I believe that there HAS been an observed case of Drosophila speciation.
I'm not remembering all the details, but the account was published in
Nature or Science about 10 years ago and I think it was reviewed by S.J.
Gould in a Natural History piece.
The event involved a horizontal gene transfer of a P element (a transposon
or something like it) to the fly mediated by a mite. If I remember
correctly, because of this chromosomal change, the population of flies with
the P element couldn't breed with those without it.
I'm not sure that I have time now to track down the details or the
reference, so if anyone in the group has the details, it would be helpful.
[I did manage to find the following URL to some lecture notes that discuss
this case http://darwin.biology.queensu.ca/courses/bio441/lect07.htm ]
In my opinion this is a highly instructive case especially in light of
somewhat failed attempts (although I agree with those who have pointed out
that 100 years is a very short time) to observe Drosophila speciation even
with a lot of help from the geneticists. Horizontal gene transfer is
thought to be responsible for the origin of the complexity of the modern
eukaryotic cell as well. It's also responsible for antibiotic resistance
in bacteria.
TG
_________________
Terry M. Gray, Ph.D., Computer Support Scientist
Chemistry Department, Colorado State University
Fort Collins, Colorado 80523
grayt@lamar.colostate.edu http://www.chm.colostate.edu/~grayt/
phone: 970-491-7003 fax: 970-491-1801