[Taxacom] Usefulness vs. convenience (Protista)

[Stephen Thorpe]

I think that the broad issue here is something like this (whether it be at the 
"level" of kingdom, or whatever):
we could retain paraphyletic groups, like Reptilia for example, for reasons of 
stability/pragmatism/etc., but when systematists discover (or claim to discover) 
that Aves are derived from a specific group within Reptilia, it becomes 
psychologically impossible for the cladist types not to change the 
classification to accommodate the "discovery" - they just can't help themselves. 
They don't value stability/pragmatism very highly. The unfortunate thing though 
is that such phylogenetic "discoveries" tend to be rather inconclusive and some 
other study will arrive at a slightly different conclusion, so when they all try 
to accommodate their discoveries by changing the classification, the inevitable 
result is a certain degree of chaos ...

We could just stick with a paraphyletic Prokaryota, a paraphyletic Protista, and 
monophyletic Animalia, Plantae, and Fungi, though the slime molds could pose a 
problem, as could some macro-algae, though there is nothing wrong with putting 
kelp or whatever into Protista, except the notion that Protista all have to be 
unicellular and microscopic ...

Stephen




________________________________
From: "Tony.Rees at csiro.au" <Tony.Rees at csiro.au>
To: kennethkinman at webtv.net; taxacom at mailman.nhm.ku.edu
Sent: Sun, 19 December, 2010 9:43:51 AM
Subject: Re: [Taxacom] Usefulness vs. convenience (Protista)

Hi Ken,

Well I guess I can see one reason why delineation of a separate kingdom 
Chromista might have some appeal - it then allows one to bring in the brown 
multicellular/macro- algae as Chromists even though they are not really 
protozoa/protists in the "unicellular organism" sense, thereby bringing this 
"kingdom" more onto a level with the other multicellular "kingdoms" i.e. 
animals/metazoa, plants, and fungi.; otherwise where do the brown algae live, 
with the abandonment of a polyphyletic "algae".... still a problem I guess, 
unless they are pushed back into plants, which no longer seems either useful or 
convenient? I have seen phylum Heterokontophyta/ stramenopiles/ ochrophyta etc. 
for these but again, you have to allow this group to include both unicellular 
and multicellular forms somehow, including some of the biggest "plants" (at 
least non-animals) of the sea.

Similarly but possibly a bit less intractable, the Rhodophyta, which are not on 
the green plant line so not viridaeplantae at least, but equally not really 
protists; finding a treatment which fits well with these and the brown algae 
seems tricky when some are in/out of kingdom protista/protozoa, but not plants 
either...

Regards - Tony

________________________________________
From: taxacom-bounces at mailman.nhm.ku.edu [taxacom-bounces at mailman.nhm.ku.edu] On 
Behalf Of Kenneth Kinman [kennethkinman at webtv.net]
Sent: Saturday, 18 December 2010 3:56 PM
To: taxacom at mailman.nhm.ku.edu
Subject: [Taxacom] Usefulness vs. convenience (Protista)

Hi Tony,
      As far as I know, most workers who still use Kingdom Protista are
referring to the traditional broad grouping (with both pigmented and
colourless forms).  Chloroplasts have independently invaded colourless
forms several times, so pigmented vs. colourless forms should not be
used to broadly classify protistan taxa at these highest levels.
      Cavalier-Smith (1998) divides Protista into two separate Kingdoms
(Protozoa and Chromista), both of which contain colourless and pigmented
forms (which is not a problem per se).  However, some workers believe
Chromista is polyphyletic (which would be a huge problem).
      My position has always been that whether Kingdom Chromista is
polyphyletic or not, it was still a bad idea, because it unnecessarily
makes his other Kingdom (Protozoa) even more paraphyletic either way.
If Chromista is holophyletic, it basically adds one more exgroup, but
why split Protista if Protozoa is still paraphyletic (there's no
significant advantage gained),  And more importantly, if Chromista is
actually polyphyletic, it is not only unnatural, but adds even more
exgroups to Protozoa.  It then really makes a huge mess of it.
      Either way, it unnecessarily makes the classification more complex
and less stable.  As much as I respect Cavalier-Smith's work, this was
his one major mistake, and it seems to have cast a bit of a cloud over
much of the wonderful work he has done on the phylogeny of protists (and
prokaryotes as well).  I sincerely hope that he will stop trying to
divide Kingdom Protista into separate Kingdoms, and that his work will
then gain more support.  He certainly is not a strict cladist, so why he
wanted to divide Kingdom Protista into separate Kingdoms still puzzles
me.  Especially since he otherwise has incredible insight into how to
best subdivide the protists.
        --------------Ken Kinman
--------------------------------------------------------------
Tony Rees wrote:
Ken - I tend to agree (for what it's worth) - you wrote:
<snip>
Kingdom Protista (as
part of the Five Kingdom classification) has long served as a convenient
paraphyletic group of all eukaryotes except Metazoa, Metaphyta, and
Fungi. Cavalier-Smith has done a fine job of gradually elucidating the
relationships within Kingdom Protista. Unfortunately, he also divided
this perfectly good taxon into separate Kingdoms that proved to be
either wrong or controversial (which has puzzled me since he does
recognize some paraphyletic taxa). </snip>
Yes - now when someone talks about Protista, do they mean:
- colourless unicellular organisms (without the pigmented ones i.e.
"microalgae" or phytoflagellates etc.) i.e. ~= protozoa
- all unicellular organisms, colourless and pigmented i.e. Protista
sens. lat.,  pre C-S "Chromista" split
- same less the heterokont algae and related colourless forms i.e
Protista less Chromista Mk 1
- same less the heterokont algae and related colourless forms, also
rhizaria and alveolates i.e. Protista less enlarged Chromista (2010
version)...
all very confusing (especially to casual readers) and also unstable
between versions and between different authors/usages...
Regards -Tony

______________________________________


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