Farewell to Species - reticulation

[Hubert Turner]

On Sun, 06 Feb 2000 11:22:53 -0500, Thomas DiBenedetto wrote:
>Hubert Turner wrote:
>[in reference to an example where '3' refers to the base of a Y-shaped
>lineage, and'1', and '2' refer to the arms]
>Indeed, 3 becomes the ancestral lineage of the
>clade (1+2+3), but that does not mean that the name of 3 must remain
>attached to the clade. As you write yourself:
>>The name adheres to a taxon. A taxon
>>represents an ancestor and all of its descendants. All of lineage 1
>>is a descendant of the ancestor of 2 & 3.
>When did a terminal branch(no descendants!) stop being a
>taxon???
>----------------------
>Huh? I dont understand your question at all.
You talk of ancestor as the ancestral species in one case, and as the
ancestral specimen (or maybe the ancestral generation?) in the other:
>There are three taxa. Taxon 3 originated at the base of our example.
>It, being a good monophyletic taxon, includes that ancestor and all
>of its descendants. That means all the things
>that we also call 2 and 1. 2 and 1 are also taxa. Terminal taxa. Call them
>species. That is a nice rank we ususally give to termianl taxa. 3 however is
>a higher taxon.
What rubbish!!!!! 3 is a branch on the network. When it was terminal,
it was a species (by your own convention!) When it split into
branches 1 and 2, it became an internal branch. According to the
phylog. species conc., branch 3 stopped being a species then. But
branch 3 can still be identified (as all specimens in that part of
the genealogical network). And why not assign it its own name? Eg.
species 3. The higher taxon is the monophyletic group consisting of
ancestral taxon 3 (species 3!) and all its descendants
(branches/species 2 and 1). Because Archaeopteryx "solnhoferi" (I'm
just making up a name here, to avoid confusion between a species and
a clade) gave rise to all species we recognise as "Aves" today,
doesn't mean that Aves should be replaced by "clade Archaeopteryx
solnhoferi" or vice versa, that Archaeopteryx solnhoferi should be
renamed "Aves".
>But how can we not do that? The taxon is the ancestor and all its
descendants.
As I said, rubbish!!! In traditional (i.e. nomenclatural) usage,
taxon is any grouping of species, from the least inclusive (1
species)  to the most (phyla). Don't try to redefine the meaning of
"taxon".
>If a fossil species were ever to be identified as actually being
>ancestral to later species, then I would have no problem saying that it WAS
>a species at some time. Now it may just be part of a higher taxon.
No, that particular chunk of the genealogical network still is a
species! In addition it is part of a higher taxon, but so is a
terminal species extant right now (Homo sapiens is part of the taxon
Primates is part of the taxon Mammalia is part of the taxon
Chordata). These are not incompatible designations.



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Dr. Hubert Turner
EEW, Sect. Theoretical Biology & Phylogenetics
PO Box 9516, 2300 RA  Leiden, The Netherlands
Visiting address: Van der Klaauw Laboratory, Kaiserstraat 63, Leiden
Phone: +31-71-5274904    Fax: +31-71-5274900
E-mail: turner at rulsfb.leidenuniv.nl
WWW: http://wwwbio.leidenuniv.nl/~turner/index.html

FROM 18 JANUARY TILL MID-APRIL I WILL BE AT THE NEW YORK
BOTANICAL GARDEN AS VISITING SCHOLAR, DOING MOLECULAR
PHYLOGENETIC RESEARCH ON ANACARDIACEAE. MY REGULAR E-MAIL ADDRESS
WILL REMAIN FUNCTIONAL DURING THAT PERIOD.
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