Coy flies:
As if the plethora of intriguing articles about epigenetics were not enough, it now turns out the fruit flies have their own way of limiting gene pool size.  (Love Bugs SCIENCE vol. 330 no. 6005 November 5, 2010 page 745)  if a female fruit fly decides to reject an amorous male all she needs to do is properly position her ovipositor and the male has no chance of success.  Very civilized, I should think.  At all events female receptiveness is crucial.  And the females can be choosey. 

Flies were separated into two populations and the populations fed on two different diets.  After many generations, males from one population were rejected by the females of the other population.  This had been noticed before.  What is new is that when the flies were treated with antibiotics this behavior changed and the females became receptive.  Somehow they were able to sense that the suitors were different, and that difference was their bacterial flora.

If you recall from the log of “Exobiology revisited” it takes hundreds or maybe thousands of generations for DNA changes to accumulate and speciation effects to produce infertility between two populations.  In the animals I know about, infertility strikes within a few generations.  That may – wonder, wonder, wonder – may be due to the fact that the mechanism for sensing difference simply saturates after a few generations.  So species have evolved to the point where extinction supervenes if a population gets large and does not promptly return to viable size.

In other words for practical purposes you do not have to marry cousins every single time.  Probably an entire generation could go without kindred marriage and little harm be done.  But eventually the cousin mating must resume for survival. 

Well there really isn’t anything intrinsically evil about a big gene pool.  It just can’t last forever.  But so far as the DNA sequence goes it can last a long time.  So maybe those females sense bacterial differences and that is enough to limit the gene pool for them.

If that works, then for that species maybe there is no other mechanism.  I rather doubt that.  For something this important, redundancy would seem to be in order.  Anyway, there you have an inheritable variation that reduces the fertility of non-kin and it is neither genetic nor epigenetic.

I may have mentioned before the cartoon in which the detective is speaking to a constable in a room with a dead man and a couple dozen bizarre clues saying, “I doubt we ever get to the bottom of this.”

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