From: swf@teradata.com (Stanley Friesen)
Newsgroups: talk.origins
Subject: Re: Eukaryotes w/o mitochondria (was Re: The evolution of sexes)
Date: 31 Jul 92 01:02:13 GMT
Reply-To: swf@tdat.teradata.com (Stanley Friesen)
Organization: NCR Teradata Database Business Unit

In article <1992Jul30.170820.2606@bronze.ucs.indiana.edu> jlogsdon@sunflower.bio.indiana.edu (John Logsdon) writes:
|> 
|> I'm not to surprised about evidence for early origin of cps, since I know
|> they have originated at least 4 distinct times.
|>
|Actually it is still unsettled as to whether plastids (chloroplasts being a 
|particular type) are Monophyletic (a single origin) or Polyphyletic (multiple 
|origins). See Gray, MW Trends in Genetics v5: pp294-299 (1989). 

Unsettled!?  When one (small) group of 'algae' has chloroplasts with
an extra membrane and what amounts to its own nucleus?

What else *could* this be except a seperate origin of chloroplasts in this
group of algae, in this case from another type of eucaryote?

(I believe the group in question is the Cryptomonada, but I get the various
'yellow-brown' algae mixed up, so I could be wrong).

And I really do have a hard time seeing a common origin for the 'yellow'
and the 'green' chloroplasts.
|> 
|> I thought I had heard of someone finding DNA in ciliary basal bodies.
|> Has this been refuted?  (Mind, I never did like Margulis' idea of
|> spirochetes as pre-cilia, but this does not mean that some other,
|> otherwise unknown, group of prokaryotes might not be the source of cilia).
|
|You are correct that it was claimed that basal bodies contained DNA in 
|_Chlamydomonas_ (Cell v59: pp121-132 (1989)).  Unfortunately, there have
|been a number critiques of this paper, two papers which I have at hand:
|
|1) Critique based on the physical (size) limitations of the basal bodies 
|and the fact that Anti-DNA antibodies do not stain the "organelles"
|(Cell v62:615-619(1990)).
| 
|2) Critique based on the apparent copy number of the genetic linkage
|group that was purpored to be the basal body DNA. The copy number is
|the same as other nuclear linkage groups, and is apparently unchanged 
|in mutants which lack basal bodies (J. Cell Biology v113: 339-346 (1991)).
|
|In addition, my feeling, garnered second-hand from a friend in the Chlamy 
|community, is that the original reports are in serious doubt.

Ah!  Those two criticisms do indeed sound serious.

Sigh, it is so hard to keep up in all of the fields I am interested in.
(This also shows the dangers of second hand knowledge - I think I got
the original mention from something other than a journal article).

|> |More on the issue of euks w/o mts: Tom Cavalier-Smith wrote a nice "News and
|> |Views" article a few years back (Nature, 1987, v326:332-333) in which he
|> |recognizes at least FOUR major groups of eukaryotic protists w/o mts. 
|> |Archamoebae (to which _Pelomyxa_ belong),  Metamonada (which includes the 
|> |diplomonad _Giardia_), Microsporidia (includes _Vairimorpha_), and Parabasalia
|> |(ie:_Trichomonas_).
|> 
|> An impressive list.  The diplomonad and the parabasalian surprize me.
|> Or are the diplomonads considered to be derived from parabasalians?
|> Or is it only Giardia amoung the diplomonads that lacks mts?
|
|As you probably know, protist systematics (non-molecular) is pretty messy 
|(At least at the level of relationships between major protist groups);
|much like that of early bacterial systematics (pre-Woese).

Duh, tell me about it - Dr. Bovee didn't even pretend his classifications
were in any way phylogenetic.

My senior honors paper was a numerical analysis of amoeba anatomy that
suggested some revisions of amoeba taxonomy.  (And, for those of you who
are not really familiar with microorganisms - yes, amoebas *do* have
structure).

|Cav.-Smith considers Metamonada, Parabasalia, Microsporidia and Archamoebae 
|to be separate Phyla, all of whose members are amitochondrial (ie:diplomonads,
|in Class Anaxostylea, are ALL amitochondrial). _Trichomonas_ (Parabasalian)
|_Giardia_ (Metamonadan), and _Vairimorpha_ (Microsporidian) branch off quite
|separately on the rRNA tree, also supporting them as separate "Phyla."
|(see ref below).

Well, I would certainly agree that being amitochondrial would put them
outside most of the established phyla.  Whether I would place them in
four distinct phyla would depend on *how* distinct the lineages were.
(I shall have to read the paper).

Of course this does rather throw Zoomastigophora into a cocked hat,
as far as being a meaningful taxon :-)
(Not that it was ever terribly good).

|> This certainly sounds reasonable to me.  If indeed the rRNA and protein
|> sequences support the early branching, I would consider the matter just
|> about settled.
|> 
|
|In fact, in a more careful look at the literature,a member of the Archamoebae,
|_Entamoeba_ has had the rRNA sequenced (Sogin, Curr. Opin. Genet. Devel. 
|v1: pp457-463).  It branches off Above the trypanosomes, so therefore may have
|primitively had mt, and subsequently lost them.

In this case, I would tend to say - very likely.  The Entamoeba/Endamoeba
cluster in my senior paper was quite distinct from the Pelomyxa cluster.
(Of course, back then there were still people trying to put Pelomyxa into
the genus Chaos!)

My general impression, back then, was that the parasitic amoebas in the
Entamoeba/Endamoeba group were fairly closely related, and fairly
*specialized*.  Also, parasites do have a strong tendency towards severe
reduction, so loss of mitochondria would not be that out of line in an
internal parasite.  (For that matter I wouldn't be *totally* surprised
if hook worms lacked mitochondria!)

|It is not clear whether the
|phylum Archamoebae is not monophlyetic, and some other members may branch off
|nearer Giardia and the like, or some other scenario(s). More organisms in
|Archamoebae need to be looked at to address this question (to my knowledge
|_Pelomyxa_ has nott been looked at).

What are the groups currently included within Archamoeba?

You have mentioned Entamoeba, which may just be a reduced parasite,
and of course Pelomyxa.  What else?
-- 
sarima@teradata.com			(formerly tdatirv!sarima)
  or
Stanley.Friesen@ElSegundoCA.ncr.com