Speciation caught in the act:
The evidence at hand suggests that the infertility caused by insufficient kinship is not a speciation effect. This is not “hybrid infertility,” although there is no doubt that such an effect exists. But that is not to say it has nothing to do with speciation. It is what nature has provided us lest speciation effects doom us just when we would have reason to think we were successful.
Now there is an article (LMZ Ecology splits genomes SCIENCE vol. 336 no. 6089 June 29, 2012 page 1621 reviewing Proc.R.Soc. London. Ser. B 279, 10.1098/rspb.2012.0813 (2012)) that has caught a species of stick insects (Timema cristinae) that exploits two different kinds of tree in the process of breaking up into two species, one for each tree I understand. They did genome studies on 8 populations to see what was producing the change. As they expected, differences were greatest between pairs that were reproductively isolated. I think that means bugs on one kind of tree were different from bugs on the other kind. But there was more to it. Distance made a difference, as did climate variables.
Speciation is of interest of course because it is the ultimate driver of the infertility we have discussed. But it is not the direct cause. The direct cause seems to be a specific set of biochemical processes which acts over a wide range of animals and seems, so far as I can tell on little data, to act the same a lot of the time. Not all the time. Some forms have a different pattern than others. But there is broad similarity.
It is useful for the argument, although not crucial, to be able to say “it takes two thousand generations or so for speciation to take effect” as if it were always the same number. It cannot always be the same number exactly, and it doesn’t even have to be close. But it’s easier to understand if it takes about the same time. Of course generation times vary enormously. I usually see speciation times indicated in years. That does not seem to me to be the right unit.
So finding multiple contributions to the process of speciation does cloud the issue a bit. It seems to me that if there are multiple variables the overall variation is going to be greater than if there is just one. Actually it seems to me that all three factors they found seemed to reduce to reproductive isolation. It would be reproductive isolation alone that would impact the need to keep gene pool sizes small. If something else accelerated the process of speciation, that shouldn’t make any difference to ideal gene pool size.
I generally treat speciation as a black box. “It happens in there, so here are the implications. No I don’t know exactly how it happens.” But people are working on it. Whether this ultimately helps with the understanding of the present issue remains to be seen.
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