Final answer:
The migration pathway of Pseudodiplorchis americanus inside spadefoot toad involves the infection of lung nematodes, which reduces the viability of metamorph cane toads.
Step-by-step explanation:
The migration pathway of Pseudodiplorchis americanus inside spadefoot toad involves the infection of lung nematodes, such as Rhabdias pseudosphaerocephala, which reduces the viability of metamorph cane toads. The lungworm is transmitted to the spadefoot toad through the original toads brought to Australia from South America. The infection with the lungworm can lead to mortality in metamorph toads and affects the growth rate in both adult and juvenile toads.