Where'd everybody go?

Mark Siddall mes at zoo.toronto.edu
Sat Feb 4 10:28:32 EST 1995


Joachim asks for some feedback on protistan phylogeny.
In particular it seems he is particularly curious about ciliates.
A few of the most important findings in the last few years are as follows:

(pardon the lack of references but I'm at home... much can be found in
J. Prot. J. Euk. Microbio., Eur. J. Protistol. etc etc).

Most importantly it seems rather solid now that the ciliates, dinoflagellates
and apicomplexans form a clade - the Alveolata sensu Cavalier-Smith.
I will add to that the Haplosporidia (Siddall and Burreson, in press).
In asmuch as these notions have gained strength from the 18S gene, they are
well supported morphologically too.
The ciliates are apparently monophyletic (so long as you do not consider 
opalinids as ciliates which no one does anymore).  The apicomplexans are
monophyletic too and share a more recent common ancestry with the dinoflagel-
lates than with the ciliates.  Perkinsus does not fall out with the apicom-
plexans!  Instead it falls out with the dinos.  
Again in asmuch as these notions are based largely on the 18S gene there
are other data that support it.  For example, the hohlzylinders of
apicomplexans appear to be a vestigal chloroplast as one would find 
in photsynthetic dinos.  Frank Perkins has identified to me 
personally a number of structures in Perkinsus flagellated stages
that are synapomorphic with the dinos.
The basic relaitonships of the Alveolates are as follows:
Ciliates Haplos Apis Perkinsus Dinos
   |       |      |      |_______|
   |       |      |__________|
   |       |___________|
   |_____________|

Other developments relate to the base of the eukaryotic group.
Much has been made of the diplomonads being the earliest divergin
euakryotes.  I have criticised this notion strongly and argued instead that
it was more parsimonious that the Microsporidans fall off first.  
Leipe has similarly found that the earliest= diplomonad hypothesis is
untenable.  Nonetheless, Peattie's flurry of papers in 1990-1991
has run away on us and two papers in J. Euk. Microbiol. still cite
that work as evidence of diplomonads being the earliest diverging
lineage.  


Within-group comparisons have been interesting as well.  In terms of the 
apicomplexans, Barta showed very convincingly that the piroplasms
are adeleids (i.e., more closely related to the heamogregarines than 
to the haemosporinids)  This too has gone largely ignored by the
traditionalists.  
My own work has corroborated Barta's and added some resolution to the 
fish haemogregarine issue.
Furthermore, the haemohormiids are simply not apicomplexans in spite of
everyone having called them piroplasms for years.

There's a smattering for you.

Mark.

-- 
Mark E. Siddall                "I don't mind a parasite...
mes at vims.edu                    I object to a cut-rate one" 
Virginia Inst. Marine Sci.                     - Rick
Gloucester Point, VA, 23062



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