In article <199405171401.HAA09692 at net.bio.net>, DRAND at BROWNVM.BROWN.EDU
("David M. Rand") wrote:
>> Further comments on single gene vs. chromosomal changes in speciation:
>> What seems to be interesting about this issue is that there are different
> lineages where karyotypic changes seem to be common and play a major role
> in isolation, whereas other lineages have all sorts of rearragements with
> little evidence for isolation (see above comments by Steve Schaeffer and Eric
(other stuff deleted)
I guess I still don't see the evidence that the karyotype changes are
the cause of isolation or simply a correlate! Once species are
reproductively isolated it seems likely that karyotype changes will occur
in the independent lineages. Proving these changes are the cause of
isolation is an entirely different problem. The only way of doing this is
to find species that are relatively early in the speciation process and see
if karyotype changes are already prevalent. Even this evidence,
unfortunately is only correlative.
The great promise of single (or few) gene theories of reproductive
isolation was that hey were testable. Species can be transformed with the
candidate gene and the the hypothesis actually tested in a rigorous manner
(i.e., gene from species A in species B rescues AB hybrids). These days in
molecular genetics of Drosophila this is the standard. That is if you
claim to have cloned a new homeotic mutant it better rescue a homeotic
phenotype when transformed into a mutant background. Should we as
evolutionists set our standards any lower??
Tony Long
Center for Population Biology
U. C. Davis
Davis, CA
tdlong at ucdavis.edu
