Answer:
The observed genetic changes mostly likely resulted from the founder effect.
Step-by-step explanation:
The founder effect is a special case of genetic drift. The new population derives from a small number of founder individuals coming from a bigger ancestral population, that established in a new environment. This subgroup carries with them some genetic information that they share with their original population. Over time, some genes can be lost or they can increase in frequency. This might cause reduced genetic variability and enhance the possibilities of a peculiar allelic composition. The new population can be very different from the original one, not only in their genotypes but also in their phenotypes.
In some cases, the founder effect is part of the process of speciation.