How does further hybridization affect fertility? Numeruous scientific sites state that hybrids (like mules) are infertile. On the other hand, ligers are known to mate with both tigers and lions and still have viable offspring. **So my question is: if the hybrid is fertile in the first generation, does further mating with either of the parents' species somehow affect its offsping's fertility?** For example: if liger mates with tiger let the odds to produce viable offsping be 50%. If this offsping further mates with tiger, are odds the same or are they lower / higher?

Some first generation hybrids[f1] are viable and fertile, but when they mate with each other or back to either parental species[P}, the successive generations[f2] are sterile or feeble. this concept is known as hybrid breakdown. This is often seen in hybridized forms of domestic crops. I am aware that some female tiger/lion hybrids are fertile, but I'm unaware of successful breeding of the f2 generations. It could be a case of hybrid breakdown.

Article about hybrid breakdown in rice

Hybrid breakdown in Cichlid Fish