Classical systematics fundamental to molecular phylogenetics

Harvey E. Ballard, Jr. hballard at STUDENTS.WISC.EDU
Thu Oct 17 13:08:23 CDT 1996


An issue that seems not to be addressed thus far is the fundamental need
for all phylogenetic studies at the species level to be based on taxonomic
conclusions from comprehensive and modern classical systematic studies,
including typification studies.  I am embarrassed to say how many neophyte
systematists I have become acquainted with who are progressing in molecular
phylogenetic studies of groups whose taxonomy has never yet been adequately
overhauled.  Adequate taxon sampling and clear understanding of taxon
limits, as well as other issues possibly skewing molecular phylogenetic
inferences such as hybridization, are key to any species-level phylogenetic
study.  The wrong name on a voucher specimen means nothing to a molecular
phylogeneticist who is ignorant of the classical systematic information
surrounding a group under study and will inevitably be incorporated into
the "accepted" phylogeny.  All conclusions based on that phylogeny
regarding that mis-identified taxon will be erroneous.  This problem is
also true in cases of taxa with more than one applied name (synonyms) and
is particularly difficult with poorly understood species (or genera) which
have received different names by lay taxonomists (and consequently their
floras and manuals) in different regions of the taxon's range.  I have this
problem with more than a few Viola species in a single small group of
Mexican violets, in which the same species, V. grahamii, has been called
six different species some of which my typification studies have shown to
be synonyms and some, relating to other morphologically and ecologically
distinct species.  Moreover, I discovered two new species that were also
called different names in different parts of their ranges.  Had I not
conducted classical systematic studies to delimit recognizable entities and
completed typification studies to document what names are synonymous, the
phylogeny I got (because I've used some DNA from herbarium specimens as
well and determined correct names through voucher comparisons) would be no
better and no worse than the source of my erroneous information.  In the
most heinous hypothetical example of negligence in disregarding classical
taxonomic bases for a beginning point, I might have been left with an ITS
phylogeny showing relationships of several different synonyms and
mis-applied names for the same few taxa, perhaps making them para- and
polyphyletic because of the random application of the names to the samples,
and any conclusions I might have based on such a phylogeny would have been
ridiculous.

It may sound unnecessarily snooty or narrow-minded, but I confess that I
question the results and conclusions of ALL molecular phylogenetic analyses
at the species level of groups that harbor any taxonomic problems at all
and that have received no serious classical systematic study and
nomenclatural work to typify names.  I worry most about studies in which
authors express no heavy consultation with classical taxonomic
"authorities" and have not included them in the molecular phylogenetic
studies.  Of course, the same problem holds in theory for morphologically
based phylogenetic studies, but someone patient enough to scrutinize
vouchers for morphological features would hopefully have been examining
more than a single sheet of each taxon and, presumably, would also have
obtained a relatively complete library of classical systematic literature
on the study group as a point of departure for developing a tentative list
of morphological characters to evaluate.

In my view, to summarize, whether phylogeneticists recognize the need or
not, the value and credibility of species-level phylogenetic studies (at
least), particularly of taxonomic groups embodying any "difficulty"
whatsoever, hinge on thoughtful and comprehensive classical systematics
research.  If appropriate studies to help elucidate taxon diversity and
taxonomic limits, and even typification studies to determine correct name
applications, are not done, and no taxonomic "authority" is consulted to
correctly determine samples used in phylogenetic analysis, then the
phylogenetic results will always be suspect.  (For what it's worth, I give
this view as a classical systematist who uses both traditional and
molecular data.)  This is a long-winded elaboration of what Hugh Iltis
would say, in short, "one cannot do good biogeography without having first
good taxonomy", and which I would paraphrase to say "one cannot do credible
phylogeny reconstruction without first doing good classical taxonomy".

Now I step down from my pulpit.  Amen.  (And to think that I DID have my
two cups of coffee this morning.)

Harvey Ballard




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