[Taxacom] Phylogenetic Classification?

Stephen Thorpe s.thorpe at auckland.ac.nz
Fri Jul 31 20:02:10 CDT 2009

Re paraphyletic species: phylogenetics usually has species as terminal  
taxa, not individuals, in which case there is no such thing as a  
"paraphyletic species"...


Quoting Richard Zander <Richard.Zander at mobot.org>:

> This has come up once I think. Species paraphyly is generally considered
> something of a different thing than paraphyly of a genus. As far as I
> can figure it out, phylogeneticists expect a species that is
> paraphyletic (many exemplars with a different species coming out of the
> middle of the lineage of exemplars) to eventually become a sister group
> (reciprocally monophyletic is the phrase). Therefore, a paraphyletic
> species should be considered different from the autophyletic species
> because it will inexorably become a sister group to it as exemplars get
> their act together and homogenize their molecular data through
> recombination and gene conversion and whatnot.
> For the time being, however, I see the paraphyletic species as ancestor
> to the autophyletic one; very clearly an ancestor. Seeing the future to
> imagine the former into a sister group relationship is typical of
> phylogenetic insistence on a classification based only on sister groups.
> Evolutionary classification is messy because evolution is messy.
> Simplification of classification by eliminating macroevolution affects
> not just classification, but the perceived reality of natural entities.
> If they are not recognized using words, how does one talk about them?
> *****************************
> Richard H. Zander
> Voice: 314-577-0276
> Missouri Botanical Garden
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> and http://www.mobot.org/plantscience/bfna/bfnamenu.htm
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> *****************************
> -----Original Message-----
> From: taxacom-bounces at mailman.nhm.ku.edu
> [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Boggan, John
> Sent: Friday, July 31, 2009 11:08 AM
> To: taxacom at mailman.nhm.ku.edu
> Subject: [Taxacom] Phylogenetic Classification?
> Maybe this has already come up but I don't have the time or patience to
> wade through all the discussion in the archives.  How are paraphyletic
> species to be treated in strictly cladistic classifications?  I don't
> know about animals, but in plants paraphyletic species are probably
> quite common, i.e., one or more morphologically distinct and
> reproductively isolated species have been derived from a common and
> widespread ancestral species that still exists.  Recognizing those
> derived species makes the ancestral species paraphyletic, but it is
> still a species (or is it?) in that it consists of interbreeding
> populations that are united by gene flow while reproductively isolated
> from their relatives (including the descendant species).  Should the
> derivative species be synonymized under the ancestral species?  And if
> not, what are the phylogenetic implications of the subsequent history of
> these two taxa, one monophyletic but the other not?
> Most molecular phylogenies will not reveal this problem (or at best only
> hint at it) because they sample only one individual of each species.
> But taking the problem to a reasonable extreme, it's theoretically
> possible for a single founding individual of a species, landing on an
> island, to undergo an evolutionary radiation and give rise to numerous
> new genera and species even while the ancestral species still exists on
> the mainland, remaining more or less unchanged.  In practice, extinction
> of populations and entire species probably saves us from this problem.
> But if it could be shown that the founding individual (and thus all its
> descendants) was more closely related to one population of the ancestral
> species than another, the classification of that group could get awfully
> messy...
> John Boggan
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