Most Dreaded Terror 17 Deer mouse

It is the 29 of March, 2018 We are slowly closing in on the mechanism that links kinship with fertility.  My own data suggest that at least one mechanism must be post-zygotic in nature since my fruit flies followed a population time course that could be generated by a computer program that was purely post-zygotic. 
Now I shall offer a piece of evidence suggesting a pre-zygotic component.
Widespread in North America is a rodent called the deer mouse.  Now males compete.  Professor Don Fawcett showed us, when I was at Harvard Medical school, some pictures of different kinds of sperm.  Most of us think of sperm as all looking about alike and rather simple, which is true enough of human sperm.  But that day the good professor showed us the sperm of a Lydian jird.  The head of this gamete was extremely complex.  I suspect now that this was because these sperm compete with each other.  

A jird, think gerbil, is a gentle creature; they make good pets, and I should not be surprised to learn that they don’t fight much in the wild.  But the sperm compete with each other I presume. 
That happens in other animals, but it is not the invariable rule. 

https://www.google.com/search?hl=en&tbm=isch&source=hp&biw=1072&bih=657&ei=SfimWrbtJ4jysAXsg4HYDA&q=deer+mouse&oq=deer+mouse&gs_l=img.1.0.0l10.3936.8550.0.12618.11.10.0.1.1.0.80.604.9.9.0....0...1ac.1.64.img..1.10.601.0..35i39k1.0.fEKNiQ7cN44#imgrc=sm3aC84UdK3T3M: downloaded March 12, 2018
Sperm also cooperate.  In the deer mouse that can stick to each other and form a sort of flying wedge. 

Pictures from Competition Drives Cooperation Among Closely Related Sperm of Deer Mice, Heidi S. Fisher and Hopi E. Hoekstra, NATURE vol. 463. no. 7282 February 11, 2010 page 801.  
Evidently the formation swims faster.
Sometimes they overdo it.  Here are some sperm that have been stained for tubulin:

(I’m sorry I cannot lay hand on a reference)  I fail to sense a competitive advantage this formation confers. 
But here is the zinger.  The males of closely related sperm are much more likely to form up than of “unrelated” – very distantly related – males.  So sperm, at least in this species, recognize kinship. 
If they match, they get together.  All that is needed, then, is that the egg does the same thing and the mechanism exists for pre-zygotic infertility for gametes not sufficiently related.

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