I've scratched my head for some time about mechanisms of speciation. The notion of "incremental change suddenly one morning producing changes that are incompatible with mating" always struck me as a bit magical. I can accept the notion of incremental adjustments in behavior and stimulus patterns and a separation of mating "practice" because of sensory/preference changes. However, the gametes may still be mutually compatible if a couple research assistants mixed them together.
If we are to define "species" on the basis of an inability to produce children, then we need evolutionary changes in genes that will (1) produce the same changes in both males and females and at the same time, (2) produce a number of boys and girls who can mate with each other without the risks of inbreeding.
I couldn't think of anything until yesterday morning when looking at Maynard Smith's new edition of "Evolutionary Genetics." There it was in the first couple of pages.
Viruses could tinker with gene structure, exerting largely the same effects in males and females at the same time and at the same point on the chromosome, and do so to large numbers at once, and produce a cluster of organisms that can breed with each other but not with the parent stock.
Likely not to happen too often. Thus, saltation? (not a popular idea, I understand)
Isolation, in and of itself, despite all kinds of progressive changes in physical appearances, should not produce mating incompatibilities (at least not according the criterion of eggs and sperm that won't merge into a zygote). There was a news release about 5 months ago to the effect that camels and llamas [?] produce fertile young even though the two "species" separated 12 mya. And how many generations (5000?) of dogs underlie two breeds that can still make puppies together?
Any mechanisms besides viral?
Definitely feeling out of my depth.