From: JEFF OTTO
  To: MAURY MARKOWITZ
  Re: species

Maury -

Here is another citation to add to your list of speciation events.  This
regards the speciation of laboratory strains of mice from the wildtype
natural population from which they were originally taken.  The full
citation and abstract follow:

Matsuda Y., Hirobe, T., and Chapman VM. 1991.  Genetic basis of X-Y
chromsome dissociation and male sterility in interspecific hybrids.
Proceedings of the National Academy of Sciences.  88:4850-4

Abstract:

A high frequency of X-Y chromosome dissociation (95%) was found at first
meiotic metaphase (MI) in spermatocytes of interspecific hybrids between
laboratory mice, C57BL/6J (BL/6) and Mus spretus, compared with an X-Y
dissociation frequency of ony 3-5% in parental mice.  The X-Y
dissociation in F1 hybrids occurred before diakinesis rather than as a
precocious spermatogeneic breakdown after MI, resulting in male
sterility.  All F1 males were sterile and approximately half of the
backcross males from fertile F1 females corssed with either BL/6 or M.
spretus males were sterile.  Male sterility was highly correlated with
X-Y dissociation in both backcrosses.  All of the mice with hight X-Y
dissociation were sterile and all of the males with low X-Y dissociation
were fertile or subfertile.  This correlation suggested that genetic
divergence of the X-Y pairing region could contribute to the male
sterile phenotype such that  BL/6 X chromosome would not pair with the
M. spretus Y chromosome.  The segregation of species-type alleles of
amelogenin (Amelb and Amels), a distal X  chromosome locus adjacent to
the X-Y pairing region, was followed in backcross males that were
analyzed for X-Y dissociation and sterility (we have used Amel as the
designation for the mouse amelgoenein locus; the current designation for
this locus is Amg).  A 95% concordance between Amelb with fertility and
Amels with sterility was observed in backcrosses with BL/6, whereas the
converse was observed in the backcross to M. spretus.  These results
imply that X-Y pairing plays an important role in male fertility and
suggest that genetic divergence in X-Y pairingregions between Mus
species can contribute to the reproductive barriers between species and
the process of speciation.