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Re: Rearranging the branches of the Tree of Life...



> > As regards lateral transfer - I eagerly await
> (because
> > I certainly won't do it myself... no feathers) the
> > first dedicated study into how that phenomenon may
> > have decreased from "major" to "nearly
> insignificant"
> > immediately preceding the Cambrian Explosion...
> 
> What makes you think it was so important before
> that?
> 
> > *how exactly* did Ediacaran critters reproduce?
> 
> Good question... 

Eaxctly that makes me think so.

Take a "frond". No reproductive organs. That means
that either they reproduced by asexually (fairly
unlikely by that date) or that somatic cells produced
or turned into generative cells.

Either way, in the absence of a mechanism to prevent
this, any cell receiving lateral gene transfer - not
really infrequent even today, as the intestinal mucosa
could attest, though there, a) cells usually don't
live long at all and b) cells have nothing to do with
the germline, so it does not matter evolutionarily -
the odds of LGT affecting the germline are elevated.

So it is very possible that the germline cells in many
Ediacaran taxa were located right in the outer layer
or not far from that and physically unprotected, fair
game for any virus or cytoparasitic/endosymbiotic
bacterium.

This is something that changes fundamentally in
post-Ediacaran fauna, where the germline cells are
usually deep inside the organism, specialized and
protected.

For example in corals with photosynthetic symbionts,
we have data suggesting that LGT is not too
infrequent, even though it in the first place only
affects somatic cells. In plants, gene transfer from
mitochondria to the nuclear genome - which is a weak
version of LGT - never ceased, there is a recent case
reported in (I think) MolPhlyEvol where it affects
molecular phylogeny.

So we know the phenonemnon is still far from
insignificant even today, under conditions that were
probably less prone to it than then. "Less prone" or
"fundamentally less prone", that is the question that
I would like to see addressed. The question how
exactly the Ediacaran fauna managed to reproduce,
thrive and prosper, which is certainly did, will
eventually be addressed, and it is worthwhile while
one is at it to consider the implications.

Which are, simply put, that the molecular trees up to
and including the basic divergence of metazoans were
more like those in bacteria than those of metazoans.
Meaning that there is no easy way to tell the actual
phylogeny, and that it may be impossible with much of
the methods currently used (one might want to try
SplitsTrees though, which I think is not only able to
deal with LGT but also makes it easily recognized in
many cases)


Regards,

Eike


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