One-island model of migration

The one-island model of migration states that the migration from the mainland to an adjacent island will have a large impact on the island population's gene pool, whereas the migration from the island to the mainland won't have such an impact on the mainland population gene pool. This happens because the mainland has a much larger population than the island. Therefore, the model consists of the effects of migration to the island's gene pool.

Now let's interpret the scenario presented to us:

We can see that both mainlands have a higher percentage of phenotype D, while the same phenotype presents itself with the lowest percentage in the islands. This is consistent with the one-island model of migration, as the genes responsible for phenotype D suffered the processes of evolution in order to have a better fitness to the new environment, leading to a phenotype change. The process of migration generated diversification of the species gene pool.

We can also interpret the presence of phenotypes A, B, and C at the mainlands. It is possible to propose that no migration from the islands to Ontario happened. And migration from the islands to the Peninsular mainland occurred but, as the one-island model of migration states, it did not have a major influence on the population's gene pool.

Reference:

Carr, D. (n.d.). Island migration model. Retrieved March 05, 2021, from https://www.mun.ca/biology/scarr/Migration_model.htm