I'm interested to know about some certain aspects involving cross breeding or hybridisation between different species of the same genus, i.e. chimpanzees and gorillas or horses and donkeys or wolves and coyotes or lions and tigers, etc. My question involves the effect known as 'heterosis', firstly I'd like to know if all of the F1 progeny would display the effects of heterosis, (is hybrid vigour the same thing?) and would heterosis result in progeny that were very much larger or even giant size compared to either of their parents?
Secondly I would like to know that if there were three species within a genus and a combination of say species A mated with species B and created a fertile hybrid that displayed effects of heterosis, i.e. much larger sized progeny, (lets call it hybrid A), then say species B mated with species C and also produced a fertile hybrid (hybrid B), which also displayed heterosis effects, (as in a much larger sized progeny) and then if a hybrid A was mated with a hybrid B, would heterosis again be possible in the F1 or even subsequent generations of the hybrid AB progeny and would that then mean that the oversized hybrid AB progeny, (lets call it hybrid C) would then be up to double the size or even larger than the original species A, B or C grandparents and would subsequent cross breeding of hybrid C with any of its parent or grandparent species also result in any effects of heterosis, so that even larger hybrids could then be bred and so on and so on until mega fauna sizes could be produced?
Thank you for your question. I also wish to thank the authors of the websites I used. Please note that chimpanzees and gorillas belong to different genera.
Most of the information below comes from an article by Eugene McCarthy (http://www.macroevolution.net/heterosis.html
) and I hope that it answers your questions. Lotsy noted hybrids of snapdragons (Antirrhinum) had characteristics differing from those of the original parents. When Lotsy crossed Antirrhinum glutinosum and A. majus, individuals in the F₂ generation had flowers like those seen in the related genus Rhinanthus. In the F₄ generation Lotsy stabilized a new, true-breeding type.
The California redwood (Sequoia sempervirens) is thought to be a hybrid of the giant sequoia (Sequoiadendron giganteum) and dawn redwood (Metasequoia glyptostroboides), but is taller than both of them and is a good example of heterosis, as described in your question. Hybrids between the Bactrian camel (Camelus bactrianus) and dromedary (C. dromedarius) are partially fertile and are larger, more tolerant and easier to work with than either parent. Hybrids between the Siberian crane (Grus leucogeranus) and white-naped crane (G. vipio) are bigger than either parent. The hybrid produced by a lion and a tigress (a "liger") is usually larger and stronger than either parent, but the cross between a tiger and lioness (a "tigon") tends to be smaller than either parent. Grant and Grant showed that hybrid Galapagos finches (Geospiza) were better able than their parents to feed on seeds after an El Niño event.
Some sunfish (Lepomis) hybrids are more vigorous and aggressive than their parents. Manwell and colleagues showed that this positive heterosis was at least partly due to the enhanced blood chemistry combining factors from both parents.
If a hybrid derived from a cross between two parents is crossed with a third type of parent, the compound hybrid can have traits that are not intermediate between those of the first two parents.
It seems that heterosis varies with different hybrids. The examples given above only represent a small sample of the hybrids produced from closely related species. By choosing the larger hybrids, it is possible that you could breed even larger hybrids, but the following website seems to indicate this is unlikely. http://www.neanderthalproject.com/?tag=heterosis
says that the hybird stock is often larger than either parent, but this need not confer greater fitness. Ligers grow larger than lions or tigers, probably due to “gene imprinting,” as the growth-regulating signal, usually passed by genes from the female lion, are not present in the mating tigress. The hybrid vigour effect (heterosis) begins to fade immediately after the first generation of offspring. While some gene combination may lead to improved reproductive success and an improved line, subsequent generations of young in the new line show variations in fitness as the new line will be swapping and permuting the new gene set within itself or with itself and either or both of its parent species. This suggests that if you breed hybrid C with its parent or grandparent species, there is less chance of it reaching mega fauna size than in earlier crosses. This could be due to a number of reasons, such as the limbs of the hybrid being unable to support the larger body.
I have been to Neanderthal and Munich, which have examples of 'aurochs' and 'tarpans' produced by choosing animals with similar traits to the original animals. There is also work in South Africa, where zebras are being bred to produce animals resembling the quagga.
I hope this helps
All the best