[Taxacom] Drosophila melanogaster name change?

Richard Zander Richard.Zander at mobot.org
Sat Apr 10 16:19:37 CDT 2010


Regarding the paraphyly of Drosophila, the diagrams at the Web site
certainly show (in the caulistic sense) that Drosophila is a progenitor
(as one or more species diagnosable as Drosophila s.str.) of several
autophyletic genera. Okay, that is what it shows. 

My take on molecular analysis is that it shows (ignoring reticulation
and other problems) genetic continuity and isolation of lineages, but
not speciation events because ancestors may survive speciation events.
They do, they do, as is abundantly demonstrated by the myriad
homoplastic species, genera and families making phylogeneticists so
uncomfortable they split and lump to hide what are commonly actually
multiple molecular lineages of the same taxon in phenetic stasis.

So... If your autophyletic genera are robust in expressed traits
important in evolution, then you have a good new classification, and the
model fruit fly should be renamed with a correct name in Sophophora. One
can of course use the nomenclatural synonym "Drosophila melanogaster" as
a kind of taxonomic DOI.

What does "robust" mean? If the lineages chosen as molecular
autophyletic genera are simply largely random sets of species, then one
can usually find a combination of traits that by coincidence serve as
synapomorphies for a group. This does not diagnose a robust taxon. If
the trait combinations (sure, polythetic is okay) are significantly
better for the recognized genera than any other groups formed by random
combinations of species, then you have a robust genus that avoids the
multiple comparisons problem in statistics. If you want to present your
research as "hard science" then you need to quantify the statistical
analysis and do a Bonferroni calculation, or just a joint probability
will do since this stuff is necessarily Bayesian as a one-time
historical reconstruction.

If this seems complex, of course it is. The problem with classification
nowadays is the extreme simplicity of the evolutionary analyses on which
a phylogenetic classification is based. Problematically, a phylogenetic
classification does not help professional evolutionists do research in
evolution because the simplistic assumptions are built-in and affect the
results of research. 

*****************************
Richard H. Zander 
Voice: 314-577-0276
Missouri Botanical Garden
PO Box 299
St. Louis, MO 63166-0299 USA
richard.zander at mobot.org
Web sites: http://www.mobot.org/plantscience/resbot/
and http://www.mobot.org/plantscience/bfna/bfnamenu.htm
Modern Evolutionary Systematics Web site:
http://www.mobot.org/plantscience/resbot/21EvSy.htm
*****************************

-----Original Message-----
From: Kim van der Linde [mailto:kim at kimvdlinde.com] 
Sent: Friday, April 09, 2010 10:40 PM
To: Richard Zander
Cc: Karl Magnacca; taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Drosophila melanogaster name change?

Would you believe that I am not against paraphyletic clades? Probably
not. But I do not have a problem with it. The reasons I do have a
problem with this case are the following:

1. The genus is not a little paraphyletic, but includes at least 12
(twelve) other genera (See here: 
http://www.kimvdlinde.com/professional/DrosophilaSplit.html)

2. The genus as currently defined is highly heterogeneous.

3. Many clades are morphologically more alike the included genera than
to the other clades within the same genus. This is especially striking
between the subgenus Sophophora and the remainder of the genus.

4. The most recent common ancestor of the genus Drosophila is about 63
million years old. Compare that to the most common ancestor of the
Hawaiian 'drosophila' and Scaptomyza, which is only 30 million years
old. Similarly with other genera within and outside the genus
Drosophila.

The larger age difference and some degree of paraphyly are not an issue,
but only if the resulting clades are homogeneous and the excluded clade
is obviously different. That is not happening in Drosophila. The clades
are often morphologically more similar to the closest included genus,
and the genus by itself is highly heterogeneous, to the point that there
is not a single synapomorphy that holds the genus together.
Kim



-- 
http://www.kimvdlinde.com




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