Ain't that the way it goes! I'm taking the liberty of pasting the two applicable lines from the New Mexico State University URL in my last post on the grounds of fair use. It is obviously part of notes for a genetics course:
"Hybrid Vigor or Heterosis: An increase in the performance of hybrids over that of purebreds, most noticeably in traits like fertility and sterility (Crossbreeding definition).
Hybrid Vigor or Heterosis: An increase in the performance of hybrids over that of purebreds from linebred families, most noticeably in traits like fertility and sterility (linebreeding definition)." Sterility is an example of negative heterosis, of course.
For the same result in plants, particularly grains, see this obscure report from the Nepal Agricultural Research Council:
http://www.narc.org.np/publicaton/pdf/news...13%20No%202.pdf :
"The rice variety: ‘Loktantra’ (NR 1487-2-1-2-21-1) was released on 4 May 2006. It is a high yielding variety,recommended for farmers to cultivate...
The variety ‘Loktantra’ has been developed in Nepal from a cross of “MAHASURI” and “IR 4547-6-2-2”
"High yielding" here, refers to fecundity, and almost all strains of maize in the U.S. are hybrids for the same reason.
But you are right, too, "positive heterosis" can produce sturdier offspring. Either a Tigron or a Liger has been produced that is too huge to survive in the wild. I have always found negative heterosis rather interesting, as examples of hybrid failure. I was involved marginally, some decades ago, in the filming of prairie chickens in Illinois. We saw one sad example of a not-so-rare hybrid between this bird and the ruffed grouse. He could neither puff out his chest as well as the prairie chickens nor drum as well as the grouse, and was unlikely to find a mate. Even less fortunate are the white tailed and mule deer hybrids that can neither run nor jump as well as their parents and are often the first to be taken by predators.
It seems that mammals do least well at heterosis and more primitive (sorry, less derived) critters, particularly insects, tend to do much better.
Mostly, though, this is a topic which is interesting for its own sake. Everything fits like a puzzle. F1-only creation of artificially bred hybrids is a reminder that the inability of the F2 to produce fertile offspring is a species criterion. The greater ability of "lower" animals to hybridize naturally reminds us of the costs of a high level of derivation or "specialization."
If you say that you have noticed a more rapid reversion to type when two strains of ffs are mixed rather than just one, I obviously have no reason to disbelieve you. This stuff is far too interesting to be the grounds for acrimony.
[And as he returns gracefully to his seat, the crowd goes wild!!
:lol:
]