> it is completely clear that heterosis has little or perhaps nothing at all to do with hybrid vigor no matter how often the claim is repeated.

The term "heterosis" was coined by GH Shull to use in reference to hybrid vigour:

> I suggest that instead of the phrases, ‘stimulus of heterozygosis’, ‘heterozygotic stimulation’, ‘the stimulating effects of hybridity’, ‘stimulation due to differences in uniting gametes’, etc ... the word ‘heterosis’ be adopted. The corresponding adjective ‘heterotic’ may also be useful in such expressions as ‘heterotic effects’. -- G. H. Shull (1914)  Zeitschr. f. induktive Abstammungsund Vererbungslehre XII. 127  

and the OED defines heterosis as

> The tendency of cross-breeding to produce an animal or plant with a greater hardiness and capacity for growth than either of the parents; hybrid vigour. 

There is another term for hybrid crosses that display the opposite effects:

> Outbreeding depression is a reduction in reproductive fitness (reduced ability to mate [pollinate], fertilize, produce offspring, survive, or reproduce) in the first or later generations following attempted crossing of populations. 

Frankham, Richard, et al. "Predicting the probability of outbreeding depression." Conservation Biology 25.3 (2011): 465-475.

In the final analysis, breeding produces many surprises. Some mouse lines have been inbred for 100 years, and are quite healthy; as mentioned in the above citation, there is such a thing as "outbreeding depression" but the authors assert "concerns about OD in recently fragmented
populations are almost certainly excessive."

PLB

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