Final answer:
Both grafting and artificial crossbreeding methods do not result in reproductive isolation between closely related species, leading to shared limitations. Hybrids are generally less fit than purebred species, resulting in the development of reproductive barriers to prevent further hybridization.
Step-by-step explanation:
A shared limitation to both grafting and artificial crossbreeding methods of producing hybrids is that they do not result in reproductive isolation between closely related species. When two species continue to produce hybrids, they develop reproductive barriers to prevent further hybridization and maintain their separate species status. This is because hybrids are generally less fit than purebred species and the two species diverge until hybridization is no longer possible.