[Taxacom] Mapping taxa

[Richard Zander]

See if the following logic is appealing:

Phylogenetic classification methods (holophyly) try to reduce
classifications to only those reflecting sister-group relationships,
eliminating any taxa (by splitting or lumping) that are based solely on
traits that are phylogenetically noninformative (that is, uninformative
of sister-group relationships). 

Phylogeneticists often map expressed traits (e.g. morphology)
parsimoniously on a molecular cladogram. 

What this comes down to is that, when mapping a single trait on a tree
((AB)C)...D, if one of the terminal branches has the same trait as the
next lower in the clade (if A shares trait x with C), then that trait is
mapped to the node shared by A and B (and x is a trait of the ancestor
of A and B). This is a kind of paraphyly of traits, where A and C are a
paraphyletic group, as far as morphological traits are concerned. 

If morphological traits can be mapped on a molecular tree, then so can
taxa. Mapping taxa immediately reveals ancestor-descendant
relationships. A paraphyletic group is a mapped taxon. So is the
dependent autophyletic group.

If evolution is descent with modification, then ancestor-descendant
relationships are a more direct indicator of evolution than sister-group
relationships. 

Therefore, if one has ancestor-descendant information from paraphyly
available, one should use it in classification. 

Classification should reflect evolution, whether ascertained by
sister-group or ancestor-descendant relationships. After all,
ancestor-descendant relationships are immediately inferred from the
sister-group analysis. The same techniques are used as in mapping
morphological traits but classification-by-holophyly gets in the way. 

Contriving classifications from both ancestor-descendant and
sister-group relationships demonstrated on a molecular tree does not mix
two different kinds of information but maximizes evolutionary
information about descent with modification, where modification means
change, or differences between taxa.

In my paper
http://tinyurl.com/6frd9l
I extend the above logic to any kind of nonmonophyly.

If it occurs to Taxacomers that I'm repeating much the same things but
in different ways, well . . . . 


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Richard H. Zander 
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Missouri Botanical Garden
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richard.zander at mobot.org
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