Hi.
I followed the discussion for a while. Jesse, Steve, and Andrew are partially right: inbreeding exists; ooth size depends on size; inbreeding differs among taxa. So long there is an agreement.
The problem with the effect of good nutrition to the success of breeding is, that all carnivorous animals rely on comparable nutritional traits. There is, of course, bad food. But, one can solve this problem by enhancing food quality by wild-caught food and by nutrients and vitamines.
In Europe mantid breeding has a longer tradition. And there are in fact problems with those species that are rarely kept or for which no other bloodlines are available. But: it is also due to the low populations most persons keep. If you just retain one or two females for breeding, your success will not last but for a few generations. I often read things like this in this and other forums. In order to keep the genetic diversity of your captive population high for years, you need at least (!) 5 adult females and 10 to 15 males which have to be paired as often as possible. Too much effort, you think? Well, who said mantids are easy to keep? For one or two, say three generations - ok. But a real breeder needs only rarely fresh blood. And this is not for inbreeding, but for other reasons.
That is: When talking about inbeeding, most people think of degenerative inbreeding. But this form of inbreeding manifestates itself only after many years. Most bloodlines, though, dissapear earlier. This is because there is another problem which works here: the genetic diversity (diversity of alleles of one particular gene) decreases and thus the attractivity of a sister female to a brother male decreases. There are fewer pairings and the ooths hatch badly. Insects as well as some other animals (and humans) can detect the degree of genetic similarity by the pheromones emmited. And, the success of fertilization decreases with increasing genetic similarity.
Secondly, a low genetic diversity means a high degree of homocygoty (see genetics). Every new blood and thus new genes increase the degree of heterocygoty. For natural populations, a high degree of heterocygoty means a fitter population, which is able to face many naturally ocurring problems. That's why new bloodlines are needed: in order to keep the degree of heterocygoty as high as possible. That's why larger captive populations are much more stable than smaller ones: they retain much more different alleles ("kinds") of a particular gene, which can be variably recombined by every pairing. This is also the reason why you should pair your females (preferably after every ooth laid) with as much males as possible. Quantitatively, one mating is sufficient for fertilizing the eggs. Qualitatively, more than one is better!
Regards,
Christian
