What is an example of a post-zygotic barrier?

Hybrid inviability is a prime example of a post-zygotic barrier because it occurs after fertilization has taken place. In this scenario, hybrid inviability refers to situations where hybrid offspring resulting from the mating of two different species fail to develop properly, often leading to their death either before birth or shortly thereafter. This type of barrier effectively reduces the chances of gene flow between species, as it prevents the hybrids, which are not viable, from reaching reproductive maturity and producing their own offspring.

Post-zygotic barriers, such as hybrid inviability, play a crucial role in speciation by ensuring that even if different species mate and fertilization occurs, the resulting hybrids do not survive or are infertile. This contrasts with pre-zygotic barriers, which prevent mating or fertilization from occurring in the first place.