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"reticulation" (in metazoans)



Tim,
The only major (symbiogenetic) horizontal transfer that I know about (probably lots of minor ones) that has been formally proposed for metazoans concerns the protist origins of cnidocysts (nematocysts, etc.). See "A symbiogenetic theory for the origins of cnidocysts in Cnidaria" (BioSystems, 29:49-58) by Stanley Shostak, 1993.
Such major events have apparently been rare in metazoan evolution, but hard to know how more numerous minor events could be throwing us off track if we are underestimating the frequency of such horizontal transfers (especially in small-sized, poorly-studied invertebrate groups, as opposed to well-known groups like vertebrates and insects). This could even be a factor in what I call the "lophotrochozoa" problem, but I doubt it (I still think that is more a case of molecular plesiomorphies being mistaken as synapomorphies). The rampant amount of horizontal transfer between various protist groups is just beginning to be understood (secondary and tertiary plastids may be just the tip of the iceberg), so there may be some more surprises with respect to metazoans. If I recall correctly, someone has proposed that Kingdom Metaphyta may have arisen as the result of a major symbiogenetic (horizontal) transfer event, but haven't read anything about that recently (I'm not much of a botanist). Even vertebrate evolution may have been affected by some moderate genetic transfers here and there---I wouldn't be totally surprised if it had.
------Ken
********************************************************
From: "Tim Williams" <twilliams_alpha@hotmail.com>
Reply-To: twilliams_alpha@hotmail.com
To: kinman@hotmail.com, NJPharris@aol.com, dinosaur@usc.edu
Subject: Re: Linguistic "budding and reticulation" ... and Roman emperors
Date: Mon, 04 Jun 2001 17:48:57 -0500



Ken Kinman wrote:

Both linguistic and biological evolution are very complicated, and
cladistic
classification only gets the job half done in either case, because it
basically ignores anagenesis and reticulation.


Back in the murky depths of basal eukaryote evolution, the "entanglement"
and exchange of genes between heterogeneous genomes was integral to the
origin of eukaryotes.  Whether by cell fusion or endosymbiosis, this event
(or series of events) gave us our mitochondria and distinctly chimeric
nuclear genome.

And different bacterial species still exchange genes (and gene clusters) on
a regular basis - much to the detriment of humankind, since many encode for
disease-causing traits.

But does anyone know of any examples of reticulating phenetic characters in
animals (mermaids and sphinxes aside).  Unless there are examples, I can't
see how reticulation would cause problems for the cladistic classification
of metazoans.

With plants you can have alloploidy, which complicates things somewhat.
Animals don't do this.  Though I'd like to see where Mr Spock comes up on a
cladogram.  :-)



Nick Pharris wrote:


> >I remember seeing an icon of a Byzantine Emperor that > >had the legend in Greek (if I can remember how to > >spell it correctly) "Basileus Romanoi" - King of the > >Romans. > > Basileus Romaioi (I think).

If anyone cares, if it really translates as "king of the Romans", I think
this would be Basileus Romion.

No, I checked. In the dialect of the Byzantine ruling elite, "Basileus Romaioi" = "King of the Romans". But "Basileia Romaion" = "Kingdom of the Romans".

From memory, I think the title "Basileus" first came into use under the
emperor Heraclius (reigned 610 - 641 A.D.).


Tim




------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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