Re: [asa] Question on speciation

A grad school class mentioned that significant chromosome
rearrangements, interfering with reproductive success, are known in
mice from different valleys in Italy. I don't know details or the
primary literature on it, but that would more or less fit in with the
idea of a mutation that interferes with reproduction getting
established within a small population.

A chromosome rearrangement generally causes poor fertility in the
offspring generation. The individual with the rearrangement can
produce offspring with a normal individual, but their chromosomes have
trouble sorting out properly in meiosis, making it hard for them to
produce gametes. However, if the "hybrid" offspring mate with each
other or with the mutant parent, there's a chance of making a few
more, who could establish a lineage.

Complete infertility of hybrids is an extreme. In many cases, there
is a degree of fertility for hybrid offspring. There's a whole
gradient in the degree of separation. Also, the nature of courtship
and breeding is a factor. In many birds and frogs, for example, a
male that sings a different song won't attract a normal female, even
if they could be bred if placed in the same cage in a zoo. Ecological
and geographic barriers also play a role.

-- 
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
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