Suppose that after 22 months, guppies from the transplanted population were returned to the source pool. What would most likely happen to those guppies?

When organisms are born in the wild, they tend to start developing an understanding of their surroundings based on their experiences. If an organism is transplanted to a different environment right after birth, it will develop the instincts to survive in that environment. A sudden change in its environment will result in the organism being out to place, possibly unable to cope with the selection pressures of its new environment. This will likely be the case with these guppies. This issue with transplantation is very real with animals born in captivity, which is why many are put through simulation exercises such as hunting and hearing the calls of predators, so that they may be able to survive in the wild, when transferred.