Phylogenetic evidence

[Robin Leech]

I look at Haeckel's term "Phylogeny" and its meanings as a direction for
philosophical concept and thought, and not as means for controlling or
limiting concepts and thoughts.  There has to be a broad interpretation of
the term 'phylogeny' in order to give each of us room to do analysis under
the term.  If there were no broad interpretation and understanding, but a
series of narrow interpretations and understandings, then your analysis and
my analysis will be very different.   If the definitions are "tight and
narrow", then they will have little general applicability, and what you say
and write will have little meaning in relation to what I say and write.

To me, phylogenetics means the discipline of analysis of posssible
historical events, based on evidences, and that we apply, for our
convenience of communication, systematics to that analysis.

Robin Leech

----- Original Message -----
From: "Tom DiBenedetto" <tdib at OCEANCONSERVANCY.ORG>
To: <TAXACOM at USOBI.ORG>
Sent: Tuesday, July 09, 2002 8:35 AM
Subject: Re: Phylogenetic evidence


> Robert Mesibov wrote:
>
> > Haeckel's term 'phylogeny' is now more than 130 years old and it seems
to
> > gain new shades of meaning each time someone sniffs out history in a
data
> > set for the first time. It has a core meaning, though. A phylogeny is a
> > history of evolutionary events.
>
> I find this definition to be overly broad, and thus taking us in the wrong
direction. This
> definition seems to indicate that phylogenetics is equal to the combined
disciplines of
> systematics and evolutionary biology. Phylogeny has always referred to the
historical
> relationships between species and groups of species (from the Greek -
"tribe"-
> "origin"). Phylogenetics is thus equal to the discipline of historical
systematics - the
> enterprise of erecting classifications of species based strictly on their
historical
> relationships.
>
> > OK, so what kind of evidence could be used to erect a phylogenetic
> > hypothesis, i.e. a guess at a phylogeny? Anything that contains traces
of
> > the history of the evolutionary events in question: fossils,
biogeography,
> > morphological character-states, molecular character-states,
host-parasite
> > relationships, etc etc.
>
> And the upshot is that we do not necessarily look with equal interest at
any data that
> touches on the history of evolutionary events, but rather we focus on data
whose
> manifestations are directly reflective of the history of lineage
diversification - e.g. the
> distribution amongst species of particular heritable character states.
>
> > Biogeographic evidence may be mutable and "blurry" at higher taxonomic
> > levels but it does indeed contain traces of history. Every gene, every
> > organism, every evolutionary event has (or had) an address. It often
isn't
> > easy to use biogeographical evidence but it is REAL evidence
nevertheless.
>
> Once again - it is REAL information, but I am not convinced that it can be
considered
> _evidence_ of relationship. Obviously every species has had an address.
But for an
> address to be evidence of relationship one needs to be able to say that
TWO
> species, with the same address, or with adjacent addresses or with
addresses with
> some definable relationship to each other are, on the basis of that
information,
> related to each other in some definable sense. For example - does having
the same
> address give you reason to propose that two species are sister-groups? Or
does
> having adjacent addresses indicate that? It is not enough to say "well,
sometimes it
> might" - because that doesn't advance our understanding one bit. That
would not
> make addresses evidence of anything.
>
> > I gave 3 off-the-top-of-my-stack-of-reprints examples of using
> > biogeographical evidence in an earlier post. The first one concerned
> > reticulation evolution in a Tasmanian conifer genus. The evidence comes
> > from total-genome DNA fragment analysis and from geographical mapping:
the
> > putative hybrid occurs only where the putative parents are sympatric.
> > Imagine for a moment that the putative hybrid had instead been found in
New
> > Zealand. New hypothesis, maybe?
>
> As to the mechanisms of how the evolutionary event happened, yes - maybe.
But a
> new hypothesis as to the relationships - no, not necessarily. If the
character evidence
> indicated that a newly discovered New Zealand species were actually a
hybrid of two
> Tasman species, would you advocate denying that conclusion simply because
you
> could not immediately envision how the hybrid got to New Zealand?
>
> > Turns out that eucalypt cpDNA haplotype families aren't faithful to
> > morphospecies lineages. Instead, they're endemic to particular AREAS
within
> > Tasmania, regardless of what eucalypt morphospecies happen to be living
> > there and housing them. The authors see this as phylogenetic evidence of
> > massive hybridisation in the past, perhaps when the eucalypt ancestors
were
> > crowded together in Pleistocene glacial refuges. Has Tom got an
> > interpretation (a phylogenetic hypothesis) for these eucalypts that
ignores
> > the geographical evidence?
>
> Without reading the papers, off the top of my head I would wonder why the
> geography is seen as crucial to understanding the character evidence. I am
not
> questioning the conclusion of massive hybridization - or the fact that
this might have
> happened in a particular area. But had it happened differently - had the
hybridization
> not necessarily been geographically restricted - we might well have found
the same
> character evidence and reached the same conclusion. What does the
geography add
> to the understanding of relationships? N.B. I recognize that geography
might well add
> to the details of the evolutionary narrative - but my concern is with the
question of
> what is to be considered valid evidence of relationship - phylogeny.
>
> Tom diBenedetto
>