[Taxacom] splitting up genus Drosophila?

[Kenneth Kinman]

Dear All,
     Until today I hadn't ever paid much attention to the taxonomy of
the fly genus Drosophila.  However, it seems that it is paraphyletic and
proposals have been made to split it up (rather than lumping the
daughter taxa into Drosophila).  Splitting it up means that Drosophila
melanogaster would move into a separate genus, which upset some people,
prompting a proposal to change the type species of Drosophila to D.
melanogaster (which has upset even more people).  What a mess (I call it
a mess, not a crisis, since I think it can be resolved one way or the
other).                     
      My own inclination is not to split up Drosophila at all (which
avoids any need to change the type species).  You could have a
paraphyletic Drosophila giving rise to one or more daughter genera, but
unfortunately I am sure strict cladists wouldn't be happy with that.
Therefore my advice to strict cladists would be to lump the daughter
genera into Drosophila (how many depends on the particular phylogenetic
topology you subscribe to).     
       In any case, I suspect most phylogenies would result in the
transfer of genus Scaptomyza into Drosophila.  Would that upset fewer
people than the turmoil that the proposed splitting of Drosophila has
already produced?  Probably yes.  Those who argue that Drosophila is
already too large and "unwieldy", should also consider that splitting
Drosophila into more genera would not only produce the turmoil mentioned
above, but would make the number of genera in Family Drosphilidae
increasingly unwieldly.  It's frankly a balancing act in a relatively
fast evolving family of organisms.                            
      Beyond balancing numbers of taxa, other considerations would also
be any synapomorphies of such an expanded Drosophila.  But as long as
the phylogenetic topology of these subgenera/genera is disputed, it
seems completely premature to apply to the International Commission to
be changing the type species of Drosophila.  Hopefully that will not
happen.  That's the trouble with strict cladism, the temptation to
translate premature findings into permanent taxonomic changes, and thus
unnecessary instability simply to alleviate someone's knee-jerk aversion
to paraphyly.  In the face of that, a middle course would be eliminated,
and often the choice must be made between oversplitting and overlumping.
In this case, oversplitting seems just too destabilizing.                 
       ---------Ken Kinman