i think so far there is insufficient data.

i would expect that in a spider x spider breeding, you get 33% normals and 66% spiders and a 25% drop in fertility. thats what you get when you make a 2x2 punnet square, remove one of the squares, and count the rest. the same with pinstripe.

the problem is you need a lot of clutches to be sure that its 66% and 33%, instead of lets say 75% and 25%. and you need a lot of clutches to notice a 25% drop in fertility. and if you assume that the female produces more follicles than eggs, meaning not all follicles turn into eggs anyway, you might not even get a drop in fertility. proving it out is incredibly challenging.

what we know for sure is that when you breed spider to spider, or pinstripe to pinstripe, is that you get a lot of spiders or a lot of pinstripes and you wont get any sick or deformed hatchlings. so there is no real reason to avoid these pairings, if you can live with a potential 25% reduction in fertility. but it might add up and the odds might stack against you if you try a breeding like calico spinner to calico spinner.

if anyone knows more its probarbly OWAL, he is really studying this stuff.