a single propagule getting established and
founding the new population.  C has both morphological apomorphies (polyploidy
often yields these) and is a "good" biological species.  A, as a species-level
taxon, no longer exists.  So, we now have two species and let's suppose that for
the next two centuries C and A undergo separate evolutionary fates.  The
population of C begins to spread locally and some additional genetic apomorphies
evolve.  On the other hand, during the same time A experiences stabilizing
selection that results in no apomorphies that could be used to differentiate
extant A from A of 200 years ago.  Then, the habitat in which C is surviving
(ANWR?) is destroyed and C becomes extinct.  What is A now that C is extinct?
With no apomorphies to differemtiate it from its ancestor (pre-C A), it's still
A.  Would this be a case of extinction (as a taxon) not being forever?

Such a scenario may be occurring right now, given the fact that there are
instances of relatively recently derived auto- and allopolyploids that currently
have limited geographic ranges.

Dick
--
Richard J. Jensen              TEL: 219-284-4674
Department of Biology      FAX: 219-284-4716
Saint Mary's College         E-mail: rjensen at saintmarys.edu
Notre Dame, IN  46556     http://www.saintmarys.edu/~rjensen